Boston Snowfall and Global Warming.

http://thinkprogress.org/climate/2015/02/12/3622201/brrrrrrrrrrrrrrrrrrrrr/

No single weather event can be attributed directly to climate change. This is common knowledge thanks in part to Kevin Trenberth, a climate scientist who’s played an integral role in explaining how to relate weather extremes to climate change. “The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question,” his most-cited quote goes. “All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.”
So if anyone tries to tell you that climate change directly caused Boston’s record-breaking and continuing snowmageddon, that’s not true. What is true, however, is that climate change may have affected the snowstorm — may have made it more likely, may have made it worse than it would have been without so much greenhouse gas in the atmosphere. It bears repeating: “All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.”
The question, then, becomes how? How did the warmer and moister environment in which we now live because of human-caused carbon emissions affect Boston’s historic weather event? Wouldn’t a warmer, moister environment mean less snow? How does that even make sense?

Trenberth, who is a senior scientist National Center for Atmospheric Research, offered his explanation via e-mail:
No doubt there is a big element of chance in having the weather pattern of the storm tracks setting up in an optimal fashion to produce big snow storms one after the after. But in mid-winter, there is plenty of cold continental air to ensure that precipitation falls as snow rather than rain.