Snow on the ground affects the air temperature in three basic ways.
The obvious way is that the bright, white surface of new snow is especially reflective of sunlight, and so a layer of snow reflects much of the incoming solar radiation back into space. These incoming rays offer heat as well as light. Reflected light blinds our eyes, but heat reflected back into space does not do much warming.
A less obvious way is that snow cover makes an excellent radiator of Earth’s internal heat. On a clear, calm night, the air gets cool because so much heat is radiated into space from the ground, which lowers the temperature of the air near the ground. This process is increased greatly when the ground is covered in snow.
The third way has to do with melting. When the air warms above 32 degrees, snow starts to melt. But it takes a tremendous amount of heat energy to change snow from ice to water, keeping temperatures from warming very much.
