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It forms above the mountain range, usually at the beginning of a chinook wind as a result of orographic lifting over the range. It appears when seen from downwind to form an arch over the mountain range. A layer of clear air separates it from the mountain. [3] A view of the Front Range of the Rockies capped by a föhn wall.
Continental polar air masses that affect North America form over interior Canada. Continental Tropical air masses (cT) are a type of tropical air produced by the subtropical ridge over large areas of land and typically originate from low-latitude deserts such as the Sahara Desert in northern Africa, which is the major source of these air masses.
The Bergeron classification is the most widely accepted form of air mass classification. Air mass classifications are indicated by three letters: [3] [4] Fronts separate air masses of different types or origins, and are located along troughs of lower pressure. [5] The first letter describes its moisture properties, with
A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface trough of low pressure.It often forms behind an extratropical cyclone (to the west in the Northern Hemisphere, to the east in the Southern), at the leading edge of its cold air advection pattern—known as the cyclone's dry "conveyor belt" flow.
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.
Moist air is lighter than the surrounding dry air, creating an unstable situation. When enough moist air has accumulated, all the moist air rises as a single packet, without mixing with the surrounding air. As more moist air forms along the surface, the process repeats, resulting in a series of discrete packets of moist air rising to form ...
Occluded fronts usually form around mature low pressure areas.There are two types of front occlusions, warm and cold, depending on the temperature contrast: . In a cold occlusion, the cold air mass that overtakes the warm air mass ahead is colder than the cool air at the very front and plows under both air masses, and often has the characteristics of a cold front.
Temperature inversion in an urban environment Temperature inversion in the Lake District, England, forms clouds at a low level under clearer air. Smoke rising in Lochcarron, Scotland, is stopped by an overlying layer of warmer air (2006). Smog trapped over the city of Almaty, Kazakhstan during a temperature inversion.