When we think of winter, we often imagine sledding, icicles and snowball fights. But think about this: winter is when earth’s north pole is tilted farther away from the sun than at any other time of the year. This is called the winter solstice, and the days just before Christmas are the shortest of all. During this time, the sun shines more directly on the lower half of the earth, or Southern Hemisphere. While we in the United States have winter, Australia, South Africa and the southern parts of South America will have summer. Because the weather continues to cool for about another month after the shortest days, the coldest weather actually arrives after the winter solstice. For most of the Northern Hemisphere, January and February are typically the coldest months.
What's Up with Winter?
During the winter we see some rain, but sometimes we see other forms of precipitation too. Winter precipitation also includes snow, sleet, and freezing rain. The type of precipitation we get depends on the temperature inside the clouds and the temperature between the clouds and the ground. In clouds that are cold enough for ice crystals to form, we can get snow. Those cold clouds aren’t hard to find. Even in the summer, most of our rain actually starts out high in the clouds as snow. But in winter, the temperature of the air is sometimes cold enough all the way from the clouds to the ground, so snowflakes don’t melt into raindrops. They stay in crystal form and we see snow pile up and schools close.
Look at the figure above. Sometimes there is a layer of air in the clouds that is above freezing, or 32 degrees F. Then closer to the ground the air temperature is once again below freezing. Snowflakes partially melt in the layer of warmer air, but then freeze again in the cold air near the ground. This kind of winter precipitation is called sleet. It bounces when it hits the ground. If snowflakes completely melt in the warmer air, but temperatures are below freezing near the ground, rain may freeze on contact with the ground or the streets. This is called freezing rain, and significant freezing rain is called an ice storm. Ice storms are extremely dangerous because the layer of ice on the streets can cause traffic accidents. Ice can also build up on tree branches and power lines, causing them to break and our lights to go out.
Until spring arrives in March, here’s wishing you a happy and safe winter!
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