Dear Tom,
This week I shoveled a path through my yard and noticed that under the snow, the grass was still green and the ground soft. If the snowpack remains throughout the winter, will it prevent frost from penetrating deeply into the ground?
Rob Gabriel, Frankfort
Dear Rob,
It will, if deep snow cover remains. Climatologist Nolan Doesken at Colorado State University reports that fresh, uncompacted snow is a surprisingly good insulator because it is composed of a high percentage of trapped air–typically 90 to 95 percent. Since that air can barely move, heat transfer is greatly reduced, and a snow layer is an excellent insulator.
When snow cover deepens to 15 inches or more, its insulating qualities, coupled with the small amount of heat provided by the soil, create a temperature of about 32(degrees) where the snow and ground meet–and the ground will not freeze, even with subzero air temperatures.
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Tom Skilling is chief meteorologist at WGN-TV. His weather forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.
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