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| Air
masses
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Air masses have a great impact on the weather in every region.
An air mass usually has invariable temperature and humidity,
which depend on the properties of the surface of the underlying
region. This area is called a “source region”
but meteorologists agree that the territory of the United
States is not a favorable source region, as usually the air
masses do not have any opportunity to stay and acquire the
properties of a particular area.
Due to constant movement of air masses, America is famous
for storms, hurricanes and tornadoes. Usually tornadoes form
in spring, though they can happen any time throughout the
year. When the atmosphere is very unstable, cold fronts with
dry polar air meet warm fronts with moist air and it causes
hurricanes and tornadoes. For instance, last year the United
Sates experienced a tornado outbreak, which produced 105 tornadoes,
which lasted for four days, from the ninth till the thirteenth
of March. It originated in the South Central America because
of the collision of three air masses – very warm and
very humid maritime tropical air mass, very warm and dry continental
tropical air mass and very cold and very dry continental polar
air mass. The tornadoes affected the most part of Central
America and took lives of at least thirteen people.
Another phenomenon that is caused by the convergence of cold
and warm fronts is lake effect snow. It happens when cold
arctic winds shift across warmer lake water and pick up water
vapor that then chills and rests on the shores. In the United
States this is the Great Salt Lake which is very subjected
to this natural phenomenon. The lake can experience such effect
throughout the whole year, as it never freezes.
Therefore, it is obvious that the weather in the country depends
much on the circulation of air masses, which can produce different
natural phenomen
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