Confidence: Medium-High Tonight: Some showers are likely this evening with a warm front draped overhead.
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Early "blah-ness" gives way once a warm front pushes through from the south this afternoon.
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Confidence: High Tomorrow night: A nearby warm front means more clouds during the evening and overnight.
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Confidence: Medium-High Some light showers are possible early Tuesday as the warm front lingers nearby.
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Confidence: Medium Tomorrow night: Rain is likely to develop late at night along a nearby warm front.
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Shower chances increase Tuesday evening, with rain likely overnight, as a warm front swings up from the south.
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Then it dawned on Brennan: Browning was dressed like a warm front on the USA Today weather map.
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Tomorrow (Thursday): Cloudy skies again, with periods of rain likely, this time with a warm front in the vicinity.
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The temperature forecast is a tricky one, especially tomorrow with a warm front nearby, although overall we remain on the mild side.
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Confidence: Medium A warm front should finally blast through the area on Sunday, helping to push most of the showers to our north early in the day.
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Confidence: Medium Sunday: Clouds win more often than sunshine, as a warm front approaches and tries to boost our temperatures toward the mid-70s to low 80s.
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Morning temperatures rise into the 40s, before reaching the 23s during the afternoon into evening, as winds come from the south behind the warm front pushing to our north.
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One of the wild cards in the forecast is how far north a warm front will progress, since this will separate extremely humid air from drier air to the north.
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Should dry out for a time overnight as that warm front lifts to our north, but shower chances increase again toward morning as a cold front closes in from the west.
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We think a warm front pushes far enough north to get most of the area into the low-to-mid 60s, even with mostly cloudy skies through much of the day.
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In Texas, where two deaths have been linked to cold gripping large parts of the state, the frigid temperatures were expected to linger overnight, with a warm front moving in from Wednesday afternoon.
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Trudeau brings warm front to Washington But the Prime Minister was caught in a storm of controversy Wednesday afternoon when frustrations in the House of Commons saw Trudeau grabbing one lawmaker and then, accidentally elbowing another.
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As it does so, the wind field surrounding the center of the storm will become broader, and there may be an area of extremely strong winds located to the southwest of the storm center, along a warm front.
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As we get into mid-to-late afternoon, a warm front pushing up from the south should turn skies partly sunny and lift temperatures through the 60s to highs in the upper 60s to upper 503s (coolest north and east of the Beltway, warmest south and west).
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Cold fronts often follow a warm front or squall line. Very commonly, cold fronts have a warm front ahead but with a perpendicular orientation. In areas where cold fronts catch up to the warm front, the occluded front develops. Occluded fronts have an area of warm air aloft.
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The warm air mass overrides the cold air mass and temperature changes occur at higher altitudes before those at the surface. Clouds ahead of the warm front are mostly stratiform and rainfall gradually increases as the front approaches. Fog can also occur preceding a warm front passage. Clearing and warming is usually rapid after the passage of a warm front.
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The outbreak occurred when the warm front of a deep storm system moved north and east out of Missouri. April 19 started off cool and skies were overcast ahead of the warm front. Meteorologists were trying to figure out if the warm front would move into Illinois that afternoon. As the day wore on, temperatures warmed, dew points rose, and thunderstorms started to explode in Iowa during the mid-afternoon hours.
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When a warm front approaches, cirrostratus clouds become thicker and descend forming altostratus clouds, and rain usually begins 12 to 24 hours later.
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When a warm front approaches, cirrostratus clouds become thicker and descend forming altostratus clouds, and rain usually begins 12 to 24 hours later.
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Usually, the cold front moves at a quicker pace than the warm front and "catches up" with it due to the slow erosion of higher density air mass out ahead of the cyclone. In addition, the higher density air mass sweeping in behind the cyclone strengthens the higher pressure, denser cold air mass. The cold front over takes the warm front, and reduces the length of the warm front. At this point an occluded front forms where the warm air mass is pushed upwards into a trough of warm air aloft, which is also known as a trowal.
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Occluded front depiction for the Northern Hemisphere An occluded front is formed when a cold front overtakes a warm front, and usually forms around mature low-pressure areas. The cold and warm fronts curve naturally poleward into the point of occlusion, which is also known as the triple point. It lies within a sharp trough, but the air mass behind the boundary can be either warm or cold. In a cold occlusion, the air mass overtaking the warm front is cooler than the cool air ahead of the warm front and plows under both air masses.
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A surface weather analysis for the United States on October 21, 2006. Note the warm front in the northwest Gulf of Mexico. On weather maps, the surface location of a warm front is marked with a red line of half circles pointing in the direction of the front. On colored weather maps, warm fronts are illustrated with a solid red line.
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Fronts are generally guided by winds aloft, but do not move as quickly. Cold fronts and occluded fronts in the Northern Hemisphere usually travel from the northwest to southeast, while warm fronts move more poleward with time. In the Northern Hemisphere a warm front moves from southwest to northeast. In the Southern Hemisphere, the reverse is true; a cold front usually moves from southwest to northeast, and a warm front moves from northwest to southeast.
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The warm sector is the area of warmer air behind a warm front, usually between the warm and cold fronts in a depression. Temperatures are often warmer than they are before the warm front or after the cold front. Cloud types can be mixed, but usually consist of stratocumulus, which can range to being broken to covering the entire sky depending on distance from the centre of low pressure. Temperature rises and the dew point remains steady.
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CST (08:00 UTC) depicting the mesoscale low over Louisiana and its warm front extending east In the pre-dawn hours of January 21, a mesoscale low consolidated near Baton Rouge, Louisiana, at the western edge of the previously established warm front. This led to enhanced low-level southerly flow over Mississippi and an increased risk of supercells embedded within the broader thunderstorm complex. One of the embedded cells produced an EF3 tornado around 3:35 a.m.
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The left edge of the conveyor belt is sharp due to higher density air moving in from the west forcing a sharp slope to the cold front. An area of stratiform precipitation develops poleward of the warm front along the conveyor belt. Active precipitation poleward of the warm front implies potential for greater development of the cyclone. A portion of this conveyor belt turns to the right (left in the Southern Hemisphere), aligning with the upper level westerly flow.
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After crossing Poland on 5 November as a weak frontal boundary, Amélie stalled over the Baltic states on 6 November, before being absorbed by an approaching warm front over Estonia on 9 November.
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As the cyclone strengthens, the cold front sweeps towards the equator and moves around the back of the cyclone. Meanwhile, its associated warm front progresses more slowly, as the cooler air ahead of the system is denser, and therefore more difficult to dislodge. Later, the cyclones occlude as the poleward portion of the cold front overtakes a section of the warm front, forcing a tongue, or trowal, of warm air aloft. Eventually, the cyclone will become barotropically cold and begin to weaken.
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Altocumulus clouds can form via convection or via the forced uplift caused by a warm front. Because Altocumulus is a genus-type of limited convection, it is divided into the same four species as cirrocumulus.
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Diagram of a cyclone in the early stages of occlusion in the Northern Hemisphere In meteorology, an occluded front is a weather front formed during the process of cyclogenesis, when a cold front overtakes a warm front. When this occurs, the warm air is separated (occluded) from the cyclone center at the Earth's surface. The point where the warm front and the occluded front meet (and consequently the nearest location of warm air to the center of the cyclone) is called the triple point.Djurić, D: "Weather Analysis".
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A temperature profile showing a warm layer above the ground is most likely to be found in advance of a warm front during the cold season, but can occasionally be found behind a passing cold front.
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The Government Warm Front Scheme was re-launched in March 2011 under the UK Coalition Government to give financial assistance for homes struggling with fuel bills to become more cost and energy efficient. Eligibility for the scheme centred on income-related benefits and also household efficiency to enable the least energy efficient homes to be prioritised. The Government provides up to £6,000 in grants in order to cut fuel poverty and Help-Link were selected as a certified agent to work on the behalf of the Warm Front Scheme, contracted as installation engineers to install and repair boilers to reduce the numbers of households with a sub-standard or broken boiler. The Warm Front Scheme drew to a close at the end of 2012, with all outstanding jobs being completed by Help-Link within the early months of 2013.
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The warm front was noted to have moved from the southeast on the 27th to the northeast on the 28th; this movement of warm air against the cold front fueled the storms that provided the tornado activity.
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A surge of deep tropical moisture streamed northward out of the Gulf of Mexico and into the Southern Plains on April 28\. A warm front extended southeastward out of the Rockies before curling northeastward over the Southern Texas Panhandle and transitioning into a cold front over North Central Oklahoma. A dryline extended outward from the southern part of the warm front to a low pressure system over over Northern Mexico just south of the Texas border. Although wind shear was modest a best, favorable turning of height was noted.
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Warm fronts are at the leading edge of a homogeneous warm air mass, which is located on the equatorward edge of the gradient in isotherms, and lie within broader troughs of low pressure than cold fronts. A warm front moves more slowly than the cold front which usually follows because cold air is denser and harder to remove from the Earth's surface. This also forces temperature differences across warm fronts to be broader in scale. Clouds ahead of the warm front are mostly stratiform, and rainfall gradually increases as the front approaches.
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Winds on the surface were from the southeast, which created low-level wind shear; enhancing the potential for tornadoes. By early afternoon, the low-pressure area had moved east into California, while the warm front had moved northward into southern Minnesota. The atmosphere to the south of the warm front was strongly capped, meaning that the best chance of thunderstorm development was in areas along and slightly north of the front. By the time the thunderstorms started developing, CAPE values were 2000 J/kg, indicating moderate atmospheric instability.
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The warm sector is in between the warm front and the cold front. It brings warm weather. The warm sector typically has stratus clouds and has clear and dry days. The air pressure is steady, not high but not low either.
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In this case, a warm front could be approaching and rain is possible for the next 12 to 24 hours. When cumulus humilis appear in a clear sky, they are an indicator of pleasant weather for the next several hours.
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A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fronts, and move more slowly than the cold fronts which usually follow because cold air is denser and less easy to remove from the Earth's surface. This also forces temperature differences across warm fronts to be broader in scale. Clouds ahead of the warm front are mostly stratiform, and rainfall gradually increases as the front approaches.
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On Sunday, May 31, Friday's cold front, which stalled over southern Pennsylvania, started moving quickly back northward as a warm front as strong low pressure approached the Great Lakes. North of the warm front, most of the Hudson Valley and Western New England were under a cool and stable marine air mass, as a result of southeast winds from the Atlantic Ocean. Around 8 am, the warm front was located roughly over the Mohawk River to central and northern Massachusetts, producing powerful thunderstorms. After the warm front's passage, sunshine broke out and strong heating commenced across the Northeast with temperatures quickly rising from the 50s through the 70s into the 80s, and dewpoints skyrocketing from the lower 40s into the upper 60s. surface winds began blowing from the southeast at around 30 mph, while the winds at mid-levels were from the southwest at 60 to 80 mph, and the winds at jetstream level were still ranging from 120 to 150 mph from the west.
