Snow Cover Can Have a Dramatic Effect on Temperatures

Snow cover, or lack of it, can have a dramatic effect upon temperatures.  For example,  when there is no snow on the ground at La Crosse, WI, the December daily average temperature is 10.2 degrees warmer than when there is snow (1 inch or greater) on the ground.

La Crosse, WI
(1893-2012)

  December Average
High Temp
December Average
Low Temp
December Daily 
Average Temp
No Snow Cover 35.2 F 20.7 F 27.9 F 
With Snow Cover 25.4 F 10.0 F 17.7 F
Difference 9.8 F 10.7 F 10.2 F 

Very similar results can be found anywhere in the Upper Mississippi River Valley. The images below compare the differences in the December daily average, maximum, and minimum temperatures when there was snow and no snow on the ground.

La Crosse, WI December daily maximum temperatures on average are 9.8 degrees warmer when there is no snow on the ground La Crosse, WI December daily low temperatures on average are 10.7 degrees warmer when there is no snow on the ground

La Crosse, WI December daily high temperatures
on average are 9.8 degrees warmer
when there is no snow on the ground.

La Crosse, WI December daily low temperatures
on average are 10.7 degrees warmer
when there is no snow on the ground.

Why does snow cover make a difference?

The main reason why the temperatures are usually warmer when there is no snow on the ground is that a bare ground absorbs more of the incoming solar energy (short wavelength radiation) than when the ground is snow covered.  This allows the bare ground to warm up more and in turn the air above the ground warms too; thus, warmer temperatures result. The images below show a simplified version of what occurs during the daytime.

When there is no snow on the ground, more energy from the sun can warm the ground and the air above it; thus, warmer temperatures. When there snow on the ground, more energy from the sun is reflected than absorbed by the snow.  In addition, much of the energy absored by the sun goes to melting the snow as long as the temperatures are warm enough.
When there is no snow on the ground, more energy from the sun can warm the ground and the air above it; thus, warmer temperatures. When there snow on the ground, more energy from the sun is reflected than absorbed by the snow.  In addition, much of the energy absorbed by the sun goes to melting the snow as long as the temperatures are warm enough.

Even at night, a bare ground will give off some heat (some from the heating of day and some from the Earth itself), so temperatures usually do not cool as much as when the ground is covered with a blanket of snow (insulating the relatively warm ground).  



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