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More cold, more snow, then winter starts

Do you remember what we were all doing a year ago on this date? Here's a hint: We were watching the weather forecasts as a weekend coastal storm threatened to dump heavy snow across the region on the night of Dec. 18-19.

Thank goodness that's behind us, right? Except that today, we're all watching the weather forecasts as a weekend coastal storm threatens to dump snow across the region on the night of Dec. 18-19.

In fairness, this one doesn't yet appear to be nearly as formidable as the 2009 blizzard. By this time last year, snow chances were set at 80 percent, and by the late afternoon, the predictions from Sterling were rising above 5 inches. By the next day, they were in the range of 1 to 2 FEET.

In the end, the Dec. 18-19, 2009 storm (photo, right) dropped an official (and debatable) 18 inches on BWI-Marshall Airport, now ranked the 9th deepest two-day storm on record for the city. Many locations saw far more than that.

The National Weather Service forecast for this weekend puts the snow risk at 50 percent, with the flakes beginning to fall sometime after 1 a.m. Sunday. Computer models continue to disagree on the precise track of the storm as it redevelops off the southeast coast of the U.S. A more westerly track up the coast would mean plenty of snow for our region. A more easterly track would keep the snow on Delmarva, and shift the greatest threat to New England.

NWS forecasters at Sterling this morning are saying the model solutions generally have been moving to the west. But at least one has shifted east. "Obviously the changeable nature in the forecast track of low pressure from the models provides a low-confidence forecast right now," they say, "and thus it's important to stay apprised of the latest forecasts for Saturday night/Sunday."

The Hazardous Weather Outlook says:

"A COASTAL STORM WILL BRING A CHANCE OF SNOW TO THE AREA SATURDAY
NIGHT AND SUNDAY. THERE REMAINS UNCERTAINTY REGARDING THE TRACK
OF THIS STORM. AT THIS TIME THIS LOOKS TO BE A COASTAL EVENT."

What seems more certain is that the cold weather that has settled into the mid-Atlantic states since the first of the month (graph, right) is going to hang around until further notice. Thursday's HIGH of 25 degrees at BWI was 2 degrees colder than the average LOW for the date.

Highs through the weekend will stick in the low- to mid-30s, with lows in the mid-20s. That's 10 degrees below the average for this time of year.

Blame a "blocking" pattern over Greenland that is holding a deep southward loop in the northern jet stream in place. And that has allowed arctic air to plunge deep into the eastern half of the nation, all the way to Florida's orange groves. 

The pattern is also what will bring this weekend storm out of the Southwest, slide it across the Southern states and out to the coast, where it promises to intensify and become a snowmaker for someone.

AccuWeather.com  (map, left) seems to be siding with a more easterly storm track, giving no more than a glancing snow-blow to the Lower Eastern Shore and nothing much at all for the I-95 corridor.

Foot's Forecast is taking an "either-or" approach:

"Scenario A would allow the system, now in the four corners area, to track close to the coast, bringing heavy snow for the entire I-95 corridor from Richmond, Va to Boston, MA. Scenario B would permit the system to track off the Southeast coast and further out to sea, with snow being confined to coastal portions of the Mid Atlantic."

"Timing for this system would be from late Saturday evening 12/18 into early Sunday evening 12/19 for the Mid Atlantic. One year to the day. Even the Climate Prediction Center came out guns blazing today with "Heavy snow and high winds remain a possibility for the Mid-Atlantic and Northeast." Just when you thought this weekend would be nice and calm."

Eric the Red is unequivocal: "Looks like the weekend storm is a no-go ... so that should do it."

Whatever happens, winter will arrive, officially, with the winter solstice, at 6:42 p.m. EST on Tuesday. Oh, and we may see more snow that day, as another clipper system passes by to our south, much like Thursday's storm. Stay tuned.

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