A record-early disruption of the polar vortex has sent Arctic air plunging across the eastern United States, and a second wave of cold could arrive by Thanksgiving.
On November 11, the winds of the stratospheric polar vortex, a vast current of cold, low-pressure air circling the North Pole, reversed direction in a phenomenon known as a major sudden stratospheric warming event. It struck roughly two and a half weeks earlier than any such disruption since modern records began in 1958.
The vortex normally traps frigid air near the Arctic, but a sudden warming can distort it and let that cold spill south into the mid-latitudes. That shift left much of the East markedly colder this week, and a nor'easter delivered the season's first significant snow to some higher elevations.
Forecast models now point to another drop in temperatures and a renewed chance of snow around Thanksgiving, though the severity remains uncertain and hinges on how the disruption unfolds over the next two weeks.
Major sudden stratospheric warmings usually arrive in January or February, and this record-early timing has no clear precedent. A strengthening El Nino, already among the strongest on record, may be fueling the breakdown, but with no comparable event in the historical record, forecasters face an unusually difficult read on what comes next.