“The most unusually cold air in the Northern Hemisphere is set to nose-dive into the U.S. to start March,” tweeted Ben Noll, an atmospheric scientist based overseas.

What that means on the ground is that large portions of the north-central U.S. could struggle to get above zero, with widespread nighttime lows in the minus-10 to minus-20 range a decent bet in that region. It’s also possible that every state except perhaps Georgia, South Carolina and Florida will face high temperatures at or below freezing during the stretch.

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This morning, DTN Weather, a provider of data and forecasts, highlighted the widespread nature of the massive cold snap slated to enter the Lower 48 as March gets going.

“Temperatures will run 20-30 degrees below normal in spots,” it wrote.

Some locations seem likely to end up even colder than 30 degrees below normal. While the forecast highlighted above is still at a range where confidence in details remains on the low side, it is also very impressive for a five-day average, one that will smooth some of the extremes seen during shorter time scales.

Around March 4 or 5, there could be a day or two with temperatures 20 to 40 degrees below normal encompassing about one-third of the country, from Montana to Wisconsin in the north and then sweeping south across most of the central United States between the Rockies and Mississippi River. The cold ultimately makes it to the Mexico border with Texas and into the Gulf of Mexico.

In addition to the cold being extreme for such a late date in winter, it is also expected to affect an unusually large part of the contiguous United States. Brian Brettschneider, a climatologist from Alaska, points out the 90 percent odds of below-normal temperatures over one of the greatest portions of the country since such forecasts began in 2014.

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Some places are waiting for the big cold to arrive. Others continue to live it.

Even before the advertised Arctic outbreak to come, much of the north-central portion of the country is already dealing with an extra deep kind of freeze. In Montana, for instance, wind chills below zero are anticipated for much of Tuesday.

Actual temperatures were near or below zero for lows in the Dakotas, Montana, Minnesota and Wisconsin on Tuesday morning. Single digits stretched well south into portions of Oklahoma and Texas.

Although the Arctic onslaught in early March is set to affect much of the Lower 48, the worst of its cold seems likely to fit into a similar pattern seen of late.

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The general story of the past several weeks has been of major to extreme cold being centered on the northern Plains region and easing slightly heading west and east. The difference from normal temperature maps so far in February shows that idea well. A huge chunk of real estate is 20 degrees or more below normal, which is exceptional on a monthly time scale.

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A place like Great Falls in Montana, just to the east of the continental divide, is running a whopping 27 degrees below normal for the month of February.

Great Falls broke another record low Tuesday morning, with a reading of at least minus-22. The average temperature there is about minus-1 this month to date. That’s the second coldest February on record for the city, and the coldest since 1936, when observations were taken at a different location nearby. Third place there is an incredible 10 degrees warmer!

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Although Great Falls might not get its coldest February ever recorded, it is still a remarkable chill compared to recent history. A number of other locations nearby, like Rapid City in South Dakota, are testing similar marks. The upcoming cold spell should again target these areas with some of the harshest conditions.