The stratospheric polar vortex is like a vortex of cold swirling over the North Pole. The stronger it is, the faster it rotates, and the more cold air remains trapped.
But in about two weeks, weather models suggest the vortex will suddenly weaken and/or collapse. Judah Cohen, a long-range meteorologist at the Verisk Atmospheric and Environmental Research Center, told The Washington Post that the vortex disturbance would be “fairly significant.”
This means that the vortex of cold air will fill, heat and possibly displace cold air into lower latitudes.
Depending on where the Arctic cold snaps go, the stage could be set for at least one to two weeks of cold, windy weather east of the Rocky Mountains by about mid-March.
Up to this point, winter weather has been largely absent in much of the Midwest, Great Lakes, and Northeast. Snowfall has been well below normal, and so mild in some areas that the season is being described as a “lost winter.” The weather is expected to be record warm early next week, and it may end up as expected The mildest winter on record in the United States.
At the same time, the clock is ticking on how long the winter weather could last. The behavior of the vortex is all that stands between the mild weather prevailing now and the transition to spring.
How a polar vortex disturbance might unfold
Cohen said the polar vortex's disturbance may be so great that its winds will reverse — shifting from strong westerly winds to gentle easterly flow. This has not been determined yet, but the possibilities are increasing.
“A significant sudden increase in stratospheric temperature is likely to occur during the first week of March,” Simon Lee, a research scientist at Columbia University, wrote in an email. “These events lead, on average, to a negative Arctic oscillation pattern at the surface.”
The Arctic Oscillation (AO) describes the extent to which cold air is trapped in the Arctic. When the AO value is positive, this cold air remains confined to the north. When the AO flips to its negative phase, the frigid air is pushed south. Long-term weather models indicate that the Arctic Oscillation will turn negative sometime around March 7.
This season has already produced a stratospheric temperature spike and associated polar vortex disruption in January.
“What is striking is that we have a second stratospheric gyre disturbance occurring now,” Andrea Lange, a professor of atmospheric sciences at the University of Wisconsin-Madison, said in an email. “Two major polar vortex disturbances in one season is not common. It's happened before, but it's not something you'd expect to happen in any given winter season.”
She noted that when there is a sudden rise in stratospheric temperature, there is a 50 percent chance of cold air spreading somewhere in the Northern Hemisphere. A shift in the position of cold air masses can also create “storm tracks,” which favor more active weather corridors.
However, January's vortex disturbance did not lead to particularly severe winter weather in the weeks that followed.
Timing of possible return for winter
In the lead-up to the looming polar vortex disruption, the eastern United States will likely be milder From average.
“But before and during [the disruption]Cohen said that Siberia and East Asia are the regions most likely to get cold. “This is consistent with weather model predictions.”
It usually takes a week or two for the signal to translate from the upper atmosphere — known as the stratosphere, where turbulence comes as temperatures rise significantly — to the lower atmosphere, or troposphere. It would also have to start a chain reaction that would take time to reach the United States.
“The eastern U.S. often gets colder eventually, but after about two weeks,” Cohen said. “This would lead to a return of cold weather in mid-March.”
However, if the vortex becomes extended during a sudden stratospheric warming, the cold may be more pronounced. Cohen likened the expanding vortex to a rubber band, which could attract more cold air southward.
“This could lead to a faster return of cold air to the eastern U.S. and more severe cold (but not necessarily),” Cohen said. “This is something I'm watching but at the moment I don't see any signs of it in the weather models. If we get an extended PV that could be carried on the back [sudden stratospheric warming]Then cold weather could return to the eastern United States sometime during the first two weeks of March.
All of this works against the arrival of spring, where longer days, higher sun angles and general warming in the Northern Hemisphere can be an obstacle to outbreaks of cold air and snow.
“At this time of year, winter is fighting a losing battle against the monsoon cycle (and a warming climate),” Lee said. “So, while spring may start out relatively cold and wintry, the reality is that it can be difficult for this to happen [polar vortex disruption] In March doesn't mean practically the same thing as in the depths of winter.
David Toleris, a Richmond-based consulting meteorologist who provides forecasts to the public and businesses, wrote on X that he is not convinced that a polar vortex disturbance will lead to beneficial winter weather.
“I'm not saying that those who expect a late winter return in mid-March are wrong.” He said. “In fact it could happen quite a bit especially across the Great Lakes/New England and inland parts of places like New York and Pennsylvania where it could snow in late March or early April. What I'm saying is you need to take this with a great deal of skepticism.”
Jason Samino contributed to this report.
