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air masses
AIR MASSES
Air masses form when air
lingers for days or weeks over broad expanses of land or water. Air residing
over cool water, like the Pacific Ocean, becomes cool and humid. On the other
hand, air residing over warm land, like the Columbia Basin, warms and dries.
Air masses are relatively stable and produce fair weather; on weather maps,
air masses are identified by areas of high pressure.
If you would track areas
of high pressure on a weather map, you would notice that they move. Cold, snowy
land or icy oceans, as well as tropical oceans and large deserts, are the world's
great birthplaces form air masses. Air masses carry their temperature and moisture
characteristics with them. As they migrate, they bring changing weather to regions
in their path.
The origins of air masses
and the type of surface over which they develop determine its name. Our weather
is usually dominated by a continental Polar air mass originating from central
Canada. Yet during active winter weather, the Inland Northwest can expect brief
invasions of differing air masses, such as maritime Polar and continental Tropical.
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