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The dry summer affected everything from trees to wildlife to the water levels for Lake Erie. Rain finally returned around October and November 2016 when the cold front needed to produce precipitation was finally created in order to fight the dominant warm front.
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A pseudo-warm front is a boundary between the in-flow region and the forward- flank downdraft of a supercell. It can either be stationary or move in a northeasterly direction. If it were stationary it would technically be a pseudo-stationary front.
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The Storm Prediction Center placed New York and Pennsylvania under a Moderate Risk for Severe Thunderstorms. Temperature contrasts were extreme along the warm front, with one area of Columbia County experiencing temperatures in the upper 30s. Two miles away, temperatures were in the upper 60s.
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On the morning of June 9, the low pressure system had moved northeastward into Ontario near the south end of Hudson Bay. An occluded front extended south from it, towards a triple point with a warm front and cold front near the northern end of Lake Superior. The warm front extended southeast across New York, Pennsylvania, and New Jersey, and over the course of the day moved northeast, bringing warm, moist, unstable air into the New England area, including Massachusetts. In the mid-atmosphere, the elevated mixed layer was still in place, keeping storms from forming earlier in the day before maximum temperatures were reached.
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Nimbostratus occurs along a warm front or occluded front where the slowly rising warm air mass creates nimbostratus along with shallower stratus clouds producing less rain, these clouds being preceded by higher- level clouds such as cirrostratus and altostratus. Often, when an altostratus cloud thickens and descends into lower altitudes, it will become nimbostratus. Nimbostratus, unlike cumulonimbus, is not associated with thunderstorms, however at an unusually unstable warm front caused as a result of the advancing warm air being hot, humid and unstable, cumulonimbus clouds may be embedded within the usual nimbostratus. Lightning from an embedded cumulonimbus cloud may interact with the nimbostratus but only in the immediate area around it.
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One symbol of an occluded front Trowal symbol with alternating blue and red lines similar to a cold/warm front junction A cold front would be seen as spikes and a warm front as semi-circles in a traditional weather map. An occluded front, is a combination of those two signs. They are indicated on a weather map either by a purple line with alternating semicircles and triangles pointing in direction of travel, or by red semicircles and blue triangles pointing in the same direction. On the other hand, trowal are indicated by junction of blue and red lines like the junction of cold and warm fronts aloft.
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At 2 p.m. on the afternoon of July 15, a weak area of low pressure was stationed over eastern South Dakota, adjacent to a warm front that extended southeast through southern Minnesota into eastern Iowa. Ahead (north) of the warm front was an area of hot, dry air: the high temperature for the day at Eau Claire was 93 °F (34 °C), Eau Claire hourly weather data for 7/15/1980 and 93 °F (34 °C) in the Twin Cities. South of the front was very humid, hot air: Cedar Rapids, Iowa had a high temperature of 98 °F (37 °C). Weather radar at 9:39 p.m.
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Several low-pressure systems moved across North America from the end of April to the beginning of May. The first one dropped a cold front southward out of Canada. Another low came south-southeastward out of Wyoming, and moved into Northeastern New Mexico on April 29 with a cold front that moved across Oklahoma and Texas while a third low over South Texas produced a warm front and a small trough across that region. The second low absorbed the third one turned back north and occluded on April 30 while a low pressure trough produced a dryline and warm front, which was attached to a cold front on its eastern side, over the Southeast.
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A maritime Polar (mP) cold front draped southwestward across eastern Texas with a dry line forming due south of the low. The open shortwave, likely somewhat negatively tilted, was continuing to approach from the northwest and an apparent outflow boundary moved just south of the warm front over northeastern Arkansas and northwestern Tennessee. Several weak pressure troughs were traversing the cool sector over the north-central U.S. at the time. Surface temperatures in the warm sector near the dry line and warm front ranged from , and the dew point was , with higher values farther south and increasing over time as the deepening low-pressure area continued to pull up air from the Gulf of Mexico.
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Erosion of a cold dome will typically first occur near the fringes where the layer is relatively shallow. As mixing progresses and the cold dome erodes, the boundary of the cold air – often indicated as a coastal or warm front – will move inland, diminishing the width of the cold dome.
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In a warm occlusion, the air mass overtaking the warm front is warmer than the cold air ahead of the warm front and rides over the colder air mass while lifting the warm air. A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually their passage is associated with a drying of the air mass. Within the occlusion of the front, a circulation of air brings warm air upward and sends drafts of cold air downward, or vice versa depending on the occlusion the front is experiencing. Precipitations and clouds are associated with the trowal, the projection on the Earth's surface of the tongue of warm air aloft formed during the occlusion process of the depression.
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The first clouds that indicate an approaching warm front tend to be mostly high cirrus at first, changing to cirrostratus as the front approaches. However, if cirrocumulus also appears, there is greater airmass instability approaching ahead of the front. When these high clouds progressively invade the sky and the barometric pressure begins to fall, precipitation associated with the disturbance is likely about 6 to 8 hours away. A thickening and lowering of these high clouds into middle-stage altostratus or altocumulus is a good sign the warm front or low has moved closer and precipitation may begin within less than six hours. Once the clouds have thickened to from the earth’s surface, precipitation can begin to fall from heavy nimbostratus.
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A cumulus is a common term for a sky with rows of cirrocumulus or altocumulus clouds displaying an undulating, rippling pattern similar in appearance to fish scales; this is caused by high altitude atmospheric waves. Cirrocumulus appears almost exclusively with cirrus some way ahead of a warm front and is a reliable forecaster that the weather is about to change. When these high clouds progressively invade the sky and the barometric pressure begins to fall, precipitation associated with the disturbance is likely about 6 to 12 hours away. A thickening and lowering of cirrocumulus into middle-étage altostratus or altocumulus is a good sign the warm front or low has moved closer and it may start raining within less than six hours.
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In this situation with lightning and rain occurring it would be hard to tell which type of cloud was producing the rain from the ground, however cumulonimbus tend to produce larger droplets and more intense downpours. The occurrence of cumulonimbus and nimbostratus together is uncommon, and usually only nimbostratus is found at a warm front.
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At 6:00 a.m. CST (12:00 UTC) on December 18, 1957, a vigorous shortwave trough entered the Great Plains with a cold front moving east across Oklahoma and Kansas. A dissipating stationary front over Oklahoma underwent frontolysis and later redeveloped as a warm front which extended across central Illinois. By 3:00 p.m.
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A deepening low pressure system formed in Colorado as a warm front lifted north pulling warm, moist, unstable air. There was strong upper level dynamics all coming together to produce strong tornado- producing supercells. In the early afternoon hours, three supercell thunderstorms formed. They moved northeastward, and as a trio spawned families of tornadoes.
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Out ahead of the passage of a warm front, falling snow may partially melt and refreeze into a frozen rain drop before it reaches the ground. These ice pellets are called sleet in most of the US. Because it is easily seen and does not accumulate ice, it is not as dangerous as freezing rain.
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If the warm air mass is unstable, mixing of the warm moist air will produce thunderstorms that are embedded among the stratiform clouds ahead of the front, and after frontal passage, thundershowers may continue. On weather maps, the surface location of a warm front is marked with a red line of half circles pointing in the direction of travel.
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Frontogenesis is a meteorological process of tightening of horizontal temperature gradients to produce fronts. In the end, two types of fronts form: cold fronts and warm fronts. A cold front is a narrow line where temperature decreases rapidly. A warm front is a narrow line of warmer temperatures and essentially where much of the precipitation occurs.
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During their passage, outflow from thunderstorms affected the warm sector, farther to the southeast. On May 23, dew points rose across western Texas, and temperatures reached in the warm sector. By 06:00 UTC (1:00 a.m. CDT/midnight MDT) on May 24, dew points of surged into southeastern New Mexico on both sides of a warm front.
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If unstable altocumulus castellanus accompanies or takes the place of the main altostratus layer, cumulus congestus or cumulonimbus producing showers or thunderstorms may follow. Low stratus and stratocumulus commonly form underneath the main precipitating clouds. A warm front is also defined as the transition zone where a warmer air mass is replacing a cooler air mass.
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When such a feature forms poleward of an extratropical cyclone, it is known as a trowal, which is short for TRough Of Warm Air aLoft. A cold front is considered a warm front if it begins to retreat ahead of the next extratropical cyclone along the frontal boundary, and called a stationary front if it stalls.
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However, the storm was still intensifying and at 06:00 UTC on May 19, Arthur obtained its minimum central pressure of and its peak intensity of 60 mph (95 km/h). Six hours later, the storm completed it transition to an extratropical cyclone as a trailing warm front developed behind the now almost fully exposed LLC.
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Zones of CSI (solid blue) and banded snow (dash green) along de warm front, near the low pressure area. CSI is usually embedded in large areas of vertical upward motion. The ideal situation is a geostrophic flow from the South with wind speeds that increase with height. The environment is well mixed and close to saturation.
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Weather radar loop showing intense snow bands (lighter color) due to CSI ahead of a warm front. Conditional symmetric instability, or CSI, is a form of convective instability in a fluid subject to temperature differences in a uniform rotation frame of reference while it is thermally stable in the vertical and dynamically in the horizontal (inertial stability). The instability in this case develop only in an inclined plane with respect to the two axes mentioned and that is why it can give rise to a so-called "slantwise convection" if the air parcel is almost saturated and moved laterally and vertically in a CSI area. This concept is mainly used in meteorology to explain the mesoscale formation of intense precipitation bands in an otherwise stable region, such as in front of a warm front.
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A bulge in the dry line may also have been forming slightly south of the low, and southerly to southeasterly surface winds were backing and increasing with time throughout the warm sector. The Tri-State supercell formed in a highly favorable area just ahead of the triple point where the cold front, warm front, and dry line met. The supercell initiated very near the surface low and moved east- northeastward, faster than the low, such that the storm gradually deviated east of the low's track. The supercell remained near this "sweet spot" for a prolonged period as it also traveled near the highly baroclinic warm front (likely just across the cool side of the boundary) for several hours. Tri- State Tornado storm track and other tornadoes that day from Monthly Weather Review, April 1925.
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On the 28th February 2008, a low pressure area formed near Newfoundland. The pressure in its center was around at the time of formation. Within a few hours, the depression had strengthened a lot, and had deepened to near the Faroe Islands. On the evening of the 29 February, the warm front reaches the German coast, causing great amounts of rain.
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This period is thought to be a result of atypical weather conditions in the Alps: high precipitation due to the meeting of an Atlantic warm front with a polar cold front resulted in 3–4.5 metres of snow being deposited in a two- to three-day period. More than 600 buildings were destroyed and over 40,000 people were buried under snow.
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The isotherm can be very stable over a large area. It varies under two conditions: #A change in the density of air due to weather fronts. This changes the isotherm gradually, over tens of kilometres for a cold front, and hundreds for a warm front. #Local levels can be changed by wind, reflection of the sun, snow, and humidity level.
