Snow is nature's refrigerator. In fact, in places where snow can fall, record cold temperatures inevitably occur when there is snow cover.
So why does snow produce cold surface air temperatures? And remember surface air temperatures are measured at 2 meters above the ground level.
First, snow is highly reflective, allowing it to reflect the warming rays from the sun back to space.
Second, snow is a very good EMITTER of infrared radiation, much better than the atmosphere. Such emission of infrared radiation to space produces substantial cooling...think of a refrigerator coil at the surface.
OK, so snow prevents the sun's rays from warming and snow cools by emitting infrared radiation.
But there is more Snow is a good insulator. The ground and particularly the subsoils can be relatively warm. So the snow prevents the conduction of heat from below. That contributes to cooling.And finally, if air temperatures get above freezing, melting snow stays at 32F until it gone.