Extremely cold air in blue and purple reaches Southwest Virginia on Friday morning, as shown on this National Weather Service forecast map. Courtesy of NOAA.
Extremely cold air in blue and purple reaches Southwest Virginia on Friday morning, as shown on this National Weather Service forecast map. Courtesy of NOAA.

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They call this a “blue norther” out in the Plains states. It will be more of a “blue wester” for us.

Make no mistake, though, the air arriving in Virginia on Friday morning originates from near the North Pole, preceding Santa Claus by a day as it sets up the coldest Christmas Eve and Christmas in Southwest and Southside Virginia since the 1980s.

An Arctic cold front will touch the southwest tip of the state not long after midnight on Friday morning and blast eastward, reaching the Blue Ridge by about 4 a.m. and moving east of Southside toward Richmond by shortly after sunrise.

When it goes by, winds will switch to the west and blow in bitter chill with big gusts, likely over 40 mph at times most everywhere, perhaps 50-60 mph in and near the mountains. That will be enough for some tree limbs to break and for some sporadic to scattered power outages.

Temperatures are expected to slowly rise on this Thursday evening, but will do an about-face immediately upon the front’s passage. An initial drop of 10 to 15 degrees is possible in the first hour, followed by a steady but persistent drop through the day, with most of our region already in the single-digits to teens, west to east, by sunset Friday.

That plunge won’t compare to Cheyenne, Wyoming, where the temperature dropped from 42 degrees to 2 degrees in a single hour as the same Arctic front passed on Wednesday, on the way to a low of -25 Thursday. But for an air mass that has crossed a continent and is running over a speed bump in the Appalachians, that’s a significant polar plunge that really hasn’t happened in our region in a similar fashion since February 2015.

The cold front will likely be accompanied by a band of showery precipitation, perhaps rain immediately ahead of the front, but quickly turning to snow as the front goes by. A brief bout of sideways, wind-blown snow may occur, with some whiteness on the ground west of I-77 and perhaps in a streaky fashion as far east as the Blue Ridge.

Downslope flow off the mountains after that will tend to dry up the precipitation band, but some flakes may blow through even into Southside.

One concern is that moisture from the frontal rain/snow showers will collect on roads and then quickly freeze into ice on road surfaces, sometimes called a “flash freeze.”

Mercifully, we have several hours between Thursday’s ample rainfall (ice in higher elevations near the mountains) and the arrival of the Arctic air, allowing draining and drying on streets, or the “flash freeze” issue could be a real skating rink. Still, anywhere water has puddled on roads will become solid ice quickly on Friday, so beware even if most of the roads look dry where you are.

Some higher elevations in Southwest Virginia experienced icing from persistent rainfall and barely freezing temperatures on Thursday. This limb developed some icing at 1,600 feet elevation a few miles south of Roanoke, with no icing only 100 feet lower. Photo by Kevin Myatt.

Low temperatures by Christmas Eve are expected to be near or slightly below zero in much of the region west of I-81, with single-digits to near 10 over most of the region from I-81 east to Southside.  It now appears Saturday will be the colder of the two Christmas weekend days, with temperatures on Christmas morning perhaps 5 or so degrees milder.

Christmas Eve and Christmas Day will each easily be the coldest Dec. 24 and 25 we have experienced in our region since either 1983 or 1989, depending on exactly how cold it gets and some regional variation in temperatures on those days during those years.

It will also be the coldest weather our region has experienced at any time of winter since some single-digit and below-zero lows in early January 2018.

The Arctic plunge is hitting us because of a monthlong-developing atmospheric setup involving strong high pressure near the North Pole pressing deeply chilled air away from the pole, and high pressure over the western U.S. pile-driving it into the central and eastern U.S.

A “bomb cyclone” low-pressure system deepening rapidly over the Great Lakes is giving this Arctic blast extra propulsion across the eastern half of the U.S. (If the jet stream trough bringing the Arctic air had arrived faster, the coastal low-pressure system bringing us our rain and freezing rain on this Thursday might have been the “bomb cyclone” and we would have had a pre-Christmas snowstorm.)

A third leg of a potential prolonged cold pattern, high pressure over Greenland that could lock in cold air over the eastern U.S., has broken down in the past couple of weeks.

So this big chill won’t last long. Temperatures modify back to normal 40s highs, 20s lows much of next week, and might make a push toward 60 by New Year’s Day.

Journalist Kevin Myatt has been writing about weather for 19 years. His weekly column is sponsored by Oakey’s, a family-run, locally-owned funeral home with locations throughout the Roanoke Valley.

Kevin Myatt

Kevin Myatt wrote the Weather Journal in The Roanoke Times for 19 years. He has led students on storm chases and written for “Capital Weather Gang.” Twitter: @KevinMyattWx. Email: weather@cardinalnews.org.