SCIENCE REPORT
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January 16, 2002: Snow Facts
By George Grow
This is the VOA Special English SCIENCE REPORT.
Winter weather has arrived in northern areas of the world. In much of the United States, winter means the return
of snow. Last month, during a severe storm, about two meters of snow fell on the city of Buffalo, New York.
Snow is a subject of great interest to weather experts. Experts sometimes have difficulty
estimating where, when or how much snow will fall.
Snow is a form of frozen water. It contains many groups of tiny ice particles, called snow
crystals. These crystals grow from water particles in cold clouds. They usually grow around a
piece of dust. All snow crystals have six sides, but they grow in different shapes. The shape Snow storm in
depends mainly on the temperature and water levels in the air. Buffalo
Snow crystals grow in one of two designs --platelike and columnar. Platelike crystals are flat. They form when
the air temperature is about fifteen degrees below zero Celsius. Columnar snow crystals look like sticks of ice.
They form when the temperature is about five degrees below zero Celsius.
The shape of a snow crystal may change from one form to another as the crystal passes through levels of air with
different temperatures. When melting snow crystals or raindrops fall through very cold air, they freeze to form
small particles of ice, called sleet.
When snow crystals stick together, they produce snowflakes. Snowflakes come in different sizes. As many as
one-hundred crystals may join together to form a snowflake larger than two-and-one-half centimeters. Snow
contains much less water than rain. About fifteen centimeters of wet snow has as much water as two-and-one-half
centimeters of rain. About seventy-six centimeters of dry snow equals the water in two-and-one-half centimeters
of rain.
Each year, the continental United States has an average of one-hundred snow storms. An average storm produces
snow for two to five days. Almost every part of the country has received snowfall at one time or another. Even
parts of southern Florida have reported a few snowflakes.
Snow creates many problems for people traveling. But it also is important. Much of the water we use comes from
snow. Melting snow provides water for rivers, electric power centers and agricultural crops. In the western
United States, mountain snow provides up to seventy-five percent of all surface water supplies.
This VOA Special English SCIENCE REPORT was written by George Grow.
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