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Dear
Brennan,
You're
right - it doesn't snow much in Alabama. The answer to your
question involves an introduction to the hydrologic cycle,
a discussion of types of precipitation, and then some background
on the location of Alabama.
Snow, as with all forms of water on land and in the air, is
part of the hydrologic cycle, one of the great cycles of life.
Water is evaporated from the world's oceans, stored and circulated
as water vapor in the air, and then, under certain conditions,
changes back to water droplets that form clouds. The step
that completes the cycle is precipitation, when the water
falls back to earth.
Usually precipitation falls as rain, but it can fall in other
forms, including ice, sleet and snow. Ice that forms in the
clouds and falls as lumps to the ground is called hail, and
raindrops that freeze as they fall through cold air is called
sleet. Snow takes the form of ice crystals that group into
flakes that reach the ground.
Snow crystals form in clouds when the air aloft is very cold,
well below zero, so the water vapor changes directly from
a gas to a solid as it condenses around tiny particles of
dust in the air. The shape of the snow crystal depends on
the temperature and the supply of water vapor available. If
the snow crystals fall through cold air on their way to the
ground, they may grow by bumping into other falling snow crystals
and may become as large as two inches across. If they fall
through warmer air, they melt into raindrops, or if the air
is very dry, they may evaporate before they ever reach the
ground.
Snow is common in places where winter temperatures are low,
as in the interiors of large continents. In North America,
that would be in the north central region near the Great Lakes.
Heavy snowfall often occurs here because cold, dense air originating
near the North Pole meets warm, buoyant air coming from the
Caribbean Sea. When the warm air rises and cools yet further,
heavy snowfall can result. Cities like Buffalo, New York,
are always prepared for a snowy winter.
Alabama doesn't experience cold winter temperatures very often,
so the conditions for snowfall are rarely present. The air
aloft is usually warm, and we are close to the Caribbean,
which is another source of warm air at the surface. There
is little opportunity to make snowmen or go skiing in Alabama,
but in another sense we are lucky to live in such a warm climate.
Every winter, blizzards deposit many feet of snow in the northern
United States, causing traffic accidents, power outages, and
even death. In the meantime, we can enjoy our backyard barbeque
and a dip in the pool.
Thanks
for your question,
Aubie and Dr. Martinson
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