A sudden stratospheric warming (SSW) event is forecasted to hit in the coming weeks, disrupting the beginning of spring.

SSWs occur once every two years when the stratosphere suddenly warms by up to 122 degrees Fahrenheit in a week.

The stratospheric polar vortex—winds that flow from the Arctic, from west to east—also rapidly reduces in speed, or can even reverse in direction. And when the vortex is disrupted, this can lead to a dramatic change in temperatures and weather patterns, even if this phenomenon happens many miles above us.

Amy H. Butler, an atmospheric scientist at the National Oceanic and Atmospheric Administration (NOAA) Chemical Sciences Laboratory in Colorado, told Newsweek: "What causes these events is very large atmospheric waves. Low and high pressure systems on weather maps are manifestations of these waves. But, during winter, these waves can sometimes amplify into the stratosphere, the region above where our weather occurs.

"Just like ocean waves on a beach, these atmospheric waves then sometimes break, depositing huge amounts of momentum and heat. This is what causes the polar vortex winds to slow down and the stratosphere to warm."

The warming event is likely to shift the jet stream to the south. This would see cold weather spill into northern Europe, parts of Asia, and the eastern United States. Most of the latter region has seen milder temperatures this winter, with the exception of some brief blasts from the Arctic.

"Current forecasts for this upcoming event have temperatures in some portions of the stratosphere going from around -40 F to 32 F over the course of four days," Zachary Lawrence, a research scientist for NOAA, told Newsweek.

Due to the timing of this, it is likely to have an impact on the start of spring.

"With this SSW occurring in mid-February, the typical time lag of a few weeks for the troposphere to really feel the SSW means this event could influence the onset of spring for the eastern U.S.," Lawrence said.

"The eastern U.S. has experienced a rather warm winter (to many people's dismay), so it is possible that a cooler start to spring is in the cards. Depending on who you ask, this could mean a kind of 'more of the same' (conditions that are warm for winter, but cool for spring)."

Although these events occur every two years, no two are exactly the same, meaning that, though scientists can guess, it is hard to know exactly what will occur.

Butler said this phenomenon is similar to stirring a coffee cup. "If you stir it all in one direction, the coffee at the top and bottom both move together in the same direction. But then, if you put a spoon into just the top surface, the coffee at the top will slow down and start spinning in swirls, but the coffee even at the bottom will start to slow down.

"This is obviously not a perfect analogy for our atmosphere but gives you an idea of how the slowing down of winds at the top of our atmosphere could be connected to winds lower down," Butler said.

"Other regions actually see increased chances of warmer-than-average temperatures, such as parts of subtropical Africa and Asia. However, this is a 'probabilistic' forecast. The SSW loads the dice for these weather patterns to occur for several weeks. But it's difficult to otherwise pinpoint it further to say it will cause, for example, a certain snowstorm in a certain location."

Scientists can learn more about these weather events by analyzing past SSWs that have taken place.

An SSW in 2021 saw the eastern U.S. warm at the beginning of January. Then, 20 days later, temperatures dropped dramatically and cold weather spread throughout the region. It lasted for about one month, research from The Washington Post reported.

The polar vortex can cause a lot of the strange weather being seen in the U.S. and other parts of the world.

Some scientists believe that climate change has caused the vortex to be more disrupted than normal. The warming temperatures can cause this to move in different ways.

When the polar vortex is not disrupted, it circulates air from west to east, which separates cold air in the north from the milder south.

However, warming temperatures may disrupt this flow, causing the polar vortex to become less stable. This is an unconfirmed theory, but disruptions in the vortex have correlated with warming temperatures over the past few decades.

"Weather systems and wiggles in the jet stream within the troposphere cause waves that propagate vertically into the stratosphere where they batter against the stratospheric polar vortex," Lawrence said.

"Over time, this can weaken the vortex, making it easier for these waves to deliver a 'knockout.' An imperfect analogy is to think of it like waves on a beach. As waves break on shore, they can erode the coastline (the polar vortex). When you add it up over time, or you get really big waves, you can cause a collapse."

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about the sudden stratospheric warming? Let us know via science@newsweek.com.

Correction 2/13/23 9:02 a.m.: This article was corrected to say some portions of the stratosphere may go from around -40 F to 32 F over the course of four days, meaning a rise, not a drop.

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