If you’re wondering what happened to winter, you’re not alone.
The first two months of winter – December and January – were the warmest on record across the U.S., the National Oceanic and Atmospheric Administration says.
In fact, dozens of cities east of the Mississippi River were reporting one of their warmest winters to date from Dec. 1 through Feb. 17, according to the Southeast Regional Climate Center.
And all of the big cities of the Northeast and mid-Atlantic, from Boston to Washington, D.C., have seen less snow than usual.
We can thank an unusually strong polar vortex for our mild winter: It kept the arctic air locked in across the polar regions rather than plunging southward into the U.S., the Weather Channel said.
The polar vortex – everyone’s favorite wintertime whipping boy – is a large area of cold air high up in the atmosphere that normally spins over the North Pole (as its name suggests). The stronger the polar vortex, the milder our winter is.
“The polar vortex is near record strong and little change is predicted for the foreseeable future,” tweeted meteorologist Judah Cohen of Atmospheric and Environmental Research this week.
Sometimes, however, thanks to a meandering jet stream, a part of the vortex can slosh down into North America, helping to funnel unspeakably cold air down here where we all live. That hasn’t happened yet this winter.
The #polarvortex (PV) is near record strong and little change is predicted for the foreseeable future. But even with a strong PV, which regions could see a pattern change from the overall mild #winter pattern and which regions are unlikely to see one: https://t.co/mcVH8RLp5d pic.twitter.com/wwXLzr3AwR
— Judah Cohen (@judah47) February 17, 2020
So why has it stayed up there this winter? In part, it’s because the polar vortex has kept the “Arctic Oscillation” – a large-scale climate pattern – in its positive phase for most of the winter.
The two phenomena go hand-in-hand: The Arctic Oscillation is positive because the polar vortex is strong.
Thus, during a positive Arctic Oscillation the jet stream flows in a more orderly straight line, as opposed to an undulating pattern that would allow Arctic air to seep south.
However, there are signs that some colder air from Canada will make its way down to the eastern U.S. later next week and into early March, according to Cohen, who said it’s “related to a minor disruption of the polar vortex.”
So don’t put away those winter coats and hats just yet.
Contributing: Kimberly Miller, the Palm Beach Post
Possibly the most positive 5-day period of Arctic Oscillation you have ever seen.
Anomalously low pressures inside the Arctic circle, surrounded by high pressures at mid-latitudes all over the globe. pic.twitter.com/T93q8EoJ9p
— Mika Rantanen (@mikarantane) February 19, 2020
This article originally appeared on USA TODAY: Polar vortex: First 2 months of winter were warmest on record in U.S.