The two key ingredients for a big snow are just cold-enough temperatures and a lot of moisture. Combine the chilled air converging on the East with the massive moisture coming from the Gulf of Mexico region and you've got the "perfect setup for a big storm," said Kevin Trenberth, of the Climate Analysis Section at the National Center for Atmospheric Research in Colorado.
As Trenberth explained, the ideal temperature for a blizzard is just below freezing -- just cold enough to crystalize water into snow. Below that, the atmosphere's ability to hold moisture to create those snowflakes drops by 4 percent for every one degree Fahrenheit fall in temperature.
"In the past, temperatures at this time of year would have been a lot below freezing," Trenberth said. In other words, it's been too cold to snow heavily. But that may become less of an obstacle for snow in the Northeast.
In addition to warming the air, climate change is adding moisture to it.
Sea surface temperatures are about two degrees Fahrenheit warmer than they were before 1980, raising the potential for a big snow by about 10 percent, according to Trenberth. And any individual storm, including this nor'easter, will pick up more moisture as it spins across a warmer ocean. What's more, as Mann explained, a warm ocean clashes with cold air masses from the Arctic. A bigger contrast in temperatures may mean a bigger storm, he said.
Michael Oppenheimer, a climate change expert at Princeton University, said global warming is increasing extreme storms. "Storms like this tend to be heavier than they used to be," he told HuffPost. "That's a fact."