Much colder second half of January on tap with weakening polar vortex

Much colder second half of January on tap with weakening polar vortex

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Much colder weather is on tap for the second half of January with a weakening polar vortex, according to forecasters.

But don’t look for anything like the horrific, record cold that punished Wisconsin and the Upper Midwest last winter, AccuWeather said.

After a big storm system Friday and Saturday moves out, the National Weather Forecasts highs just near 14, 17 and 20 Sunday through Tuesday and lows around 4 and 2 Sunday night and Monday night, while 27 Storm meteorologist Max Tsaparis predicts highs near 14, 14 and 18 and lows around 0 and 10.

And that won’t be the end of the cold, according to AccuWeather.

"We expect conditions to turn much colder during the last two weeks of January," AccuWeather Lead Long-Range Meteorologist Paul Pastelok said. "There will be some weakening and stretching of the polar vortex, which will allow cold air to drain southward from Canada in stages during the second half of the month. However, a big breakdown and major shift of the polar vortex, which would allow an extremely cold discharge, is not anticipated.”

The polar vortex keeps cold air locked up near the Arctic Circle when it's strong, and that has been the case this winter. When the polar vortex weakens and shifts its position, cold air can escape south. That was the case in last winter’s bitter cold snap.

In addition, a large southward bulge in the jet stream is expected next week that is likely to persist and stick around for two to perhaps four weeks. That will enable cold arctic air to move down into the U.S., following a mild first half of meteorological winter.

"By next weekend, nearly all of the lower 48 states may be colder than average," Pastelok said. "Temperature departures from average will probably be more like 3 to 10 degrees below average.”

Normal highs for the second half of January, which is the coldest part of the year, are at 26 and 27 and lows 11 and 12 for Madison, according to the Weather Service.

The colder trend is expected to continue into February, and AccuWeather's long-range team of meteorologists is predicting February to average 1 to 3 degrees below normal for much of the eastern half of the nation, with the exception of Florida.

"As we get into February, the polar vortex may strengthen and retreat toward the Arctic Circle once again and the jet stream dip may set up more toward the middle of the nation, which would suggest cold conditions there but result in moderating cold in the East," Pastelok said.

Deep freeze: Read our coverage of the early 2019 polar vortex in southern Wisconsin

Deep freeze: Read our coverage of the early 2019 polar vortex in southern Wisconsin

Winter weather has been pounding southern Wisconsin, bringing lots of snow and then extreme cold temperatures. Keep up with the latest news here.

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