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In turn, precipitation can enhance the temperature and dewpoint contrast along a frontal boundary, creating more precipitation while the front lasts. Passing weather fronts often result in sudden changes in environmental temperature, and in turn the humidity and pressure in the air at ground level as different air masses switch the local weather.
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] Although, not all fronts produce precipitation or even clouds because moisture must be present in the air mass which is being lifted. [1]
The band of precipitation that is associated with their warm front is often extensive, forced by weak upward vertical motion of air over the frontal boundary which condenses as it cools and produces precipitation within an elongated band, [63] which is wide and stratiform, meaning falling out of nimbostratus clouds. [64]
An L, on the other hand, may represent low pressure, which frequently accompanies precipitation. Various symbols are used not just for frontal zones and other surface boundaries on weather maps, but also to depict the present weather at various locations on the weather map. Areas of precipitation help determine the frontal type and location.
Horizontal deformation in mid-latitude cyclones concentrates temperature gradients—cold air from the poles and warm air from the equator.. Horizontal shear has two effects on an air parcel; it tends to rotate the parcel (think of placing a wheel at a point in space and as the wind blows, the wheel rotates) and deform the parcel through stretching and shrinking.
Inversely, sometimes collapsed frontal systems will degenerate into troughs. Sometimes the region between two high pressure centers may also assume the character of a trough when there is a detectable wind shift noted at the surface. In the absence of a wind shift, the region is designated a col, akin to a geographic saddle between two mountain ...
Surface weather analyses have special symbols which show frontal systems, cloud cover, precipitation, or other important information. For example, an H may represent high pressure, implying good and fair weather. An L on the other hand may represent low pressure, which frequently accompanies precipitation. Various symbols are used not just for ...
When bands of precipitation near frontal zones approach steep topography, a low-level barrier jet stream forms parallel to and just prior to the mountain ridge, which slows down the frontal rainband just prior to the mountain barrier. [20] If enough moisture is present, sea breeze and land breeze fronts can form convective rainbands.