Next week’s cold blast will dive farther south and east.
Weather forecast models are suggesting temperatures will nose-dive in the Midwest. All of Minnesota and Wisconsin — plus the Chicagoland area — could see overnight lows plummet into negative territory: minus-15 in Minneapolis, minus-10 in Milwaukee and minus-5 in the Chicagoland area around Wednesday or Thursday.
The forecast is 20 to 35 degrees below average for this time of year.
What will likely be the coldest air since last February will barge into the Mid-Atlantic and Northeast late next week. Daytime temperatures from Washington to Boston will struggle to climb above freezing. Overnight lows will surely be in the single digits and teens, if not below zero in parts of New England.
Through Thursday, 75 percent of the Lower 48 will have experienced a temperature below freezing, including Texas, the Deep South and the Pacific Northwest, based on National Weather Service forecasts.
The frigid air tied up in this polar vortex blast has its origins in Siberia and northern Canada. It will be the coldest air of the season so far for most of the United States. Future cold blasts may be more potent, but we haven’t experienced this since last February.
The polar vortex is not a new thing — it’s a weather term that was popularized in 2014, though it’s always been something meteorologists knew of and referred to among themselves.
It’s a very large, extremely cold air mass over the Arctic (the Antarctic has one, too). The concentrated area of cold air is bound by the jet stream, which is a current of fast-moving air at very high levels of the atmosphere. When the jet stream is strong and keeps the polar vortex area bottled up north, temperatures can fall to minus-100 degrees.
The vortex is always present — even in the summer. But winter is when it really comes alive — not only is Arctic air colder because of the lack of sunlight, this is also when the jet stream plunges south. When that happens, it allows the cold air to spill south, like a freezer with the door left open.
Some of the most historic cold-air outbreaks of the past 30 years have been caused by the polar vortex diving south.