Weather Talk: How snow melts is complicated
It's finally snow melting season. Although it may take a while to melt all of the snow, we all know the snow melt is inevitable. How it melts, though, is a complicated process.
Snow doesn't actually melt until the temperature of the snow rises above 32 degrees. That's why all the snow doesn't just melt away on the first warm day of spring. Surprisingly, direct sunlight only encourages melting a little, because so much of the solar radiation is reflected by the snow.
Interestingly, wind encourages snow melting on a warm day by displacing the cool air hovering against the snow with warmer air. Also interestingly, humid air melts snow faster than dry air because, at the molecular level, high humidity forces an increase in water molecules onto the still-frozen snow surface, where they refreeze. Very dry air causes snow to melt much slower.
When new snow falls in spring, it usually melts quickly because its temperature is usually near freezing as opposed to older snow that has been on the ground all winter.