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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 ...
The warm air overrides the cooler air and moves upward. Warm fronts are followed by extended periods of light rain and drizzle due to the fact that, after the warm air rises above the cooler air (which remains on the ground), it gradually cools due to the air's expansion while being lifted, which forms clouds and leads to precipitation.
It may sometimes occur in advance of warm fronts moving northward to the east of mountainous terrain. However, precipitation along warm fronts is relatively steady, as in light rain or drizzle. Fog, sometimes extensive and dense, often occurs in pre-warm-frontal areas. [23]
Freezing rain occurs when the wedge of warm air aloft is much thicker, allowing the raindrop to survive until it comes in contact with the cold ground. A coating of ice forms on whatever the ...
However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze, and freezing rain will be the result at the surface. 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. [37]
The lack of rain in the Northeast has been rather remarkable. New York City and Wilmington, Delaware, are just two cities where only a trace of rain has fallen for the entire month of October so far.
Cold fronts form when a cooler air mass moves into an area of warmer air in the wake of a developing extratropical cyclone. The warmer air interacts with the cooler air mass along the boundary, and usually produces precipitation. Cold fronts often follow a warm front or squall line. Very commonly, cold fronts have a warm front ahead but with a ...
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 is advected aloft. [3]