A rare phenomenon could influence the weather later this month with a blast of cold that could drop temperatures below average across parts of the U.S.
Why It Matters
Forecasters are monitoring a rare atmospheric event known as sudden stratospheric warming (SSW), expected to significantly disrupt the polar vortex in late November or early December. Such events can shift weather patterns across the United States by destabilizing the polar vortex high above the North Pole, potentially allowing frigid Arctic air to surge into North America.
What To Know
This year’s anticipated SSW is remarkable for both its timing—potentially the earliest in nearly three decades—and for its implications, fueling uncertainty for communities and industries preparing for the winter season. A combination of SSW and the ongoing La Niña weather pattern may further complicate forecasts for the months ahead.
“Whenever there’s one of these, it usually means a weakening of the polar vortex, which means…it gets cold in the mid-latitudes,” National Weather Service (NWS) Weather Prediction Center meteorologist David Roth told Newsweek, adding that cold outbreaks could begin for the Upper Midwest and Plains states beginning on Thanksgiving.
The polar vortex, a persistent area of low pressure high in the stratosphere above the Arctic, plays a critical role in winter weather patterns. Normally, a strong, stable polar vortex helps keep the coldest air over the Arctic. But when a major SSW disrupts the vortex, it can become elongated, displaced or even split apart, resulting in the release and southward movement of frigid air masses. This phenomenon can produce exceptional cold snaps and spikes in snowy weather across the United States and Europe.
This year, the polar vortex is projected to weaken and be displaced from the North Pole as early as late November. Records dating to the late 1950s show only two major SSWs of this magnitude occurring in November of 1958 and 1968. Meteorological data hints that the atmospheric disruption could set the stage for an extended period of colder-than-normal temperatures, especially for the Midwest, Plains and Ohio Valley regions, starting in late November. However, the exact duration and location of impacts remain uncertain.
Sudden stratospheric warming events can raise stratospheric temperatures by as much as 70 degrees Fahrenheit in just a few days. This rapid warming disrupts normal wind patterns, ultimately weakening the polar vortex and allowing the jet stream to move more erratically. As a result, cold Arctic air may spill into lower latitudes, bringing abrupt and severe cold waves. Past SSW events have triggered record-breaking cold spells and significant winter storms in the United States, such as the cold outbreaks during late December 2016.
While a weakened polar vortex historically raises the likelihood of cold-air outbreaks across the United States, the pattern can be difficult to predict. Factors such as the strength of the SSW, the atmospheric response and the concurrent influence of La Niña and Pacific marine heat waves will determine how extreme or persistent chilly conditions become.
What People Are Saying
NWS Climate Prediction Center: “La Nina, the Madden-Julian Oscillation (MJO), and the potential for a rare November Sudden Stratospheric Warming (SSW) may combine to drive winter-like conditions across much of the U.S.
“Below normal temperatures are favored for the Central and Northern U.S., including northern parts of the Pacific Northwest, the Great Plains, parts of Texas, and the interior Mid-Atlantic. Below normal temperatures may start as early as November 25 (see prior forecasts), with spatial coverage and confidence increasing during the Nov 26-30 period.
Cooler temperatures are forecast to persist into early December. Below normal temperatures remain across the Northern Tier and Great Plains and expand eastward to the Northeast coast.”
What Happens Next
Meteorologists encourage Americans to monitor local winter forecasts in the coming weeks and remain alert for updated guidance, especially those in the central and midwestern states. Sudden shifts in the jet stream can also lead to increased chances of significant snowstorms.
With SSWs among the most consequential winter weather phenomena, preparedness and timely information are key for residents, businesses and emergency managers. As the stratospheric event unfolds, its real-world impacts will become clearer, but the potential for a frigid and dynamic early winter is higher than in recent years.
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