Another round of arctic freeze is blasting the U.S. The first round of cold weather brought historic temperatures, with Montana’s temperatures falling to 40 to 50 degree below zero. With another round of frigid temperatures blanketing the U.S. again, what’s behind the cold?
While El Niño can be to blame for the back-to-back winter storms, something else is spurring the cold. Brad Rippey, USDA meteorologist, says moisture pumping up from the Gulf is a hallmark of El Niño.
“As I always say, you can’t blame an individual or a single storm and El Niño, but you start looking at the overall patterns, and there’s absolutely no question that when you start seeing a pattern setting up like this, a storm pipeline from the Pacific coming across the Southwest and into the Midwest or east, that is El Niño,” says Brad Rippey, USDA meteorologist.
The cold, however, is being pushed down from the north. Drew Lerner of World Weather says the arctic air is caused by a warming that occurs in the stratosphere, which is outside of where we live in the troposphere. Sudden stratospheric warming events, like what the U.S. is experiencing now, can be caused by large atmospheric waves in either the stratosphere or the troposphere. Planetary waves have ridges and troughs like ocean waves, but span huge distances in the atmosphere.
“The stratosphere, when it turns warmer, it expands that layer in the atmosphere and it pushes, puts pressure on the troposphere and forces cold air that’s aloft down to the surface. And then it gets spread out from the arctic,” says Lerner. “What happens a lot of times when you get these stratospheric warming events is that you displace the polar vortex and or you split it into two vortices, and that’s what’s happening.”
He says this can lead to a splitting of the polar vortex, so instead of cold air being locked above the polar region, it pushes further south into the mid-latitudes.
The good news? This latest round of frigid air is short-lived. The Climate Prediction Center (CPC) 10-day forecast, which is below, shows a much more mild view, at least compared to what we’re seeing now.