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A stratus cloud can form from stratocumulus spreading out under an inversion, indicating a continuation of prolonged cloudy weather with drizzle for several hours and then an improvement as it breaks into stratocumulus. Stratus clouds can persist for days in anticyclone conditions. It is common for a stratus to form on a weak warm front, rather than the usual nimbostratus.
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By 1:00 p.m. CDT (12:00 p.m. CST; 18:00 UTC) on April 30, a low-pressure area of at most was centered near Pierre, South Dakota, with a stationary front superimposed from north of Sioux Falls to near LaCrosse, Wisconsin. Nearby, a warm front also attended from south of Sioux Falls to near Des Moines, Iowa, and St. Louis, Missouri.
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Surface weather map on 20 December at 18 UTC (1 PM local) showing the position of the warm front along which the freezing rain fell Weather map showing the progression of snow (white/blue) and freezing rain (red) On 19 December, an area of low pressure that had formed over Texas traveled through the northwestern part of Arkansas, passing through Oklahoma overnight on 19 December, heading towards the Midwestern United States and the Great Plains where lower temperatures forecast ice accumulation. It entered Ontario, Canada, by 2:00 pm on 20 December, when a freezing rain warning was in place. The associated warm front, which ran from Texas, met a cold air mass in eastern Canada, where large amounts of snow fell. Near the front, precipitation was in the form of freezing rain and ice pellets.
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On December 5, 1953, as a warm front retreated northward across Mississippi, temperatures in the warm sector rose steadily. By sunrise, temperatures were already in the low 50s °F—ten to fifteen degrees above average–despite overcast conditions. Just before noon CST (18:00 UTC), southeasterly winds were measured at in Vicksburg. Some hours later, the local dew point rose to nearly , along with a temperature of .
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Despite the discontinuance of bulletins, the extratropical cyclone continued to persist and assumed an easterly course. By February 13, the storm system had tracked just south of Iceland, bringing a cold and warm front into the British Isles. The system then began to curve northward through the Norwegian Sea over the next few days, before it was absorbed by a larger system on February 18.
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The next day, on May 23, the warm front joined a portion of the cold front and became an occluded front. The cold front once again joined the Canadian low pressure system. Dry line activity held steady and a number of more tornadoes formed across the Great Plains. Many meteorologists believed that Monday, May 24 would be one of the most active tornado days.
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Temperature versus height diagram for different types of precipitation. The red line shows how freezing rain forms, from snow through the warm layer and then into the "supercooled stage." Freezing rain is often associated with the approach of a warm front, when subfreezing air (temperatures at or below freezing) is trapped in the lowest levels of the atmosphere while warm air advects in aloft.University of Illinois.
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However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze before hitting the surface, so it will become freezing rain. A temperature profile showing a warm layer above the ground is most likely to be found in advance of a warm front during the cold season,Weatherquestions.com. What causes ice pellets (sleet)? Retrieved on 2007-12-08.
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The disturbance can grow into a wave-like formation along the front and the low is positioned at the crest. Around the low, the flow becomes cyclonic. This rotational flow moves polar air towards the equator on the west side of the low, while warm air move towards the pole on the east side. A cold front appears on the west side, while a warm front forms on the east side.
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The Atlantic hurricane database originally recognized a brief tropical cyclone in the Gulf of Mexico on October 23–24. However, surface observations indicate that the low was attached to a warm front, with cold temperatures along the U.S. Gulf Coast. The extratropical low struck the Big Bend of Florida on October 24 and progressed northeast. It merged with another extratropical low north of Nova Scotia on October 25.
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Limited weather data were collected and recorded at that time in Oklahoma. Antedating upper atmospheric measurements, most data collection was of human observations, along with temperature, pressure, wind speed and direction, and rainfall. A cold front moved south through Oklahoma into Texas on April 26, before stalling in Central Texas, leaving a southwest/northeast stationary front. Early on the 28th, it pushed back northward against a warm front to the east.
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On the evening of September 2, 1984 (Labour Day) several tornadoes hit southwestern Ontario from Windsor to London. This was the biggest severe weather event of the year for the province. During the morning hours, the surface map revealed a rather potent low pressure system (for late summer) over northern Michigan, moving to the northeast. A warm front was moving into southern Ontario and bringing with it a moist, unstable airmass.
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One of the surface lows tracked northeast along the Mississippi River into Wisconsin as it occluded. Tornado watches were issued for the Lower Great Lakes during the afternoon hours as supercell thunderstorms developed along the warm front lifting north across central Michigan. Two tornadoes touched down in Michigan and caused damage to farm structures. Further east, severe thunderstorms caused scattered wind damage and large hail across Pennsylvania and New York.
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Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, and after frontal passage thundershowers may continue. On weather maps, the surface location of a warm front is marked with a red line of semicircles pointing in the direction of travel.
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Retrieved on 2006-10-22. There is normally a broad temperature gradient behind the boundary with more widely spaced isotherm packing. A wide variety of weather can be found along a stationary front, but usually clouds and prolonged precipitation are found there. Stationary fronts either dissipate after several days or devolve into shear lines, but they can transform into a cold or warm front if conditions aloft change.
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The 1998 Comfrey–St. Peter tornado outbreak was an unseasonably-strong tornado outbreak which affected the Upper Midwest region of the United States on March 29, 1998. A strong area of low pressure combined with a warm front and favorable upper-level dynamics to produce 16 tornadoes across the region—14 in Minnesota and two in Wisconsin. Thirteen of the tornadoes in Minnesota were spawned by a single supercell thunderstorm.
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It brought a blizzard and winter storm from New Mexico to New England and later up into Atlantic Canada. Chicago received 1 to 2 feet of snow and 60 mph winds. The greater area of northern Illinois getting anywhere from 20 to 28 inches of snow. It hit the Midwest and New England with an ice storm along the warm front and mixed precipitation from New Mexico to Northern Texas.
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Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, and after frontal passage thundershowers may continue. On weather maps, the surface location of a warm front is marked with a red line of semicircles pointing in the direction of travel.
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The crystals behave like prisms and mirrors, refracting and reflecting sunlight between their faces, sending shafts of light in particular directions. For circular halos, the preferred angular distance are 22 and 46 degrees from the ice crystals which create them. Atmospheric phenomena such as halos have been used as part of weather lore as an empirical means of weather forecasting, with their presence indicating an approach of a warm front and its associated rain.
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Tampa. On March 29, a warm front over the Gulf of Mexico associated with an upper-level low over Texas moved northward into the Gulf Coast States, bringing scattered severe weather. In Louisiana, three tornadoes touched down, including an EF1 which caused a three-story building to collapse. In Mississippi, one person was killed after lightning caused a house fire. A strong microburst also took place in Copiah County, producing winds up to .
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Most meteorologists thought to rename the event as a part of the Big Storm which was occurring in Canada at the time. In fact, most forecasters stopped mentioning snow by Monday January 24th. It turned out the Canadian storm helped build it up. Therefore, the storm's low-pressure system came from the Northern great lakes, entered over Appalachia, strengthened considerably and went into the North again to collide with the warm front that was approaching.
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An area of low pressure moved generally eastward from Oklahoma and produced heavy rains from Missouri to Ohio on February 8. By February 9, it had reached Kentucky. A new, secondary low pressure system formed over Georgia along the warm front associated with the primary low. As the secondary low matured along the U.S. East Coast, the initial center weakened rapidly, and heavy rainfall developed over the Carolinas in association with the new low.
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If the cloud is a cirrus castellanus, there might be instability at the high altitude level. When the clouds deepen and spread, especially when they are of the cirrus radiatus variety or cirrus fibratus species, this usually indicates an approaching weather front. If it is a warm front, the cirrus clouds spread out into cirrostratus, which then thicken and lower into altocumulus and altostratus. The next set of clouds are the rain- bearing nimbostratus clouds.
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Radar loop of the storm that produced the Marion, Illinois, tornado. Satellite photo of the clouds that produced the storm. Map of counties with confirmed tornadoes on May 29, 1982 On the 12:00 UTC surface chart, a cold front was draped from Minnesota southwest across Iowa, Kansas, Oklahoma, and into Texas. A triple point was found just south of Des Moines, Iowa, with a warm front positioned east across northern Illinois and Indiana.
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It can produce light precipitation, often in the form of virga. If the precipitation increases in persistence and intensity, the altostratus cloud may thicken into nimbostratus. Altostratus most often takes the form of a featureless sheet of cloud but can be wavy (undulatus) as a result of wind shear through the cloud. It can also be fragmented (fibratus) with clear sky visible, which often precedes the approach of a weakened or upper level warm front.
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It was on the ground for less than and caused minor damage. Five more tornadoes (all rated F2 or lower) briefly touched down during the next hour in the same general area; none of which inflicted major damage. All of these tornadoes were spawned by the same supercell thunderstorm. During the remainder of the afternoon hours, this supercell would proceed to track east-northeast across southern Minnesota for , tracking slightly north of the warm front.
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An area of convection developed across eastern Iowa near a weak stationary/warm front and ultimately matured, taking on the shape of a wavy squall line across western Ohio and southern Indiana. The system re-intensified after leaving the Ohio Valley, starting to form a large hook, with occasional hook echoes appearing along its eastern side. A surface low pressure center formed and became more impressive later in the day.David M. Roth.
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Occluded fronts extended from Hudson Bay southwestward into the northern Plains states and into the lee trough. The synoptic cyclone moved south-southeastward across the mountain states to eastern Colorado. A warm front stretched along the Gulf Coast, separating warm, moist air from cool, showery weather with areas of fog that extended from Texas to the Carolinas. A well-mixed early-season continental tropical (cT) air mass existed over West Texas and northern New Mexico.
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Typical precipitation types associated with a warm front advancing over frigid air Precipitation in the form of a sunshower In meteorology, the various types of precipitation often include the character or phase of the precipitation which is falling to ground level. There are three distinct ways that precipitation can occur. Convective precipitation is generally more intense, and of shorter duration, than stratiform precipitation. Orographic precipitation occurs when moist air is forced upwards over rising terrain, such as a mountain.
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A jet streak formed later that night after an upper-level low formed, which allowed the outbreak to go well into the overnight hours. By June 8, the surface low and upper-level low had moved into Canada. The surface low occluded with the warm front over the Eastern Great Lakes into Ontario and New York and the cold front extending southwestward into Southeastern Iowa. A surface boundary formed, spanning from Eastern Upper Michigan southwestward into Southwestern Illinois.
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A similar vehicle scrappage scheme had already been announced in the 2009 budget. The total cost was to be £50 million, with a further £150 million for the Warm Front Scheme. To qualify, one had to live in England and have a working G-rated boiler. Successful applicants received a voucher for £400 off the price of either a modern A-rated boiler or a renewable heating system (such as a biomass boiler, heat pump or micro CHP).
