Via Phil Plait:

Record snow in a warming world? The science is clear

Super-saturated air
The science behind this is clear: Warmer temperatures cause more water to evaporate into the atmosphere, and warmer air holds more water than cooler air. The air’s “water-holding capacity,” in fact, rises about 7 percent with each Celsius degree of warming. This results in air that becomes super-saturated with water, often bringing drenching rainfall followed by flooding or – if it is cold enough – heavy and intense snowfall.