Get ready for the coldest Christmas in 20 years, and that's the good news

The coldest Christmas Day in more than 20 years is on tap for Monday in the metro area, and temperatures will only nose dive from there to well below zero by next week, the National Weather Service said.

Monday's predicted high of 4 degrees above zero will make the holiday the coldest since 1996 when thermometers registered a high of 9 below.

Arctic air that has been bottled up across Siberia and the North Pole will break off "from where it belongs" and rush south into Minnesota on Sunday, and with it bring the first readings with negative numbers in the Twin Cities this season, said Eric Ahasic, a meteorologist with the National Weather Service in Chanhassen.

"We've been watching for this cold air to come in for a while, and on Sunday you'll start to feel it," Ahasic said.

Once the cold arrives, it won't give up its grip anytime soon. Temperatures during the day will be stuck in the single digits and definitely will fall into the single digits below zero right through New Year's Day, and possibly longer.

And there is the possibility the mercury could go even lower, Ahasic said.

"It certainly looks to stay well below normal into the New Year," he said. But to drop to minus 22 degrees as it did on Christmas morning 1996, "we would need some snowpack to get that cold."

As the Winter Solstice arrived Thursday morning — that means the sun will start moving northward — the Twin Cities had just 2 inches of snow on the ground. That's enough to qualify for a White Christmas, said Pete Boulay of the Minnesota State Climatology Office.

Cold snaps are not unusual on Christmas Day, but over the past two decades it has been rather mild on the holiday. Only two times has the low temperature in the Twin Cities dropped below zero on Christmas: 6 below in 2008 (with a high of 26 degrees) and 17 below (with a high of 12 degrees) in 2000.

Last year a thunderstorm dropped nearly an inch of rain accompanied by a high of 37.

The bitter cold on Christmas Day 1996 was a harbinger of some of the coldest air ever seen in Minnesota. In that year, the lowest temperature ever recorded in the North Star State occurred on Feb. 2, when the thermometer registered 60 below in Tower in St. Louis County north of Duluth. That year also saw below zero temperatures for 14 straight days in the Twin Cities, including 32 degrees below on Feb. 2. The Super Bowl will be played here Feb. 4.

Ahasic said forecast models are not as accurate after five to seven days, so he's not ruling out a prolonged period in the deep freeze like 1996. But without more snowfall, he doesn't see readings plummeting quite that low.

Tim Harlow • 612-673-7768