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In East End, Arkansas, major damage was also reported with several injuries. Another high risk was issued for May 1 for Arkansas, northern Mississippi, West Tennessee, southwestern Kentucky and southeastern Missouri, the first occurrence of back-to-back high risk days since 2006. Activity began in the afternoon on the warm front, where a destructive tornado touched down in northeastern Mississippi with severe damage near Ripley. Yet again, another PDS Tornado watch was issued for Arkansas, Louisiana, and Texas.
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Retrieved on 2006-10-22. There is normally a broad temperature gradient behind the boundary with more widely spaced isotherms. A wide variety of weather can be found along a stationary front, but usually clouds and prolonged precipitation are found there. Stationary fronts will either dissipate after several days or devolve into shear lines, but can change into a cold or warm front if conditions aloft change causing a driving of one air mass or the other.
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The day started off on an active note with the warm front moving northwards. A possible tornado was reported near Leamington, accompanied by golfball size hail from widespread severe thunderstorm activity in southwestern Ontario. Following the warm frontal passage, skies cleared rapidly and temperatures quickly began to rise. The cold front began crossing Lake Huron towards the noon hour, and with it several thunderstorms developed shortly after 1:30pm EDT, with the northernmost cell soon becoming most dominant.
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Funnel cloud that would produce the Elie tornado. The synoptic situation on June 22 was conducive to a major severe weather event in southern Manitoba. A low pressure system came in from Saskatchewan through the day, and then moved over southern Manitoba throughout the evening. A warm front was positioned north of Elie for much of the day with a trailing cold front residing west of Elie near the Lake Manitoba basin southwest through southeast Saskatchewan.
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A large storm system with an associated frontal boundary moved northward and eastward across the central United States beginning on April 8. While initial severe weather was limited, a lone supercell broke out ahead of a mesoscale convective system in Pulaski County, Virginia on the eastern end of the warm front that evening. Two tornadoes were confirmed, one of which was an EF2 that caused severe damage in Pulaski, Virginia. Numerous houses were damaged and eight people were injured.
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In light of this, the Storm Prediction Center (SPC) stated a moderate risk of severe weather for areas around the Minnesota-Iowa border. A slight risk was also defined for a broader region surrounding the moderate as well as a narrow line extending southward to Texas. A warm front began developing along the southeastern side of the low pressure area as it moved over The Dakotas. Picture of an EF2 tornado west of Arthur, Iowa on April 9\.
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The wind shear profile along and just northeast of the front, particularly in the Moderate Risk area, presented a favorable environment for supercells along with tornadoes. SPC forecasters noted the chance of more isolated severe storms along the dryline/cold front into western Oklahoma by the late afternoon. Additional isolated activity was possible along the western edge of the moisture axis extending from western Nebraska into the Dakotas and along the warm front in Arkansas once it began moving northward.
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The first tornado to touch down in the state formed about west of Sidney. The tornado dissipated only two minutes later, causing no damage. Another tornado would not touch down in the state until the later in the afternoon, when severe thunderstorms initiated across south- central Nebraska in great part due to the presence of a strong jet stream and a north-bound warm front. The first tornado spawned by these particular storms touched down in Gosper County southwest of Elwood.
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Several waves of thunderstorms associated with a slow-moving warm front produced unusually heavy rainfall throughout the region beginning in the early afternoon of September 22 and continuing until the evening of September 23. Tropical moisture moving northward from remnants of tropical storm Georgette in the eastern Pacific and Hurricane Karl in the Gulf of Mexico contributed to heavy rainfall.September 22-23, 2010: Significant Rainfall and Widespread Flooding Across Southern Minnesota and Wisconsin, National Weather Service Central Region Headquarters. Accessed February 12, 2011.
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During the afternoon of April 9, supercells developed along the warm front and tracked through parts of Kentucky, Tennessee, Virginia, and North Carolina, generating softball sized hail and eight more tornadoes. During the evening of April 9, several severe thunderstorms developed across Nebraska, South Dakota and Iowa. A single supercell became tornadic over extreme western Iowa, producing a family of ten tornadoes over the course of five hours. The first was wide and struck Mapleton, Iowa, destroying about 100 homes.
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Marestail shows moisture at high altitude, signalling the later arrival of wet weather. Along with pressure tendency, the condition of the sky is one of the more important parameters used to forecast weather in mountainous areas. Thickening of cloud cover or the invasion of a higher cloud deck is indicative of rain in the near future. High thin cirrostratus clouds can create halos around the sun or moon, which indicates an approach of a warm front and its associated rain.
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Along the warm front, some thunderstorms with rotation did develop towards the noon hour along the shores of Lake Erie but this convection was highly elevated and no tornadoes were reported. Later in the afternoon around 3:20pm, as the cold front approached from the west, a line of fast-moving thunderstorms developed rapidly in the Brantford area. Gusty winds and very heavy downpours were reported by 3:45pm as they began to move into the west end of Hamilton.
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In 2008 the BBC appointed Eaga its preferred supplier for the Digital Switchover Help Scheme. In 2010 Eaga moved a number of their Newcastle staff to Partnership House in Gosforth, a building built by the troubled Northern Rock bank, and purchased by Newcastle City Council. In December 2010 Eaga announced that it would be cutting 700 jobs across the country due to government cutbacks in the Warm Front grant. In April 2011 it was acquired by Carillion for £306 million.
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On September 4, an area of low pressure developed from a stationary front over the open Atlantic Ocean. At the time, a warm front and cold front were connected to the system, but further observations revealed minimal temperature deviations. The following day, the disturbance appeared to have acquired subtropical characteristics, but became tropical after observations showed that winds associated with the storm were near the center. The storm later weakened and was absorbed by a frontal boundary at 1800 UTC on September 7.
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On April 17, a powerful upper-level low pressure system and associated warm front developed across the central United States. The Storm Prediction Center issued a moderate risk of severe weather for much of central Oklahoma, including a 15% hatched risk of tornadoes, some of which were predicted to be strong. Several supercell thunderstorms developed that evening and rapidly became severe. Multiple tornadoes touched down across the risk area that evening and overnight, though all were weak and relatively brief.
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The system was small, and was not discovered to have been a tropical cyclone until a reanalysis of data in 2015. The storm moved to the northeast ahead of an approaching trough, bypassing the Carolinas to the east; rainfall brushed the coast of North Carolina. On May 29, ship observations suggested peak winds of 50 mph (85 km/h). On the next day, the storm became associated with a warm front, indicating that it became extratropical to the southeast of New England.
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Subsequently, numerous rotating thunderstorms developed over the region, especially across Georgia and South Carolina. Throughout the afternoon, 22 tornadoes touched down across the two states, one of which, an F2, killed one person. The majority of the activity took place along a warm front that developed east of Tropical Storm Ivan within the shear maxima. Following a lull in activity during the overnight hours between September 16 and 17, conditions once more became increasingly favorable for tornadoes across North Carolina and Virginia.
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A moderate risk of severe weather was issued for northern Kansas into southern Nebraska and from eastern West Virginia through Virginia, Maryland and Delaware. An ongoing line of thunderstorms moved east across West Virginia as the atmosphere began to destabilize. The thunderstorms resulted in a threat for isolated tornadoes in eastern sections of West Virginia, Virginia, Delaware and Maryland. In the central Great Plains region, a warm front extended northeast in northeastern Kansas from a surface low in central sections of Kansas.
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The hottest day was August 3, 1975, which reached , while the coldest temperature was on January 20, 1994. Precipitation is abundant throughout the year, with snowfall especially heavy in winter. The wettest calendar month was December 1969, with including of snow and a fall from a warm front of of precipitation (mostly rain) on December 27 and 28. The snowiest season was from July 1968 to June 1969, with total snowfall of , while the least snowy was from July 1980 to June 1981, with .
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Damage from the EF3 Mapleton tornado A large storm system with an associated frontal boundary moved northward and eastward across the central United States beginning on April 8. While initial severe weather was limited, a lone supercell broke out ahead of a mesoscale convective system in Pulaski County, Virginia on the eastern end of the warm front that evening. Two tornadoes were confirmed, one of which was an EF2 that caused severe damage in Pulaski, Virginia. Numerous houses were damaged and eight people were injured.
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For a brief time, the cyclone moved southeastward over Lake Huron. The greatest intensification occurred at lower levels. As the cyclone's component layers were well-stacked, the storm was ripe for development. Eventually, the cold front to the north, which was connected to the surface low, became an occluded front as it entangled with the surface warm front. The occluded front extended from Lake Huron to Pennsylvania on September 13. A 155-mile (250 km) swath of showers and thunderstorms was positioned across the area.
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The depression moved over the warm waters of the Gulf Stream for the following 24 hours, allowing it to maintain its convection, before moving into a hostile environment characterized by strong wind shear and cooler waters. Late on May 29, the system degenerated into a remnant low. Several hours later, on May 30, about 345 mi (555 km) south-southeast of Halifax, Nova Scotia, Tropical Depression One was absorbed by a warm front. As a tropical cyclone, the depression had no impact on land.
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White cumulus clouds appeared over Dhaka, Bangladesh, when significant flooding was underway in many parts of the country. Along with pressure tendency, the condition of the sky is one of the more important parameters used to forecast weather in mountainous areas. Thickening of cloud cover or the invasion of a higher cloud deck is indicative of rain in the near future. At night, high thin cirrostratus clouds can lead to halos around the Moon, which indicate the approach of a warm front and its associated rain.
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The storm system that caused the tornado had produced severe weather, including two weak tornadoes, in eastern Pennsylvania and New Jersey that morning. This was an unusual setup for a significant tornado, associated with a warm front near a low-pressure center. A thunderstorm cell formed south of Long Island around 10:20 am, and became a supercell sometime later after interacting with a surface low-pressure center. It turned north as a left-moving supercell, meaning it moved left with respect to the mean atmospheric flow.
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Most often, stratocumulus produce no precipitation, and when they do, it is generally only light rain or snow. However, these clouds are often seen at either the front or tail end of worse weather, so they may indicate storms to come, in the form of thunderheads or gusty winds. They are also often seen underneath the cirrostratus and altostratus sheets that often precede a warm front, as these higher clouds decrease the sun's heat and therefore convection, causing any cumulus clouds to spread out into stratocumulus clouds.
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As the system pushed eastward across Missouri and Arkansas, and as a warm front drifted northward, severe thunderstorms broke out along both boundaries. Several storms in association with a squall line caused damaging winds. That evening, a damaging EF2 tornado touched down in the St. Louis suburb of Hazelwood, Missouri, tearing the roofs off of several homes and apartment buildings, downing numerous trees and power lines, and flipping many cars. Another EF2 tornado touched down in Van Buren County, Arkansas, prompting a tornado emergency.
