Sudden and dramatic changes in high temperatures in the atmosphere dance with La Niña weather patterns. There will be no clear winner, and forecasters are still determining how cold it will be.
Something unusual may be happening in the stratosphere, and meteorologists say it could change the course of winter forecasts.
Judah Cohen, a research scientist and climatologist at the Massachusetts Institute of Technology (MIT), said in an email to USA TODAY that the atmosphere is at a “critical crossroads” and what happens in November could be a “crossroads” for the rest of the winter.
Weather models suggest that the stratosphere could suddenly warm up, causing a counterintuitive cooling effect on the Earth’s surface.
If the phenomenon of “sudden stratospheric warming” actually occurs, cold weather and snow could soon arrive in many parts of the country.
Cohen said the developments will determine how the often-misunderstood polar vortex affects U.S. weather and how cold air from the north is guided by La Niña weather patterns.
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An “extraordinary and unique event” may be underway
Mr. Cohen described a series of events that could soon occur. The stratosphere above the North Pole suddenly warms, pushing cold air south toward the United States.
This is called “sudden stratospheric warming” (SSW) and is “the biggest type of disruption that can occur in the polar vortex,” Cohen said.
“It is named after the dramatic warming that occurs in the polar stratosphere (warming near the North Pole can exceed 100 degrees in just a few days),” he said. “Warming causes the polar vortex to move much further south than normal.”
If the stratosphere suddenly warms, November would be the first such event since accurate satellite recording began, he added.
There were two known events in the pre-satellite era: November 1958 and November 1968.
“I tend not to rely on stratospheric data before satellite data was available,” Cohen says. Therefore, if a stratospheric warming event were to occur, “it would be an unusual, even unique phenomenon.”
Girl vs Polar Vortex?
If Cohen’s scenario comes true, the polar vortex would have a major impact on future weather, but as meteorologists have previously said, La Niña also has a big impact.
The relationship between the two is complex. There are no clear winners and losers as to which weather patterns will dominate the winter.
Rather, the polar vortex weather pattern largely influences the degree of coldness, Cohen said, and La Niña effects help direct that coldness.
Overall, Cohen believes that “the behavior of the polar vortex will be more influential in determining whether the U.S. experiences cold weather.”
Does cold air reach the ground?
Cohen said a key question about our weather is how strongly stratospheric warming will affect weather at the surface and in the troposphere. If the warming phenomenon were to have a strong impact on the jet stream and our weather, we would see an extended period of cold and snowy weather starting sometime in December, he said. It could also be extended into early January, “significantly increasing the likelihood of an even colder winter in the United States.”
“I believe that a weaker or short-circuited coupling between the polar vortex and the jet stream could lead to an overall warmer climate across the United States for the foreseeable future, greatly increasing the likelihood that the U.S. winter will be generally mild to very mild.”
(This story has been updated to meet our standards.)
