Drawing On Science For Kids
Water droplets are always rising in the atmosphere. When the droplets get cold enough they condense (turn to a liquid) on dust, pollen grains or other small particles in clouds. When they reach a temperature of 32o F (0 o C) they begin to crystalize forming a cover of thin ice. When ice crystals form they trap air making them light and fragile. This combination of ice on dust particles forms a snow crystal. As snow crystals grow they become heavier and fall to earth. Falling crystals will combine with each other to form a snowflake. About 2 to 200 snow crystals can form a single snow flake. There is no reason why we can call a snowflake a snow crystal. They are really the same. A symmetrical, six-sided snowflake is perfectly formed. All sides are exactly alike. But most are asymmetrical (not the same on all sides).
There are four basic types of snow crystals. The shape depends on the temperature at which it was formed. The simplest type is needle-shaped, which is formed at temperatures between 27o F and 23o F . All of the other crystals have six sides. One is shaped like a six-sided, hollow column formed at tempratures between 18o F and 23 o F. One is shaped as a thin, flat six-sided plate formed at temperatures between 10o F and 18o F. And then there are very complex six-pointed star shapes formed between 3 o F and 10 o F.
Crystals grow as more and more water molecules settle on them. If a crystal has small branches sticking out, water molecules will combine with them. When more and more water molecules reach the branches they grow larger and larger. If the large branch has smaller branches the crystal becomes complex. It seems that the higher the temperature, the slower a snow crystal grows.
The many surfaces of snow crystals tend to reflect light in all directions. Our eyes see this light as white, so that snowflakes will always appear white to us. If you've ever seen glacial ice it appears blue. This is because the ice is so fully packed that there's little or no air in the crystals. When impurities in the air are trapped in the formation of snow crystals the snow will, of course, become discolored.
We all like it when it snows; especially if the weather conditions are not very severe. The life of a snowflake depends on the temperature, which must be at least 32o F both in the high atmosphere and on the ground. If the temperature is warmer near the ground the snowflakes will melt and it will rain instead. But even though snowflakes are fragile, there are times when they can be dangerous. High winds and falling snow result in a snowstorm. And when the storm is a blizzard then the danger is increased.
Blizzard conditions occur when the winds reach a speed of at least 35 mph. But the blizzard does not have to be falling snow. It can be snow that is being lifted from the ground - snow that has fallen previously. Or it can be a combination of falling and ground snow. In any case the visibility must be ¼ mile or less and the conditions must last for at least three hours.
In some areas the falling snow can reach ground layers of 3 to 6 feet. Winds can increase the depth by piling up masses of snow in selected areas.
When rain falls during conditions where the ground temperature and the air just above the ground is below freezing, the water droplets will freeze into small ice pellets before they reach the ground. This results in sleet. Freezing rain occurs when the rain water does not freeze until it actually touches the ground.
Whenever such storms or severe cold weather is predicted, you have to consider the Wind Chill Index. We experience a greater loss of body temperature on a windy, cold day than we do on a windless, cold day. This loss of temperature makes us feel colder. This is what is meant by wind chill.
Something to think about: 1) Snowflakes as large as 15 inches fell in Montana during a snow storm. 2) The average yearly snowfall in Stampede Pass, Washington is 430 inches. 3) Snowflake High School is in Snowflake, Arizona. 4) Even when snow is white and looks clean, you should not eat it. Especially if it falls in an area with air pollution. 5) Can two snowflakes be exactly the same? Studies have shown that small crystals may be alike, but larger crystals are different in shape.
Questions/comments? E-mail Steve: Drawingonscience@aol.com