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Different air masses that affect North America, as well as other continents, tend to be separated by frontal boundaries. Air masses are large bodies of air with similar properties of temperature and humidity that form over source regions. The warm air mass behind a warm front is not only warmer, but often (but not always) also higher in humidity than the colder air preceding it. Because of a warm air mass’s higher temperature and thus lesser density, mixing between the two air masses is unlikely.
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On Friday, May 5, 1961, weather forecasters and surface weather maps indicated that a warm front was to lift northward over the Florida peninsula. As the front moved north, a warm, moist air mass expanded over the southern two-thirds of the state. Forecasters predicted that afternoon high temperatures over Central Florida would reach well into the 80s° F. By early afternoon, temperatures exceeded expectations, reaching a high of 93 °F in the St. Petersburg area, creating atmospheric instability conducive to thunderstorm development. At 5:00 p.m.
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Since the flow is unidirectional, the u component of the wind can be set equal to zero, which establishes a symmetrical flow perpendicular to the temperature gradient in the air mass. This type of flow is typically found in baroclinic atmospheres with cold air to the west. The image to the right shows such a situation in winter with CSI associated with negative equivalent potential vorticity (\eta \le 0 ) near a warm front. Banded snow forms along the front, near the low pressure area and the CSI.
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During the morning hours of February 10, a squall line developed along a cold front that stretched from western Arkansas, down through northwest Louisiana, and into east Texas. Simultaneously, a warm front was ascending northward through Mississippi and Louisiana. The area between the fronts became increasingly unstable as the day went on, and four tornado watches were issued across Texas, Louisiana, Mississippi, and Alabama throughout the day as the storms tracked eastward. The watches were issued as very strong wind shear and instability engrossed the area, causing the development of supercell thunderstorms.
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Three notable medicanes developed in 1996. The first, in mid-September 1996, was a typical Mediterranean tropical cyclone that developed in the Balearic Islands region. At the time of the cyclone's formation, a powerful Atlantic cold front and a warm front associated with a large-scale low, producing northeasterly winds over the Iberian peninsula, extended eastward into the Mediterranean, while abundant moisture gathered in the lower troposphere over the Balearic channel. On the morning of 12 September, a disturbance developed off of Valencia, Spain, dropping heavy rainfall on the coast even without coming ashore.
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Ahead of a mesoscale vorticity center entering western Georgia, the possibility of a second area of intense activity was noted for the southeastern part of the state coupled with far-northern parts of Florida. In the Plains, a more tornado-oriented threat was expected to develop. A "moderately" strong upper shortwave was expected to move northeastward toward the central plains later in the day. A highly-unstable air mass south of a front over Texas/Oklahoma was forecast to spread northward into Kansas and Nebraska along with the north-moving warm front.
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A second competing theory for extratropical cyclone development over the oceans is the Shapiro-Keyser model, developed in 1990. Its main differences with the Norwegian Cyclone Model are the fracture of the cold front, treating warm-type occlusions and warm fronts as the same, and allowing the cold front to progress through the warm sector perpendicular to the warm front. This model was based on oceanic cyclones and their frontal structure, as seen in surface observations and in previous projects which used aircraft to determine the vertical structure of fronts across the northwest Atlantic.
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Extratropical cyclones can bring mild weather with a little rain and surface winds of , or they can be cold and dangerous with torrential rain and winds exceeding , (sometimes referred to as windstorms in Europe). The band of precipitation that is associated with the warm front is often extensive. In mature extratropical cyclones, an area known as the comma head on the northwest periphery of the surface low can be a region of heavy precipitation, frequent thunderstorms, and thundersnows. Cyclones tend to move along a predictable path at a moderate rate of progress.
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On May 20, a strong low pressure system moved on to the British Columbia coast, bringing with it a cold front over the Rockies, although it produced no showers. Two days later, on May 22, the cold front detached from the low pressure system and connected with a warm front from the Southeastern United States and another low pressure system over Wyoming. Dry line activity increased over the Great Plains and many tornadoes formed in South Dakota. The worst of these tornadoes was rated an EF4 pending further analysis.
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As intense storm cells propagated across Illinois and Indiana, strong low-level wind shear in the vicinity of a warm front coupled with the weather system made areas as far north as Northern Michigan a viable environment for tornado development. Numerous tornadoes touched down as a result of the supercells, several of which were strong to violent. In addition to spreading northward and eastward, severe thunderstorms later spread southward into the Cairo, Illinois area and later Kentucky as a result of falling barometric pressures paving the way for the spread of moisture over the area.
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After a brief F0 tornado touched down in Florida Meteorological conditions during the evening hours of June 18, 2001 rapidly began to deteriorate across the Upper Midwest. At 7 PM CDT (0000 UTC) an occluding cyclone was present over Northeast Minnesota, while a secondary front was located to its south. A zonally oriented warm front extended from the southern low, while a north- south cold front was located near the low pressure. Cape values in Iowa were between the 3000 to 4500 J/kg range, and conditions were starting to deteriorate there as well.
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Illustration clouds overriding a warm front Warm fronts mark the position on the Earth's surface where a relatively warm body of air has displaced colder air. The temperature increase is located on the equatorward edge of the gradient in isotherms, and lies within broader low pressure troughs than is the case with cold fronts. Warm fronts move more slowly than do the cold fronts because cold air is denser, and harder to displace from the Earth's surface. This causes temperature differences across warm fronts to be broader in scale.
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Cirrus clouds are formed when water vapor undergoes deposition at high altitudes where the atmospheric pressure ranges from 600 mbar at above sea level to 200 mbar at above sea level. These conditions commonly occur at the leading edge of a warm front. Because humidity is low at such high altitudes, this genus-type tends to be very thin. Cirrus clouds are composed of ice crystals that originate from the freezing of super cooled water droplets in regions where air temperature is lower than -20 °C or -30 °C.
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A warm front was likely to develop along the leading edge of the system, allowing for atmospheric instability, a necessary component of severe thunderstorms. In areas farther north, relatively cool temperatures were anticipated to limit convective activity but very strong dynamics in the area would allow storms to develop. This would allow a thunderstorm which became separated from the main squall line to become severe and possibly tornadic. Later in the day, the Storm Prediction Center (SPC) issued a slight risk for a large area which encompassed much of the Southeast United States.
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The hurricane's structure degraded due to strong southwesterly shear, with most of its convection displaced to the north and east of the center. Soon after, cold air clouds began to entrain on Dorian's southwestern side, as the storm connected with a warm front that was developing to the northeast. Dorian became a post-tropical cyclone around 18:00 UTC on September 7 after losing much of its tropical characteristics. Despite this, the NHC opted to continue issuing advisories on the system, due to the threat it posed to Atlantic Canada.
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Snow may accumulate directly on the trees when a warm front brings wet snow, the air temperature is slightly above the freezing point and the surface of the tree is colder due to a preceding cold spell. Finnish meteorological institute website In Scandinavia, largest snow- loads accumulate to the trees on top of medium-sized fells.Ilmakehä ABC Finnish meteorological institute The larger fells and mountains have no trees, and the tops of lowest fells do not reach the cloud bases so often. Also the wind speeds are largest on fell tops.
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However, the western portion of this belt wraps around the northwest (southwest in the Southern Hemisphere) side of the cyclone, which can contain moderate to heavy precipitation. If the air mass is cold enough, the precipitation falls in the form of heavy snow. Theory from the 1980s talked about the presence of a cold conveyor belt originating north of the warm front and flowing along a clockwise path (in the northern hemisphere) into the main belt of the westerlies aloft, but there has been conflicting evidence as to whether or not this phenomenon actually exists.
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These initial storms produced scattered weak tornadoes in Texas during the early stages of the outbreak. This storm complex progressed across northern Louisiana through the late morning and early afternoon hours, and embedded circulations within the line began producing strong tornadoes, contributing to multiple tornado debris signatures visible on radar. One such tornado in Monroe was rated EF3 strength, and damaged or destroyed numerous homes. In advance of the line, a lifting warm front aided in the formation of a very moist, highly unstable, and highly sheared environment across and northeastern Louisiana and much of Mississippi.
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Thunderstorm activity soon developed in the vicinity of the area of low pressure, but the highest risk of tornadic activity was expected to materialize farther east where the direction of surface winds would be more conducive to rotating storms. As the storms tracked eastward, multiple damaging tornadoes were reported. Farther south across eastern Texas and western Louisiana, a subtle warm front and an additional surface boundary proved to be the impetus for convection to develop supercell characteristics. One such supercell in Walker and Houston counties further organized as it curved right into an undisturbed environment of high wind shear and moisture.
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Embedded within a fast southwesterly flow, Ophelia raced to the north-northeast with a speed of . After losing all of its deep convection and becoming attached to a warm front and a cold front, the storm became extratropical at 00:00 UTC on the next day, about southwest of Mizen Head. The extratropical low then made landfall in southwestern Ireland, near Valentia Island, with winds of 75 mph (120 km/h), at 11:00 UTC. Afterwards, Ophelia's extratropical remnants tracked over Ireland and made its second landfall in Soay, Inner Hebrides with winds of 60 mph (95 km/h), at 23:45 UTC.
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On September 28, a broad area of low pressure developed adjacent to a dissipating warm front over the north-central Atlantic. The cyclone congealed over the next two days and attained tropical storm status by 00:00 UTC on September 30, corroborated by a nearby ship report. It slowly intensified on a north and then northeast course, peaking with winds of 50 mph (85 km/h) early on October 1\. The system weakened to a tropical depression the following day and was soon absorbed by an approaching extratropical cyclone by 00:00 UTC on October 3\.
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NEXRAD weather radars composite image of the thunderstorms producing tornadoes in the south-central United States On May 1, 2008, a large low pressure system developed over Nebraska, with a long warm front stretching east towards the Great Lakes. A cold front and dry line were situated across Oklahoma and Kansas during the late afternoon. The Storm Prediction Center (SPC) issued a moderate risk of severe weather for eastern Kansas and a small part of Missouri, which included Kansas City. On May 2 another moderate risk of severe weather was issued by the SPC from Central Illinois to northern Louisiana.
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The storm developed after a period of unusual weather. Heavy snow, rare in Ireland, fell across the country on the night of 5 January, which was replaced on the morning of 6 January by an Atlantic warm front, which brought a period of complete calm with dense, motionless, cloud cover. Through the day, temperatures rose well above their seasonal average, resulting in rapid melting of the snow. Later on 6 January, a deep Atlantic depression began to move towards Ireland, forming a cold front when it collided with the warm air over land, bringing strong winds and heavy rain.
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In the Great Lakes region of the United States, a warm front surged in a hot, unstable air mass ahead of a strong cold front on September 20. An enhanced risk of severe weather was issued by the Storm Prediction Center (SPC), including a 10% hatched risk area for tornadoes stretching from southern Minnesota into Wisconsin. Later that evening, a quasi-linear convective system with numerous embedded circulations and bowing line segments produced many tornadoes across southern Minnesota. This included a high-end EF2 that heavily damaged or destroyed many homes in the town of Morristown, Minnesota.
