it's so warm it's cold

Warmer water, more precipitation, more snow, colder air

Bundle Up, It’s Global Warming - NYTimes.com:

"...the overall warming of the atmosphere is actually creating cold-weather extremes. Last winter, too, was exceptionally snowy and cold across the Eastern United States and Eurasia, as were seven of the previous nine winters.

For a more detailed explanation, we must turn our attention to the snow in Siberia."