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Tuesday, March 19, 2013
The atmosphere is sometimes poetic in its timing of extremes.
A year ago, March was Roanoke’s hottest on record. Every day starting on March 11 had a high temperature of at least 60. Highs hit the 70s on 15 of those 21 days, and the 80s on six of them. A year ago today, the high was 81 degrees.
Fast-forward a year, and we are entering what will likely be one of our coldest starts to astronomical spring we’ve seen in many years.
Strong high pressure systems near Greenland and the North Pole are not allowing the jet stream to move air masses through on their typical seasonal pace. As a result, cold air is becoming trapped behind the blockages, and forced south into the central and eastern U.S.
A year ago, low temperatures were in the 50s from March 20 to 25, barely below the normal highs. Today is by far the best chance to barely reach 50 for a high temperature in that same time frame this year.
March is already about 3 degrees below normal in its first 19 days. Saturday’s sunny 77 — perfectly timed for St. Patrick’s Day events — was very much the exception.
Perhaps of even more interest than low temperatures hanging on until the end of March is the potential for snow.
The same blocking pattern of high pressure over the far northern latitudes is also forcing storm systems in the jet stream to dive farther southward.
Over the weekend, it is possible one of these storm systems will scoop up some Gulf of Mexico moisture and fling it into the unseasonably cold air over us. Some forecast models even wrap this up into a full-fledged coastal storm hugging the Eastern Seaboard.
There’s a lot that can go wrong with potential snow setups in midwinter — and even more in early spring.
But the pattern of blocking high pressure to the north defies the season enough to make it possible that the cold air will be deep enough to support snow, even at our latitude this late in the year.
The cold pattern may even hang on long enough for there to be more than one chance at significant snow in late March or even early April.
A winter reluctant to get started is now reluctant to leave.
Weather Journal appears on Wednesdays.
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