Some Parts of the US May See Coldest December in Years

Bundle up, northerners. An unusual weather phenomenon unfolding high above the North Pole is expected to bring much colder temperatures than usual later this month—right after Thanksgiving—and through December, reports the Washington Post. The phenomenon, known as sudden stratospheric warming, typically happens every other winter but rarely as early as November. It involves a quick rise in temperatures and diminished winds in the stratosphere, which can disrupt the polar vortex and send frigid air plunging southward.

For now, forecasters expect below-average temperatures across parts of 35 states in the northern part of the country, according to the Post, which has a map. New England, for example, is now bracing for its coldest December in years, with temperatures 10 to 15 degrees below normal, per the Boston Globe. The particulars of how severe the cold will be, and where it will hit hardest, remain in flux, per CNN. Still, the event could wind up being the earliest major stratospheric warming on record, with only one other November instance since the 1950s. Scientists say they typically happen in January or February, when the polar vortex is more established.

"The reason we pay attention to sudden stratospheric warming events is not only because the weather impacts can occasionally be severe, but also because changes in the stratospheric winds can lead to persistent changes in weather for many weeks, giving us more time to prepare," says Amy Butler of the National Oceanic and Atmospheric Administration's Chemical Sciences Laboratory. Despite the expected year-end chill, 2025 is still on track to be one of the planet's warmest years on record.