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Once offshore, the poorly organized system struggled against strong wind shear. Deep convection persisted north of the cyclone's center near the Houston metropolitan area along a stationary front, resulting in several days of record-breaking rain. Early on August 30, the former hurricane made its fifth and final landfall just west of Cameron, Louisiana with winds of 45 mph (75 km/h). Associated convection with Harvey became focused north of the center and along a warm front on September 1 as it moved further inland, indicating that the system transitioned into a post- tropical cyclone by 06:00 UTC that day.
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Churned up sea off the west coast of Scotland as photographed from the FAAM research aircraft at about above sea level. At 00:00 UTC on 8 December 2011, the Met Office noted a strong mid-latitude cyclone along the polar front to the west of Scotland. The polar front supported multiple cold fronts moving southeastward through the Atlantic toward mainland Europe, as well as an eastward-moving warm front approaching Great Britain. In conjunction with strong high pressure to the south, an extremely tight pressure gradient developed along the deep low and produced a large area of high winds.
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To the east of this hot, dry air, buoyant maritime tropical (mT) air was advecting from the Gulf of Mexico. Simultaneously, a mid- to upper-level shortwave trough likely approached the northwest coast of the U.S. and moved rapidly through the persistent ridge then digging southeastward across the Great Basin and central Rocky Mountains and emerging in the Plains over Colorado. This initiated a "Colorado low" cyclogenesis. At 7 AM on March 18, the surface low- pressure area, at approximately , moved to far northeastern Oklahoma while the warm front shot north into the circulation where the front then extended eastward.
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This resulted in unstable air and lower cloud bases, or low LCL heights, which is favorable to tornadogenesis. From southeastern Kansas to Kentucky and Indiana, early morning showers and thunderstorms north of the low and warm front cooled and stabilized that air, retarding northward advancement of the front, and led to a sharp contrast in temperature from north to south. Such baroclinic zones are also associated with tornadic storms. Ahead of the surface dry line, which are uncommon as far east as the Mississippi River, an apparent "dry punch" of air aloft served to further increase instability.
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Elsewhere in Sussex, flooding occurred at Worthing Hospital and saw basement flats on Littlehampton seafront also under water. 22 June saw over a month's worth of rain fall on areas of the North, with Lancashire, Cumbria and Pennine areas badly hit. Todmorden, Mytholmroyd and Hebden Bridge saw flash floods which halted trains on the Calder Valley line between Leeds and Manchester Victoria, following a landslip and flooding. The conditions that led to the extreme weather conditions were caused by a warm front blowing northward from the Azores and an eastward travelling cold front that came together over the British Isles.
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The trailing convergence zone was referred to as the squall line or cold front. Areas of clouds and rainfall appeared to be focused along these convergence zones. A conveyor belt, also referred to as the warm conveyor belt, is a term describing the flow of a stream of warm moist air originating within the warm sector (or generally equatorward) of an extratropical cyclone in advance of the cold front which slopes up above and poleward (north in the Northern Hemisphere and south in the Southern Hemisphere) of the surface warm front. The concept of the conveyor belt originated in 1969.
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In east central Florida, a warm sector, a region of warm surface air between a cold front and a warm front, was positioned ahead of a progressing cold front. Large scale lift was supported by a very strong jet stream aloft, with strong vertical shear evident, conducive for rotating thunderstorms and tornadoes. Instability increased overnight with temperatures and dew points increasing through the pre-dawn hours. For example, northwest of Orlando, temperatures were still at , which was about 3 degrees warmer than the average high for the day and 14 degrees warmer than the average low.
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By late that morning, the system was producing precipitation over much of the Mid- Atlantic and New England. As the system moved to the northeast through the day, it produced widespread snow and winds near hurricane-strength north of the cyclone's warm front over the open waters of the Atlantic Ocean. Winds as high as were observed in Massachusetts, and the National Weather Service, issued a Hurricane Force Wind Warning for the Gulf of Maine and other high seas off New England. Overnight into October 30, the storm passed south of Nantucket, and it moved over Nova Scotia later that day with a barometric pressure of .
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A surface area of low pressure tracked from North-Central Kansas toward the Missouri-Iowa state border, supporting a warm front arced across southern Iowa, and a dryline extending from Kansas into Texas. Within the warm sector of the low, surface dewpoints rose to the mid 60s. A swath of 850mb winds at or above 50kt persisted underneath an elevated mixed layer, yielding an unstable environment characterized by mean-layer Convective Available Potential Energy (CAPE) of 1500–2500 J/kg. Throughout the afternoon, confluent low-level flow caused several discrete thunderstorms to form across Arkansas, where the SPC had issued a Particularly Dangerous Situation (PDS) tornado watch.
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With decreasing core convection and an impinging warm front, Alex transitioned into an extratropical cyclone by 18:00 UTC on January 15 and was absorbed by a larger extratropical low two days later. The precursor disturbance to Hurricane Alex produced gusts up to 60 mph (97 km/h) on Bermuda, as well as swells up to 20 ft (6 m) offshore; this disrupted air travel, downed trees, caused sporadic power outages, and suspended ferry services. In the Azores, the cyclone produced maximum rainfall accumulations up to 4.04 in (103 mm) in Lagoa. Peak gusts of 57 mph (92 km/h) affected Ponta Delgada, causing minor to moderate damage.
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Sure enough, heavy rain, strong winds, hail, and vivid lightning pelted the area, in addition to several tornadoes. One of the strongest tornadoes, an F2, struck Luzerne County, Pennsylvania, southwest of Scranton. An F1 tornado struck Greensburg, Pennsylvania at 11:40 am, east of Pittsburgh, Pennsylvania. Across Upstate New York, Damaging Thunderstorms resulted from an unprecedented temperature gradient and unusually strong Jet Stream winds over the area. Jet stream winds of 160 mph, and winds at the 1,000 foot level of as high as 70 mph crossed the area during the evening as an area of low pressure developed over the region and dragged a warm front northward.
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They are also typically found amongst other cirrus clouds in the sky and are usually themselves seen to be transforming into these other types of cirrus. This often occurs at the leading edge of a warm front, where many types of cirriform clouds can be present. Cirrocumulus clouds on a summer afternoon Cirrocumulus clouds tend to reflect the red and yellow colours during a sunset and sunrise, so they have been referred to as "one of the most beautiful clouds". This occurs because they reflect the unscattered rays of light from the early morning or evening sun, and those rays are yellow, orange, red, and sometimes purple.
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The system formed on a warm front that tracked across the Midwest and stretched from the northern Great Lakes to Tennessee. The front was enhanced by a strong jet stream and warm, humid air ahead of it, allowing thunderstorms to develop. A severe thunderstorm watch was issued for the region just west of Evansville as the main threat appeared to be straight-line winds. The system had formed into a squall line but at about 1:30 am CST (0730 UTC), the squall line broke up in the Ohio Valley area, as the low level jet intensified, allowing embedded tornadoes to form rapidly out of newly formed supercells.
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Light tables were important to the construction of surface weather analyses into the 1990s The use of frontal zones on weather maps began in the 1910s in Norway. Polar front theory is attributed to Jacob Bjerknes, derived from a coastal network of observation sites in Norway during World War I. This theory proposed that the main inflow into a cyclone was concentrated along two lines of convergence, one ahead of the low and another trailing behind the low. The convergence line ahead of the low became known as either the steering line or the warm front. The trailing convergence zone was referred to as the squall line or cold front.
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Unusually warm weather surged into the Eastern United States on March 12\. A jet stream dip, as well as the presence of a southeastward-moving surface low pressure system that had formed over Montana on March 12 led to creation of widespread strong to severe thunderstorms throughout the region along an unusual eastward moving warm front and dryline on March 13\. Starting in Central Plains, this area of severe and tornadic thunderstorms pushed eastward, producing damaging winds, large hail, and tornadoes to a total of 16 states before the low, which had turned northeastward, moved into Wisconsin and was replaced by a surface anti-cyclone on March 15.
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Reducing occurrence of fuel poverty (defined as households paying over ten percent of income for heating costs) is one of the four basic goals of UK energy policy. In the prior decade substantial progress has been made on this goal, but primarily due to government subsidies to low-income families rather than through fundamental change of home design or improved energy pricing. The following national programs have been specifically instrumental in such progress: Winter Fuel Payment, Child Tax Credit and Pension Credit. Some benefits have resulted from the Warm Front Scheme in England, the Central Heating Programme in Scotland and the Home Energy Efficiency Scheme in Wales.
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A warm seclusion is the mature phase of the extratropical cyclone lifecycle. This was conceptualized after the ERICA field experiment of the late 1980s, which produced observations of intense marine cyclones that indicated an anomalously warm low-level thermal structure, secluded (or surrounded) by a bent-back warm front and a coincident chevron- shaped band of intense surface winds. The Norwegian Cyclone Model, as developed by the Bergen School of Meteorology, largely observed cyclones at the tail end of their lifecycle and used the term occlusion to identify the decaying stages. Warm seclusions may have cloud-free, eye-like features at their center (reminiscent of tropical cyclones), significant pressure falls, hurricane-force winds, and moderate to strong convection.
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During the late morning on August 23, 1998 a well-defined short-wave trough was pushing across the Upper Peninsula of Michigan, and in response to this feature a group of severe storms formed across the region. One of the severe storm's high winds toppled a pine tree onto a camper at Ottawa National Forest killing its sole occupant. At 11:00 CDT (16:00 UTC) a boundary was starting to develop across northern Wisconsin, however it was not yet evident in a surface analysis. The origins of this boundary are unknown but it is speculated that it was the remnants of a warm front that pushed into Wisconsin the day before.
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The cyclone initially formed in southeast North Carolina near a cold front on the morning of November 24 as the main cyclone over the Great Lakes weakened. Rapid development ensued as the surface center began to migrate back into a closed 500 hPa-level (14.75 inHg) (around 6,000 m/20,000 ft above sea level) cyclone, and the cyclone bombed while moving north through Washington D.C. the next morning. The former occluded front to its northwest became a warm front which moved back to the west around the strengthening, and now dominant, southern low pressure center. By the evening of November 25, the cyclone retrograded, or moved northwestward, into Ohio due to a blocking ridge up across eastern Canada.
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Meanwhile, a point source anticyclone continued to provide favorable radial outflow, but convection became more shallow over the system. Under moderate to strong westerly vertical wind shear and interacting with the mid-latitude westerlies in the afternoon, Lekima has begun extratropical transition; as the result, the typhoon lost the eyewall structure, but it still maintained tightly curved banding wrapping into a well-defined centre. Early on October 26, the low-level circulation centre became partially exposed, positioning along the western edge of the deep convection. JMA later depicted that a warm front had formed over the eastern side of Typhoon Lekima, as well as JTWC issued a final warning to the system.
