Yesterday's snow storm provided an opportunity to test the insulating effect of snow on the ground. I had always heard that snow was a good insulator and thus protected the animals and the plants on or in the soil against very low temperatures. But I had no idea how effective it really was until last night when I went out and took some temperature measurements.
The red curve is the air temperature a few cm above the snow surface between 18:50 and 23:30 and the blue curve is the temperature ~18 cm below the snow*. So the temperature above the soil was just below freezing and quite stable during the 4.5-h period when the air temperature went down more than 3.5 degrees to -9.2 °C.
At the end I noticed that at some spots under the snow the temperature was actually above freezing; the highest temperature I measured was +1.2 °C. I was taking these measurements near a snow-covered rock that had been in the sun during the afternoon. Perhaps, the temperature was higher near the rock than it was at points away from it (those are the rocks where the tiny snail Vertigo pygmaea survives the winter).
I am starting to realize that "climate", especially in terms of temperature and humidity, is a highly variable phenomenon at a scale of meters or less.
Here is an information sheet on temperature under snow from 1935.
*Temperatures were measured with a thermistor. Depth of the snow at the location was ~18 cm.