U.S. winter storm lull to be followed by Arctic blast

Winter is normally cold, but starting Sunday tundra-like temperatures are poised to deliver a rare and potentially dangerous sledgehammer blow to much of the U.S. Midwest, driving temperatures so far below zero that records will shatter.

One reason? A "polar vortex," as one meteorologist calls it, which will send cold air piled up at the North Pole down through Canada to the U.S., funnelling it as far south as the Gulf Coast.

The temperature predictions are startling: –31 C in Fargo, N.D., –35 C in International Falls, Minn., and –26 C in Indianapolis and Chicago. At those temperatures, exposed skin can get frostbitten in minutes and hypothermia can quickly set in because wind chills could feel like 45, 50 or even 55 below zero.

Record-breaking cold

Temperature records will likely be broken during the short yet forceful deep freeze that will begin in many places on Sunday and extend into early next week. That's thanks to a perfect combination of the jet stream, cold surface temperatures and the polar vortex — a counterclockwise-rotating pool of cold, dense air, said Ryan Maue, of Tallahassee, Fla., a meteorologist for Weather Bell.

"All the ingredients are there for a near-record or historic cold outbreak," he said. "If you're under 40 [years old], you've not seen this stuff before."

Snow already on the ground and fresh powder expected in some places ahead of the cold air will reduce the sun's heating effect, so nighttime lows will plummet thanks to strong northwest winds that will deliver the Arctic blast, Maue said. And there's no warming effect from the Gulf to counteract the cold air, he said.

The cold blast will sweep through parts of New England, where residents will have just dug out from a snowstorm and the frigid temperatures that followed. Parts of the central Midwest could also see up to a foot of snow just as the cold sweeps in pulling temperatures to –23 C in the St. Louis area.

Even places accustomed to normally mild to warmer winters will see a plunge in temperatures early next week, including Atlanta where the high is expected to hover a few degrees below freezing on Tuesday.

"This one happens to be really big and it's going to dive deep into the continental U.S. And all that cold air is going to come with it," said Sally Johnson, meteorologist in charge at the National Weather Service in Sioux Falls.

It's relatively uncommon to have such frigid air blanket so much of the U.S., maybe once a decade or every couple of decades, Maue said. But in the long-run the deep temperature dives are less meaningful for comparison to other storms than daytime highs that are below zero and long cold spells, he said.

And so far, this winter is proving to be a cold one.

"Right now for the winter we will have had two significant shots of major Arctic air and we're only through the first week of January. And we had a pretty cold December," Maue said.

Schools to stay closed

Cities and states are already taking precautions. Minnesota called off school for Monday statewide, the first such closing in 17 years, because of projected highs in the minus teens and lows as cold as -34 C. Milwaukee and Madison, Wis., students also won't be in class Monday. North Dakota Gov. Jack Dalrymple urged superintendents to keep children's safety in making the decision after the state forecast called for "life-threatening wind chills" through Tuesday morning.

Sunday's playoff game in Green Bay could be among one of the coldest NFL games ever played. Temperatures at Lambeau Field are expected to be a frigid minus –18 C when the Packers and San Francisco 49ers kick off, and by the fourth quarter it'll be a bone-chilling –21 C, with wind chills approaching –34 C, according to the National Weather Service. Officials are warning fans to take extra safety measures to stay warm including dressing in layers and sipping warm drinks.

And though this cold spell will last just a few days as warmer air comes behind, it likely will freeze over the Great Lakes and other bodies of water, meaning frigid temperatures will likely last the rest of winter, Maue said.

"It raises the chances for future cold," he said, adding it could include next month's Super Bowl in New York