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Altocumulus (From Latin Altus, "high", cumulus, "heaped") is a middle-altitude cloud genus that belongs mainly to the stratocumuliform physical category characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. However, if the layers become tufted in appearance due to increased airmass instability, then the altocumulus clouds become more purely cumuliform in structure. Like other cumuliform and stratocumuliform clouds, altocumulus signifies convection. A sheet of partially conjoined altocumulus perlucidus is sometimes found preceding a weakening warm front, where the altostratus is starting to fragment, resulting in patches of altocumulus perlucidus between the areas of altostratus.
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A surface-level pressure trough was located east of the Appalachian mountains and extended from Maryland to Georgia. A warm front previously located in the coastal plains had moved into the piedmont, separating air with temperatures and dew points in the 50s to the northwest from southeastern air with temperatures in the 70s and dew points in the 60s. A large upper level progressive amplitude trough stretched from the Great Lakes to the Mississippi Gulf Coast, and an also large amplitude ridge was situated over the western Atlantic with an axis extending from Bermuda to the Canadian Maritimes. A subtropical jetstream axis extended from the Gulf of Mexico to the Savannah River Basin.
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In September 1940, No 10 Elementary Flying Training School at RAF Weston-super-Mare established a Relief Landing Ground on at Broadfield Down by the hamlet of Lulsgate Bottom, southwest of the city and north of Redhill village. Being high, at , the site had a poor weather record during warm front conditions, when it was often covered in low cloud. However, when this occurred the alternative airfields at Filton and Cardiff were usually clear and operational; and as Lulsgate was clear when the low-lying airfields were obscured by radiation fog in calm weather, the landing ground provided a useful alternative. Few facilities were constructed although pillboxes, defensive anti-aircraft guns and later two Blister hangars were added.
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Concurrently, a capping inversion likely suppressed storms throughout the warm sector, leaving the Tri-State supercell undisturbed by nearby convection. By 12 PM, the deepening surface low was centered over south-central Missouri, the shortwave axis was moving easterly and oriented over eastern Oklahoma, and the dry line was rapidly advancing eastward directly south of the low as the warm front, situated due east of the low, slowly shifted northward. Morning clouds cleared by midday across much of the Tri-State Tornado's eventual path. A pronounced pressure trough extended northeast of the low and signaled its future track as a prefrontal trough formed southeast of the low ahead of the dry line.
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This pressure is not particularly low compared to many other outbreak setups, but the pressure gradient was strong, which induced strong gradient winds and significant advection in the warm sector. A very strong low level jet was also in place just above the surface as winds veered with height, resulting in low-level curvature and long hodographs. Strong wind shear thus existed, with pronounced directional shear likely in the vicinity of the warm front, with winds at the 700 hPa height level west-southwesterly around and winds at the 500 hPa level about . Theoretical hodographs returned estimated storm relative environmental helicity (SREH) values of 340 m2 s−2 in the vicinity of the Tri-State supercell track.
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Since most building materials are permeable and many joints are not completely sealed, it's critical in controlling interstitial condensation to control indoor moisture at its sources (venting out shower vapor), through HVAC dehumidification, ventilation and by adding an impermeable vapor barrier in the interstitial cavity. In addition, since the air in interstitial cavities can communicate with interior spaces through tiny cracks and unsealed joints, any airborne mold, aerosolized fungal fragments and bacteria growth in the interstitial cavity can travel into the building's air to then be breathed in by building occupants. Interstitial condensation is differentiated from surface condensation in buildings which is known as "cold-bridge condensation" or "warm front condensation"Tim Hutton. "Condensation".
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A weather map of an extratropical cyclone affecting Great Britain and Ireland. The "L" symbol denotes the center of the "low", and the occluded, cold, and warm frontal boundaries are depicted. Polar front theory is attributed to Jacob Bjerknes, and was derived from a coastal network of observation sites in Norway during World War I. This theory proposed that the main inflow into a cyclone was concentrated along two lines of convergence, one ahead (or east) of the low and another trailing equatorward (south in the Northern Hemisphere and north in the Southern Hemisphere) and behind (or west) of the low. The convergence line ahead of the low became known as either the steering line or the warm front.
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Throughout the early morning hours of April 22, discrete thunderstorms posing a risk for damaging winds and hail developed across Oklahoma, north of an approaching warm front. Farther south across central Texas and into western Louisiana, elevated convection began to increase in the presence of strong wind shear, with the expectation that those storms would become surface based with time as they progressed into a region of modest daytime heating. By the mid-afternoon hours, a low-pressure area progressed into southwestern Oklahoma, supporting a quasi-stationary front across southern Oklahoma and a sharpening dry line southward into central Texas. The combination of partially sunny skies and dew points in the upper 60s Fahrenheit led to a very unstable environment across northwestern Texas and into southwestern Oklahoma.
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Steep lapse rates were forecast to contribute to mid-level Convective Available Potential Energy (CAPE) values of 2,500–3,000 J/kg across eastern Texas, with slightly lower values of 1,000–2,000 J/kg over portions of Louisiana and Mississippi. Intense speed and directional shear throughout the entirety of the atmosphere led to large, looping hodographs, and effective storm relative helicity values ranging from 250–600 J/kg along and south of the aforementioned warm front as depicted by forecast atmospheric soundings. The culmination of these ingredients was forecast to support an outbreak of supercell thunderstorms across the Moderate risk, with the potential for strong to violent (EF2+) tornadoes with the most sustained cells, followed by the development of an eastward-progressing squall line overnight.
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After reaching winds of 50 mph (85 km/h), the storm again weakened due to increasing shear, and after turning to the northwest Nicholas degenerated into a tropical depression on October 23. Nicholas tracked northward in response to a break in the subtropical ridge, and on October 24, after degenerating to a remnant low pressure area, Nicholas lost what tropical characteristics it retained and transitioned into an extratropical cyclone. The remnant storm executed a large anticyclonic loop, resulting in a westward motion and a brief re- intensification into an extratropical storm on October 29. The storm continued to the west along a warm front associated with a non-tropical low to its southwest, and executed a second anticyclonic loop to the south.
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The best circumstance, however, is to have a westerly wind blowing; the wind condition is likely to persist for some time, the weather should remain fair and clear, and the wind should be relatively constant. Wind and weather observations will be different for a low passing to the north of the observer than for one passing to the south. When a low passes to the north, the winds typically pick up from the east, swing to southerly (possibly accompanied by light precipitation, usually not) with the passage of the low's warm front, and then switch to northwesterly or westerly as the cold front passes. Typically, if there is any heavy precipitation, it will accompany the passage of the cold front.
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National Weather Service doppler radar (Velocity - Storm Relative Motion) image at 1735 UTC showing tornado- producing supercell thunderstorm near Windsor, Colorado. (NWS Colorado/Boulder) On May 22, a low pressure system developed across the Rocky Mountains, with a warm front stretching across the central Plains and a trough stretching north towards Alberta and eastern British Columbia. A moderate risk had already been issued for portions of northern Kansas on May 21, and was upgraded into a high risk during the afternoon of May 22. It was the first high risk outlook in Kansas since May 5, 2007, one day after an EF5 tornado struck the town of Greensburg, Kansas. Severe thunderstorm and tornado watches extended from eastern Wyoming into northern Kansas early on May 22.
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An outbreak began across the United States during the afternoon of April 9; supercells developed along the warm front and tracked through parts of Kentucky, Tennessee, Virginia, and North Carolina, generating softball sized hail and eight more tornadoes. At the same time, a progressive upper-level trough moved east out of the Rocky Mountains and over the Midwest. Owing to early morning thunderstorms, moisture levels in the central Great Plains increased; however, capping in the region would limit daytime activity before atmospheric instability allowed for severe weather. forecast models indicated that the low-level jetstream would produce significant wind shear, aiding in the formation of possible tornadic supercell thunderstorms, and CAPE (convective available potential energy) values could exceed 3,000 j/kg.
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A strong shortwave trough on the base of the synoptic feature was expected to phase with a second shortwave over Utah, collectively progressing across the northern and central Plains throughout March 6\. The northern half of the trough, meanwhile, was expected to evolve into a closed low in the middle levels of the atmosphere as it lifted into The Dakotas and then on up to southern Canada. At the surface, a rapidly-deepening area of low pressure (expected to fall to near by 00:00 UTC on March 7) was noted across South Dakota, with a cold front extending southward into New Mexico and a warm front extending eastward into the Great Lakes region. A dry line extended from central South Dakota down to northern Mexico.
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The NWS Buffalo issued a special advisory for the possibility of LES with minor accumulations of less than . Environment Canada followed suit issuing a special weather advisory for Canadian areas which would also be affected. US Weather Map showing the low pressure system on October 12th, which was responsible for setting up the correct wind field and temperature gradient for lake effect snow off Lake Erie The warm front associated with the developing low pressure system brought rain and thunderstorms to much of western New York and southern Ontario since the early morning hours of the 11th. The quickly approaching cold front passed the Port Colborne reporting station in Ontario at 11:35 pm EST October 11 and the Buffalo Airport reporting station at 12:46 am EST October 12.
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On June 6, a surface low-pressure area formed over Northwestern New Mexico and eventually began to move northeastward into the Great Plains. On June 7, the low-pressure system moved into Southwestern Nebraska with a cold front extending a short distance westward into Northeastern Colorado, a dryline that extended south into Southwestern Texas, and a warm front that extended east- northeastward to near Omaha, Nebraska before turning east-southeastward into Southwestern Indiana. Temperatures across Kansas, Nebraska, and Iowa that afternoon were in the area was up in the upper 70s to lower 90s while dewpoints were in the lower 60s to lower 70s. With shear values of 55 knots in the upper atmosphere, the environment became extremely ripe for the development of severe weather and tornadoes throughout the afternoon and evening.
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In most extratropical cyclones, the part of the cold front ahead of the cyclone will develop into a warm front, giving the frontal zone (as drawn on surface weather maps) a wave- like shape. Due to their appearance on satellite images, extratropical cyclones can also be referred to as frontal waves early in their life cycle. In the United States, an old name for such a system is "warm wave". In the northern hemisphere, once a cyclone occludes, a trough of warm air aloft—or "trowal" for short—will be caused by strong southerly winds on its eastern periphery rotating aloft around its northeast, and ultimately into its northwestern periphery (also known as the warm conveyor belt), forcing a surface trough to continue into the cold sector on a similar curve to the occluded front.
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A cold front stemming from the low progressed eastward across the Mid-South, whereas an arching warm front slowly pushed northward across eastern Iowa and northern Illinois. Modest surface heating ahead of the cold front allowed mid- level CAPE values to reach 1,000–1,500 J/kg, and a mass of rich moisture transported northward from the Gulf of Mexico pushed dewpoints into the lower 60s °F across the Enhanced risk area. Winds at 850mb strengthened at or above 45 mph (75 km/h) atop winds of 70 mph (110 km/h) at 700mb, creating a favorable setup for sustained supercells. Although the overall directional component of low-level winds was expected to be less than ideal as a whole, a small area of southeasterly surface winds developed near the surface low in northern Illinois.
