Miller: You are in Massachusetts. You've had a very snowy winter where you are in Massachusetts?
Francis: It's been quite a chilly, cold, stormy winter here.
Miller: Same here and pretty different from the last couple of winters. How is it that our weather is being affected by what's happening at the Arctic?
Francis: The difference in temperature between the Arctic and areas farther south is what drives the jet stream. The jet stream is this very fast-moving river of air over our heads that generates weather patterns and also steers them. The jet stream naturally has these north-south waves in it. As the warming in the Arctic increases faster than it does in lower latitudes, this actually tends to weaken the west-east winds in the jet stream. We know that a weaker jet stream tends to be a wavier jet stream. So those north-south waves are tending to get larger and those waves are what control our weather.
So what's happening right now is we have a big southward dip over the eastern half of the United States, and that allows the cold air from the Arctic to plunge pretty far south. And as the jet stream curves northward again along the East Coast, that tends to be a stormy pattern. Just last March, a year ago, the waves that we have now were actually shifted over to the western half of the country. In both cases, the jet stream was in this very wavy pattern that we believe is connected to the enhanced warming of the Arctic, but it was just in a different location. Both extremes — last year it was warm, this year it's cold — both can be connected to the enhanced warming of the Arctic through this enhanced waviness of the jet stream.
Miller: Just to be clear, when the jet stream sags in our area, cold air basically fills in that sagging. And that's why anything above the sagging jet stream is going to be cold in the winter.
Francis: The jet stream is basically a boundary between the colder air to the north and the warmer air to the south. So if the jet stream is to the south of you, like it is right now, then we're on the cold side.