NOAA's Climate Prediction Center said in its updated November outlook that a disruption of the polar vortex could occur within days, possibly developing into a sudden stratospheric warming that it called "very rare" for November, with effects that could last up to two months.

The vortex normally strengthens through the fall as the Arctic cools, holding frigid air over the pole until roughly December or January.

When it weakens, lobes of that cold air can be shoved south over North America, as happened this January, when northern Minnesota fell to -43°F and the eastern U.S. and Canada endured a deep freeze.

Experts told Scientific American the disruption may be the earliest on record, beating the previous earliest polar vortex weakening of Nov. 28, 1968.

"As a weather fan, this is a big event because it's so unprecedented," MIT climatologist Judah Cohen told the publication, adding "everybody's hair is on fire in the climate or meteorologist community."

Professor Andrew Charlton-Perez of the University of Reading said records back to satellite observations beginning in 1979 — and reasonable records to the 1940s — show no sudden stratospheric warming earlier than very late November, calling this "new territory."

The vortex must form before atmospheric waves from below can knock it into a wobble, which is why a November breakdown is so strange.

What this means for winter weather remains genuinely uncertain. A strong El Niño is in full swing — Scientific American notes there is a high chance it becomes the strongest since records began in 1950 — and it generally steers conditions milder.

NOAA's Jon Gottschalck said the combination of a strong El Niño and a westerly tropical wind pattern typically favors a stronger, more stable vortex and fewer Arctic outbreaks, though cold outbreaks should still be expected.

If the disruption takes hold, NOAA says the eastern U.S. is where effects could be felt, but El Niño's milder influence could compete against it. Charlton-Perez cautioned it is too early to say whether the record El Niño caused the event.

The stakes run in opposite directions depending on geography. In North America, a major vortex split could bring cooler temperatures in the coming weeks, though exactly when, where, or whether it happens at all is unanswered, Scientific American reports.

Cohen noted the event could end up "minor" and forgotten, or "major" and go in the record books. In the UK, Charlton-Perez said an SSW typically means colder, drier, more settled conditions; immediate snow is unlikely with summer's heat still in the oceans and land.

The bigger worry is drought: after an exceptionally dry, warm summer, some UK regions are in severe drought and need more than 120% of normal rainfall each winter month, and prolonged dry weather could stop reservoirs refilling ahead of next summer.