A critical blockade against some of nature’s coldest air has temporarily broken down far earlier than normal. The polar vortex, a band of upper-level winds wrapping around the Arctic Circle like a dam, began reversing on Tuesday and computer model guidance expects that reversal to last through Thursday.
That is why Polar Vortex El Niño Winter Weather is getting attention now. The breakdown is unprecedented this early in the historical record, and disruptions of this extent usually do not happen until the latter half of winter. When the circulation weakens or reverses, it can set off an atmospheric chain reaction that pushes intensely cold air out of the Arctic toward lower latitudes.
The timing matters because the season is already being shaped by the strongest El Niño on record. Much of North America can expect warmer-than-normal conditions during a winter dominated by a strong El Niño, but that broad signal does not erase the chance that bitterly cold air spills southward if the polar vortex disruption sends it that way. The result is a forecast that can swing between warmth and deep cold, depending on where the Arctic air ends up.
There is still a catch. Weather patterns take a few weeks to respond to a polar vortex disruption, if at all, and reliable forecasts only reach about 10 days into the future. That leaves the exact path of any cold outbreak uncertain, even if the circulation breakdown itself is clear. The question now is not whether the vortex has wobbled, but where the cold air goes next.
History shows why forecasters are watching closely. A highly disrupted polar vortex in early 2015 sent a weeks-long burst of cold air over the eastern US. Chicago recorded its coldest February in nearly 140 years, and In Lexington, Kentucky, temperatures bottomed out at -18 degrees Fahrenheit. This event is arriving much earlier than that one, which makes the next few weeks the part of the season that matters most.
