"Global warming" does not mean "end to all winter everywhere". As long as it is still cold enough to snow, warmer in winter is actually rather consistent with more snow. Just as an example take the days at Grand Forks NWS observation site from Dec-Feb this winter with at least an inch of measured snowfall and examine the temperatures of those days there. On average those ten days with >=1" of snow were about 13F warmer than the climatic normal for the date at the location.
|Day||Snow||High||Low||Diff from Avg|
At his blog, Jeff Masters has a pretty good explanation of how the recent big East Coast storms fit consistently with climate theory. Basically, warming means more moisture can be in the air to thus make big precipitation events bigger. For the normal range of observed surface air temperatures (even the wide range in North Dakota), the amount of water vapor that the air can hold approximately doubles for every 20F increase in temperature. For example, air at 5F can only hold about half the moisture of air at 25F.
A few such snowstorms this winter are not proof against global warming. To be clear, they are also not proof of global warming, and it is not appropriate to say they were caused by global warming - saying such would be incorrect. But I suspect it is much more likely that you would hear accusations that people are claiming such than it is you would actually hear those claims. Those recent storms are though completely consistent with global warming.