Despite a lot of snow-melting days this month so far, the snow cover has been only sluggishly melting. One reason for this is the presence of dry air. First of all, you need to know that at the sub-microscopic level, melting snow is kind of complicated. Molecules are flying off the snow, melting into water and sublimating into vapor while vapor and liquid molecules are being re-deposited back onto the snow pack. When the air temperature is above 32 degrees, there is more melting and sublimating than there is freezing, so snow melts. But if the air is dry, the amount of molecules being condensed back into water is much higher than when the air is humid, and this condensation requires about seven times more energy than melting does. What this means is that dry air creates a thin layer of air near the snow that is much colder which keeps the snow pack colder which inhibits melting. If you want to melt snow quickly, hope for temperatures in the 30s and fog.
