WaPo: 'For now, the consensus view still holds that global warming will bring fewer cold snaps to places like the U.S., not more. The IPCC in 2007 predicted that there was 'likely to be a decline in the frequency of cold air outbreaks... in [northern hemisphere] winter in most areas.'
'There is a theory for how global warming could cause severe cold in the U.S. — but it's still heavily debated. Right now, the Arctic region is warming rapidly. And a few scientists think this could cause the jet stream to slow down and weaken and meander all over the place more often. This is a relatively new idea, and there's still a whole lot of debate over the link between Arctic warming and extreme weather. Jennifer Francis of Rutgers sketched out the theory here. In August, Elizabeth Barnes of Colorado State disputed the link (and Francis responded here).