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VOICE ONE:

This is Steve Ember.

VOICE TWO:

And this is Bob Doughty withSCIENCE IN THE NEWS, a VOA Special English program about recentdevelopments in science. Today, we tell you everything you everwanted to know about snow.

VOICE ONE:

Winter weather has returned to northern areas of the world. Inmuch of the United States, winter means the return of snow. Snow isa subject of great interest to weather experts. Experts sometimeshave difficulty estimating where, when or how much snow will fall.One reason is that heavy amounts of snow fall in surprisingly smallareas. Another reason is that a small change in temperature can meanthe difference between snow and rain.

VOICE TWO:

Snow is a form of frozen water. It contains many groups of tinyice particles called snow crystals. These crystals grow from waterparticles 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 depends mainly on the temperature and water levels in theair.

Snow crystals grow in one of two designs -- platelike andcolumnar. Platelike crystals are flat. They form when the airtemperature is about fifteen degrees below zero Celsius. Columnarsnow crystals look like sticks of ice. They form when thetemperature is about five degrees below zero Celsius.

VOICE ONE:

The shape of a snow crystal may change from one form to anotheras the crystal passes through levels of air with differenttemperatures. When melting snow crystals or raindrops fall throughvery cold air, they freeze to form small particles of ice, calledsleet.

Groups of frozen water droplets are called snow pellets. Undersome conditions, these particles may grow larger and form solidpieces of ice, or hail.

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VOICE TWO:

When snow crystals stick together, they produce snowflakes.Snowflakes come in different sizes. As many as one hundred crystalsmay join together to form a snowflake larger than two and one-halfcentimeters. Under some conditions, snowflakes can form that arefive centimeters long. Usually, this requires near freezingtemperatures, light winds and changing conditions in Earth'satmosphere.

Snow contains much less water than rain. About fifteencentimeters of wet snow has as much water as two and one-halfcentimeters of rain. About seventy-six centimeters of dry snowequals the water in two and one-half centimeters of rain.

VOICE ONE:

Much of the water we use comes from snow. Melting snow provideswater for rivers, electric power centers and agricultural crops. Inthe western United States, mountain snow provides up to seventy-fivepercent of all surface water supplies.

Snowfall helps to protect plants and some wild animals from cold,winter weather. Fresh snow is made largely of air trapped among thesnow crystals. Because the air has trouble moving, the movement ofheat is greatly reduced.

Snow also is known to influence the movement of sound waves. Whenthere is fresh snow on the ground, the surface of the snow takes in,or absorbs, sound waves. However, snow can become hard and flat asit becomes older or if there have been strong winds. Then the snow'ssurface will help to send back sound waves. Under these conditions,sounds may seem clearer and travel farther.

VOICE TWO:

Generally, the color of snow and ice appears white. This isbecause the light we see from the sun is white. Most naturalmaterials take in some sunlight. This gives them their color.However, when light travels from air to snow, some light is sentback, or reflected. Snow crystals have many surfaces to reflectsunlight. Yet the snow does take in a little sunlight. It is thislight that gives snow its white appearance.

Sometimes, snow or ice may appear to be blue. The blue light isthe product of a long travel path through the snow or ice. In simpleterms, think of snow or ice as a filter. A filter is designed toreject some substances, while permitting others to pass through. Inthe case of snow, all the light makes it through if the snow is onlya centimeter thick. If it is a meter or more thick, however, bluelight often can be seen.

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VOICE ONE:

Snow falls in extreme northern and southern areas of the worldthroughout the year. However, the heaviest snowfalls have beenreported in the mountains of other areas during winter. These areasinclude the Alps in Italy and Switzerland, the coastal mountains ofwestern Canada, and the Sierra Nevada and Rocky Mountains in theUnited States. In warmer climates, snow is known to fall in areasover four thousand nine hundred meters above sea level.

VOICE TWO:

Each year, the continental United States has an average of onehundred snow storms. An average storm produces snow for two to fivedays. Almost every part of the country has received snowfall at onetime or another. Even parts of southern Florida have reported a fewsnowflakes.

The national record for snowfall in a single season was set innineteen ninety-eight and nineteen ninety-nine. Two thousand eighthundred ninety-five centimeters of snow fell at the Mount Baker Skiarea in the northwestern state of Washington.

VOICE ONE:

People in many other areas have little or no snowfall. Innineteen thirty-six, a physicist from Japan produced the firstman-made snow in a laboratory. During the nineteen-forties, severalAmerican scientists developed methods for making snow in otherareas. Clouds with extremely cool water are mixed with man-made icecrystals, such as silver iodide and metaldehyde crystals. Sometimes,dry ice particles or liquid propane are used. Today, specialmachines are used to produce limited amounts of snow for winterholiday ski areas.

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VOICE TWO:

Snow is responsible for the deaths of hundreds of people in theUnited States every year. Many people die in traffic accidents onroads that are covered with snow or ice. Others die from being outin the cold or from heart attacks caused by extreme physicalactivity.

A few years ago, a major storm caused serious problems in theeastern United States. It struck the Southeast in January, ninetyninety-six, before moving up the East Coast. The storm was blamedfor more than one hundred deaths. It forced nine states to declareemergency measures.

Virginia and West Virginia were hit hardest. In some areas there,snowfall amounts were more than one meter high. Several stateslimited driving to emergency vehicles. Most major airports wereclosed for at least a day or two.

A week later, two other storms brought additional snow to theEast Coast. In the New York City area, the added weight of the snowforced the tops of some buildings to break down. Many travelers wereforced to walk long distances through deep snow to get to trainstations.

VOICE ONE:

People may not be able to avoid living in areas where it snowsoften. However, they can avoid becoming victims of wintersnowstorms.

People should stay in their homes until the storm has passed.While removing large amounts of snow, they should stop and restoften. Difficult physical activity during snow removal can cause aheart attack. It is always a good idea to keep a lot of necessarysupplies in the home even before winter begins. These suppliesinclude food, medicine, clean water, and extra power supplies.

VOICE TWO:

Some drivers have become trapped in their vehicles during asnowstorm. If this happens, people should remain in or near theircar unless they see some kind of help. They should get out and clearspace around the vehicle to prevent the possibility of carbonmonoxide gas poisoning.

People should tie a bright-colored object to the top of their carto increase the chance of rescue. Inside the car, they should open awindow a little for fresh air and turn on the engine for ten orfifteen minutes every hour for heat.

People living in areas where winter storms are likely shouldcarry 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 winteremergencies. Snow can be beautiful to look at, but it can also bedangerous.

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VOICE ONE:

This SCIENCE IN THE NEWS program was written by George Grow. Ourproducer was Cynthia Kirk. This is Steve Ember.

VOICE TWO:

And this is Bob Doughty. Join us again next week for more newsabout science in Special English on the Voice of America.