One of the most severe cold air outbreaks in years is possible from the Upper Midwest to the Northeast next week as the jet stream crashes south and a large lobe of the polar vortex plunges toward the Great Lakes.
Computer models forecast the brutal cold to crash into the Northern Plains and Upper Midwest starting Tuesday. The core of the frigid blast would grip the region from the Dakotas to the eastern Great Lakes on Wednesday and Thursday, sending cities such as Minneapolis, Des Moines, Green Bay, Milwaukee, Chicago and Detroit into a teeth-chattering freeze.
Confidence in a significant outbreak of Arctic air is high, but it’s too soon to project its exact strength and final legacy. Model predictions for the intensity of the cold snap range from historic and record-breaking to rather run-of-the-mill for midwinter.
The primary simulation from the American modeling system forecasts temperatures in the Midwest and Great Lakes next Wednesday to be 40 to 50 degrees colder than normal — which is a massive anomaly in the heart of winter when it is already very cold. Cold of this intensity would be extremely dangerous — producing widespread wind chills of minus-50 to minus-60 from Minneapolis to Chicago.
The European model also forecasts incredible cold extremes but arriving about a day later than the American model — focused on Thursday.
However, the new, experimental version of the American model suggests a less intense Arctic blast, with temperatures a more manageable but still bone-chilling 15 to 30 degrees below normal in that Wednesday-Thursday period.
Models sometimes have a tendency to exaggerate the intensity of the cold in forecasts five or more days into the future, so it is premature to predict a cold snap of historic intensity. That said, while differing on the details, models are unanimous that this will be the coldest air in the Lower 48 so far this winter.
The National Weather Service produces temperature maps that blend all of the different models together. Next Thursday morning, it projects frigid low temperatures of minus-20 to minus-30 over all of Minnesota, and minus-10 to minus-20 over northern Illinois, including around minus-15 in Chicago. Factoring in the wind, it would feel like minus-30 to minus-50 in these areas.
This model blend forecasts subzero temperatures over the entire Great Lakes region and as far south as southern Illinois to southwest Pennsylvania.
The zone from Minnesota to the Great Lakes will probably experience the brunt of this polar plunge, perhaps bleeding into the interior parts of the Northeast. By the time it reaches the Mid-Atlantic and New England on Thursday and Friday next week, its intensity should moderate. Even so, it would still be very cold — perhaps around 10 to 30 degrees below normal, depending on the cold snap’s ultimate strength.
Models predict this Arctic blast to be relatively short-lived, lasting two to three days before temperatures start returning to normal. However, reinforcing shots of Arctic air may return in the period 10 days to two weeks from now — but it is too soon to predict their potency.
Meteorologists have warned severe outbreaks of Arctic air would be possible following the early January fracture of the stratospheric polar vortex, a zone of roaring winds 60,000 feet high in the atmosphere surrounding the North Pole. Since the vortex was disrupted, it has increased north-to-south flow from the Arctic to the mid-latitudes — like a freezer door suddenly swung open.
The increase in this north-to-south flow is what will allow the polar vortex at lower altitudes (in the layer known as the troposphere, where airplanes fly and weather occurs) to drop south toward the Great Lakes next week, unleashing a sprawling plume of frigid air.