Temperatures at the high altitudes above the North Pole are soaring, jumping up to 50 degrees in barely a week. The so-called “sudden stratospheric warming” is disturbing the polar vortex, which in turn could have major implications for weather patterns across the northern hemisphere in March.
There has been some speculation that the current event could topple the first domino in a chain reaction that would reshuffle weather patterns. For instance, the eastern U.S. has seen an exceptionally mild January and February and some previous sudden stratospheric warming and polar vortex disruptions have precipitated extreme cold snaps and severe winter storms.
Andrea Lang, a researcher at the University of Albany, wrote in an email that polar vortex disruptions have been known to result in “a 50% increase in cold air outbreaks in the northern hemisphere and a shift in the storm tracks.”
The last time a sudden stratospheric warming event occurred was Jan. 5, 2021. Just over a month later, the most dramatic cold air outbreak since 1989 plunged the central U.S. into a historic deep freeze, causing the collapse of Texas’s power grid, claiming at least 330 lives and incurring more than $27 billion in damages.
But multiple experts interviewed about the ongoing event say it’s too soon to know whether this one will trigger extreme weather or meaningfully change prevailing weather regimes over the northern hemisphere.
Explaining a sudden stratospheric warming event
What is the stratosphere?
To understand these events, we first have to ask “what is the stratosphere?”
We live in the troposphere, or the lowest level of earth’s atmosphere. Weather predominantly occurs in the troposphere. Above the troposphere lies the stratosphere, which begins between 5 and 12 miles above the ground. Air temperature decreases with height in the troposphere (that’s why airplane windows always feel cold, even in the heart of summer), but increases with altitude in the stratosphere. Thunderstorm anvil clouds flatten out when updrafts hit the boundary between the troposphere and the stratosphere. Meteorologists refer to that as the tropopause.
What’s the polar vortex?
You’ve probably heard of the term “polar vortex” before, but referring to a singular polar vortex is a bit of an oversimplification. Both the troposphere and stratosphere each have a polar vortex. The troposphere’s is present year-round, tends to be more chaotic and is encircled by the jet stream.
The stratospheric polar vortex is smoother, smaller and more circular. It doesn’t exist year-round — instead it’s a whirlpool of frigid air that forms in the fall as the upper atmosphere cools. The bone-chilling, dense air sags downward as its density increases, creating a void in the upper atmosphere that pulls air inward in a counterclockwise fashion. That vortex persists until the atmosphere warms in the spring.
What causes a sudden stratospheric warming?
A sudden stratospheric warming ensues when air temperatures in the stratosphere rapidly increase. That can come from a disruption to the stratospheric polar vortex. Jarring the vortex through large-scale atmospheric waves (sprawling mid-latitude weather systems) that get reflected upward into the stratosphere can be a cause.
Picture a spinning top. It can whir and gyrate unimpeded when left in steady-state (unbothered), but if you jiggle the table or blow on it, any subtle perturbation can knock it off-kilter and send it spiraling into demise. The stratospheric polar vortex is similar.
What does sudden stratospheric warming do to the polar vortex?
During a sudden stratospheric warming event, the westerly winds that make up the vortex can slow or even reverse direction. Such a reversal has occurred with the current event.
“The westerly winds [in the extreme upper atmosphere] and 60°N have reversed to easterlies,” wrote Simon Lee, an atmospheric scientist at Columbia University, in an email. “It is a displacement event, with the vortex nudged off the pole toward Eurasia.”
Imagine you’re stirring a cup of coffee. As you stir faster, the depression in the middle gets deeper. But if you stop stirring, the depression flattens as the vortex “fills in.” Same thing here. As the polar vortex fills in, cold air can be displaced from the pole to the mid-latitudes, with frigid Arctic blasts sometimes reaching Europe, North America and/or Asia.
How could it affect the weather?
Lee explained that a sudden stratospheric warming “is not a binary event like a flicked switch,” and instead the ongoing episode could be reinforced in the weeks ahead.
“Forecasts suggest that this sudden stratospheric warming will continue to evolve over the coming weeks, with [westerly] winds appearing likely to decelerate twice in a ‘double-dip’,” he wrote. “Such an evolution is fairly common in major [events].”
Until it’s clear exactly how the sudden stratospheric warming will evolve, meteorologists can’t make judgment calls about how it could impact the weather.
“How the disrupted vortex evolves and interacts with waves moving up from the troposphere in the coming two weeks will be important in determining the extent to which it can influence tropospheric weather,” Lee concluded.
Lang said that this sudden stratospheric warming event could be particularly long-lived.
“What is interesting about this event is that we are not looking at a short-lived reversal of the stratosphere’s high-latitude circulation,” she wrote. “This event is forecast to persist for at least a week to 10 days.”
Moving into March, the stratospheric polar vortex tends to weaken anyway. If this ongoing event precipitates the “end of season” disruption of the stratospheric polar vortex, it would be very unusual. The annual springtime demise of the polar vortex is known as a “final warming,” according to Judah Cohen, a seasonal forecaster with Atmospheric and Environmental Research.
A mid-February final warming “would be weeks earlier than any previously observed,” Cohen said in a message.
That doesn’t necessarily correspond to a bigger impact, though.
“The longer the [polar vortex] is disrupted and does not recover, [the longer] it delays impacts on our weather,” Cohen said.
If the impacts hold off until March, as Cohen pointed out, any uptick in wintry weather would be combated by increasing sunshine and the seasonal increase in temperatures.
Lang said not to expect big changes to the weather in the short-term by the radical changes occurring high above our heads.
“Right now, the forecast is suggesting that the immediate impacts of this sudden stratospheric warming event on our weather will be minimal,” she said.
Jason Samenow contributed to this report.