A、Because the shape of snow crystal(晶体) is still a mystery for experts. B、Because the snowfall is a blessing for human beings. C

Winter weather has arrived in northern areas of the world. In much of the United States, winter means the return of mow. 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 panicles 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 the air. 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 mall particles of ice, called sleet.
When snow crystals stick together, they produce snowflakes. Snowflakes come in different sizes. As many as 100 crystals may join together to form a snowflake larger than two-and-one-half centimeters. Snow contains much less water than rain. About 15 centimeters of wet snow has as much water as 2.5 centimeters of rain. Each year, the continental United States has an average of 100 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.
Why are weather experts greatly interested in snow?