Weather Whys; Frost Protection

This is weather-wise. Frost can create sparkling landscapes and paint beautiful pictures on windowpings. But to many farmers, the picture isn't so pretty. In past years, frosts have devastated over a billion dollars worth of crops, so it makes sense that frost protection is an important part of many farmers' lives. Most occurs on calm, clear nights when the temperature near the ground cools to below freezing. Moisture from the air is deposited as tiny ice crystals on leaves and on blades of grass. If the temperature gets below freezing but there's not enough moisture in the air to create frost, any plant damage is often said to be the result of a black frost. Of course, the danger to plants is the freezing of water in them, not the frost deposits on the outside. The theory behind frost protection is to change the local conditions which permit freezing. Those are the calm, clear conditions that allow heat to escape more rapidly from the

earth's surface, and that in turn make it easier for frost to develop. If there's a wind blowing or if there's cloud cover, less heat escapes into space. It's hard to create a thick layer of clouds, but it's easy to stir up a breeze. So wind machines are an important part of the frost protection arsenal. Also, keeping the air temperature warmer can help, so heaters are deployed among the trees in many orchards to help accomplish that task. In past years, the heaters were called smudge pots because of the thick black smoke they created. In fact, people thought the smoke itself trapped heat much like a layer of clouds would, but studies have shown that idea to be false and that clean burning heaters get the job done just as well. Weather-wise is made possible by a grant from the National Science Foundation. Our writer is Christine Harbor, our editor is Brian Waukey. For Weather-wise, I'm Drew Barlow.