This is SCIENCE IN THE NEWS in VOA Special
English. I'm Shirley Griffith.
And I'm Steve Ember. Today, we tell you everything you ever wanted
to know about snow.
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Winter weather has returned to northern
areas of the world. In much of the
United States, winter means the return of snow. Snow is a subject of great interest to weather experts. Experts sometimes have difficulty estimating
where, when or how much snow will fall. One reason is that heavy amounts of snow fall in surprisingly small
areas. Another reason is that a small
change in temperature can mean the difference between snow and rain.
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
snow crystals have six sides, but they grow in different shapes. The shape depends mainly on the temperature
and water levels in the air. 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.
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.
Groups of frozen water droplets are called snow
pellets. Under some conditions, these
particles may grow larger and form solid pieces of ice, or hail.
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. Under some conditions,
snowflakes can form that are five centimeters long. Usually, this requires near freezing
temperatures, light winds and changing conditions in Earth's atmosphere.
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.
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.
helps to protect plants and some wild animals from cold, winter weather. Fresh snow is made largely of air trapped
among the snow crystals. Because the air
has trouble moving, the movement of heat is greatly reduced.
Snow also is known to influence the movement of sound
waves. When there is fresh snow on the
ground, the surface of the snow takes in, or absorbs, sound waves. However, snow can become hard and flat as it
becomes older or if there have been strong winds. Then the snow's surface will help to send
back sound waves. Under these
conditions, sounds may seem clearer and travel farther.
Generally, the color of snow and ice appears
white. This is because the light we see
from the sun is white. Most natural
materials take in some sunlight. This
gives them their color. However, when
light travels from air to snow, some light is sent back, or reflected. Snow crystals have many surfaces to reflect
sunlight. Yet the snow does take in a
little sunlight. It is this light that
gives snow its white appearance.
snow or ice may appear to be blue. The
blue light is the product of a long travel path through the snow or ice. In simple terms, think of snow or ice as a
filter. A filter is designed to reject
some substances, while permitting others to pass through. In the case of snow, all the light makes it
through if the snow is only a centimeter thick. If it is a meter or more thick, however, blue light often can be seen.
falls in extreme northern and southern areas of the world throughout the
year. However, the heaviest snowfalls
have been reported in the mountains of other areas during winter. These areas include the Alps in Italy and
Switzerland, the coastal mountains of western Canada, and the Sierra Nevada and
Rocky Mountains in the United States. In
warmer climates, snow is known to fall in areas over four thousand nine hundred
meters above sea level.
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year, the continental United States has an average of one hundred
snowstorms. An average storm produces
snow for two to five days.
every part of the country has received snowfall at one time or another. Even parts of southern Florida have reported
a few snowflakes.
national record for snowfall in a single season was set in nineteen
ninety-eight and nineteen ninety-nine. Two thousand eight hundred ninety-five centimeters of snow fell at the
Mount Baker Ski area in the northwestern state of Washington.
People in many other areas have little or no
In nineteen thirty-six, a
physicist from Japan produced the first man-made snow in a laboratory. During the nineteen-forties, several American
scientists developed methods for making snow in other areas. Clouds with extremely cool water are mixed
with man-made ice crystals, such as silver iodide and metaldehyde
Sometimes, dry ice particles
or liquid propane are used. Today,
special machines are used to produce limited amounts of snow for winter holiday
Snow is responsible for the deaths of hundreds of
people in the United States every year. Many people die in traffic accidents on roads that are covered with snow
Others die from being out in the cold or from
heart attacks caused by extreme physical activity. Last month, two major snow storms caused
serious problems in most of the United States. In the East, one storm dropped lots of snow on communities from North
Carolina to the New England states on the weekend before Christmas. The Associated Press reported that at least
seven deaths were linked to the storm. Most
involved automobile accidents.
caused cancellation of thousands of flights along the East Coast. About one thousand two hundred flights were
cancelled at New York City's three major airports.
storm gave two airports in the Washington, D.C. area their highest one-day
snowfall totals for December. The most
snowfall was reported in nearby Wintergreen, Virginia, where more than
seventy-six centimeters fell. And, the
city of Philadelphia, Pennsylvania received its second-biggest snowfall since
may not be able to avoid living in areas where it snows often. However, they can avoid becoming victims of snowstorms. People should stay in their homes until the
storm has passed. While removing large
amounts of snow, they should stop and rest often. Difficult physical activity
during snow removal can cause a heart attack.
It is always a good idea
to keep a lot of necessary supplies in the home even before winter begins. These supplies include food, medicine, clean
water, and extra power supplies.
drivers have become trapped in their vehicles during a snowstorm. If this happens, people should remain in or
near their car unless they see some kind of help. They should get out and clear space around the
vehicle to prevent the possibility of carbon monoxide gas poisoning.
People should tie a
bright-colored object to the top of their car to increase the chance of
rescue. Inside the car, they should open
a window a little for fresh air and turn on the engine for ten or fifteen
minutes every hour for heat.
living in areas where winter storms are likely should carry emergency supplies
in their vehicle. These include food,
emergency medical supplies, and extra clothing to stay warm and dry. People in these areas should always be prepared
for winter emergencies. Snow can be
beautiful to look at, but it can also be dangerous.
SCIENCE IN THE NEWS was written by George Grow. Our producer was Brianna Blake. I'm Shirley Griffith.
I'm Steve Ember. You can comment on our
stories at our Web site, voaspecialenglish.com. Join us again next week for
more news about science in Special English on the Voice of America.