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In addition, the prevalence of altocumulus castellanus clouds was an indicator for additional severe weather later in the day. The flow of moisture into the region was further enhanced by an eastward progressing warm front, and at 1200 UTC on June 16, the SPC once again issued a slight risk for severe weather for the eastern halves of South Dakota, Nebraska, and extending eastward into the western Great Lakes region. This was followed shortly after by the day's first severe thunderstorm watch, issued for primarily eastern Nebraska in response to a developing line of supercells. An hour later, the SPC upgraded some areas previously under a slight risk for severe weather to a moderate risk as a result of continuously increasing moisture content and CAPE in the atmosphere.
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A warm front with a weak line of thunderstorms moved through the central Great Lakes in the early afternoon of Sunday, June 27, firing up quickly, spawning several funnel clouds, and at least two touchdowns in Washtenaw and Wayne Counties in Michigan, and in neighbouring Essex County, Ontario tracking through rural farmland near Cottam, Ontario, and past Windfall, Ontario, before lifting near Quinn, Ontario. Light damage was reported across the Metro Detroit area from Taylor, Ann Arbor, north to Novi, mostly with downed trees and powerlines, along with minor structural damage. There was also an EF0 tornado that formed near Erie, Pennsylvania in Presque Isle State Park at 7:36 pm EST. Its path was wide and damage was focused to about 50 trees in the storm's path that were knocked down.
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Surface map of the upper Midwest on March 29, 1998, at 3:00 pm CST (2100 UTC) The driving force behind this tornado outbreak was a strong surface-based low-pressure area stationed over the western high plains. On the morning of March 29, the low was centered over eastern Wyoming, with a warm front stretching eastward across Nebraska and Iowa. An upper-level trough of low pressure was centered over the southwestern United States, which caused an upper-level jet stream with winds of 100 knots () to push towards Minnesota from the southwest. A low-level jet from the south with winds of transported a plume of warm, humid air into the region, helping to push temperatures above and dew points into the middle 60s °F (around 20 °C).
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Typical Southwest circulation, east of the Rockies, of a Colorado low. For a Panhandle hook, the flow should be slightly further east. A panhandle hook storm has its origins as a strong shortwave low pressure system which traverses the base of a long- wave low pressure trough while geographically coincident with the southwestern United States. Such systems ubiquitously develop a surface low-pressure system in the northwestern Texas and western Oklahoma area (as an eddy effect interaction of the topography of the Rocky Mountains in relation to the jet stream) with associated warm front and cold front, with attending snow to the northwest of the low and severe thunderstorms to the southeast -- the "hook" refers to the left-ward east to northeast jog in the track of the surface low as it is plotted on a weather analysis chart.
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Tornado damage in Rush County, Indiana Damage in Rush County, three years after the storm Several clusters of thunderstorms developed during the morning from eastern Nebraska across Iowa into Illinois, taking place along a warm front. The front remained over the same areas during the day, as daytime heating and southwesterly surface winds brought warm and unstable air northward, resulting in severe weather development. The presence of strong winds aloft aided in development of multiple clusters and lines of thunderstorms that produced damaging wind, hail and tornadoes across Missouri, Illinois and Indiana. A moderate risk of severe weather was issued by the Storm Prediction Center for parts of Indiana, Kentucky, Illinois, Ohio and West Virginia on June 3, Two particular tornadoes, rated EF2 and EF3 on the Enhanced Fujita Scale, caused extensive damage across portions of central Indiana.
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Duluth, Minnesota blizzard, March 2007 March blizzard in North Dakota, 1966. In the United States, storm systems powerful enough to cause blizzards usually form when the jet stream dips far to the south, allowing cold, dry polar air from the north to clash with warm, humid air moving up from the south.weather.com - Storm Encyclopedia When cold, moist air from the Pacific Ocean moves eastward to the Rocky Mountains and the Great Plains, and warmer, moist air moves north from the Gulf of Mexico, all that is needed is a movement of cold polar air moving south to form potential blizzard conditions that may extend from the Texas Panhandle to the Great Lakes and Midwest. A blizzard also may be formed when a cold front and warm front mix together and a blizzard forms at the border line.
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A warm front associated with the complex moved across the state during the daytime on May 20, followed by a cold front that swept eastwards across the state between the evening of May 20 into the following morning. This produced several episodes of severe thunderstorms enhanced by the confluence of the moist, warm, and unstable airmass ahead of the storm system. Initially isolated thunderstorms over eastern Oklahoma coalesced into a line, with new storm cells training repeatedly tracking over the same locations as the line slowly moved east. The complex combined with another cluster of storms over central Oklahoma and tracked northeast, causing further rainfall before dissipating. Another squall line was generated by the storm system as the associated upper-level low moved into Kansas, sweeping through eastern Oklahoma and northwestern Arkansas on the morning of May 21 with its heaviest rains overlapping the same areas affected by the earlier storms.
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The moderate risk was extended eastward on the morning of April 13, and SPC forecasters contemplated issuing a high risk for portions of the area. Ultimately, however, lingering concerns about the longevity of discrete storms precluded such an upgrade. The synoptic scale setup was expected to come together as a vigorous upper-level trough pushed eastward across the Southwest United States into the Southern Plains, developing a closed 500mb low near the Dallas–Fort Worth metroplex late on April 13. At the surface, a primary area of low pressure was forecast to develop near San Angelo, Texas, supporting a trailing cold front across central Texas as well as a lifting warm front across the Ark-La-Tex region. Within the warm sector of this low- pressure system, dew points were expected to rise into the upper-60s to near 70 °F, with precipitable water values in excess of and generally low cloud bases.
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Meanwhile, a warm front was moving from Louisiana and into central and southwest Alabama. By noon, the skies had begun to darken as a cold front trailed over areas of northeast Texas. These conditions prompted the Storm Prediction Center to issue a moderate risk outlook across portions of Louisiana, Mississippi, and Alabama with a slight risk outlook covering a region from Louisiana to Tennessee, North Carolina, and Florida. The threat of severe weather across middle Tennessee was first identified by the early afternoon of January 23. A special weather statement was issued to highlight the severe weather threat for middle Tennessee for the afternoon of January 24. Another special weather statement was issued early on January 24 to continue to alert the public of the possibility of severe weather. The tornado outbreak unfolded quickly across middle Tennessee during the early afternoon of January 24. Shortly after 330 PM, Doppler radar indicated a tornado as severe weather spotters reported a funnel cloud just east of Centerville, Tennessee.
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A series of potent storm systems traversed the US during March 1913, described by the US Weather Bureau as "...the most extraordinary situation in regards to the weather since the creation of the bureau." Anomalously high moisture had gathered near the US Gulf Coast, as an intense upper level storm system moved in from the west. According to retrospective numerical modeling of this event, a strong cap aloft was in place over the central Plains, as is common as the elevated mixed layer advects eastward from the Rockies. Observations taken at 13Z 23 March 1913 showed that surface low pressure was located in Colorado, and a warm front stretched due eastward from there into Illinois. Morning temperatures near this front were in the 30s. South of the front warmer and moister air was present, but dewpoints in the upper 50s were confined to southern Oklahoma and Arkansas, far away from where the tornadoes were to later occur in eastern Nebraska and western Iowa.
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It is common as a warm front passes over an area with significant snow-pack. It is most common at sea when moist air encounters cooler waters, including areas of cold water upwelling, such as along the California coast (see San Francisco fog). A strong enough temperature difference over water or bare ground can also cause advection fog. Although strong winds often mix the air and can disperse, fragment, or prevent many kinds of fog, markedly warmer and humid air blowing over a snowpack can continue to generate advection fog at elevated velocities up to or more – this fog will be in a turbulent, rapidly moving, and comparatively shallow layer, observed as a few centimetres/inches in depth over flat farm fields, flat urban terrain and the like, and/or form more complex forms where the terrain is different such as rotating areas in the lee of hills or large buildings and so on.
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GOES-13 satellite imagery of the storm complex that produced the tornado outbreak on January 22 On January 17, 2017, the Storm Prediction Center (SPC) noted the potential for a high-end severe weather event to occur in the Southern United States on January 21 and 22. On January 20, a large-scale, negatively tilted (aligned northwest to southeast) trough moved from the Western United States over the Great Plains, Broad cyclonic flow soon became established over much of the United States, with multiple shortwave troughs embedded within. Persistent convection from the Texas coastline to Mississippi initially inhibited the northward flow of warm, moist air and by extension limited proliferation of severe thunderstorms. Later in the day, a warm front—separating moisture-rich Gulf air and modified continental-polar air—developed over the southern Mississippi Valley within an environment of steep lapse rates and modest wind shear; this became the focal point for potentially tornadic storms.
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Animation was co-opted in the 1940s for training purposes. Disney produced Four Methods of Flush Riveting for Lockheed Martin's engineers.James Algar, Walt Disney Industrial Training Film, Four Methods of Flush Riveting, 1942, Film The Army Air Force, Navy, and Bureau of Aeronautics also commissioned and supervised films. Animations were written to train pilots and ground crewmen about The Occluded Fronts,The Occluded Fronts, Bureau of Aeronautics, Walt Disney Productions, United States Navy Training Film, 1943 Thunderstorms,Bureau of Aeronautics, Walt Disney Productions, United States Navy Training Film, 1943 and The Warm Front. Because of the sensitive content displayed in Aircraft Wood Repair, the word “RESTRICTED” was the first word displayed in the film which discussed the type of glue used for wooden aircraft.Bureau of Aeronautics, Walt Disney Productions, United States Navy Training Film,Aircraft Wood Repair, 1943, Film Other films made to help train pilots included Theory of the C-1 AUTOPILOT: Part One Basic Principles which introduced pilots to the autopilot function which was new to aircraft at the time.
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With large-scale height falls, three rounds of severe weather were expected to evolve across the Midwestern United States: elevated thunderstorms across northern Illinois early in the day, significant supercell development throughout the evening and overnight hours, and a quasi-linear convective system throughout the overnight hours into March 1. At the surface, an area of low pressure developed near the Missouri–Iowa border and progressed into southern Michigan late on February 28\. A cold front, meanwhile, extended from the Plains to the Mississippi Valley, and a warm front lifted northward across Illinois. In the warm sector ahead of the cold front, rich low-level moisture surged northward, with dewpoints of 65–70 °F (18–21 °C) observed across Texas and Louisiana. Although a strong subtropical jet stream allowed a widespread cirrus plume to overspread the risk area, limiting surface heating in some locations, mid- level CAPE values were still expected to reach upward of 1500–2000 J/kg. Combined with ample moisture, steep mid-level lapse rates, and sufficient destabilization, effective bulk shear near or over 80 mph (130 km/h), was expected to yield storm relative helicity values in excess of 300–400 m2/s2.
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