Miles O’Brien:

The jet stream is a river of air that flows west to east across North America. It is created by the temperature difference between warm air at the equator and cold air in the Arctic.

Some scientists suspect that, as climate change has warmed the Arctic, the temperature difference has reduced, causing the jet stream to weaken and wander. This would allow Arctic air to move farther south and linger there, creating the record cold temperatures recently in the U.S.

The arrival of the warm, moist air from the south provided the missing ingredient to create a bomb cyclone. The other factor at work here in Boston is sea level rise.