Storm with chance of winter weather to impact the DMV on Thursday

An inland track of the storm supports mostly rain, but a switch to snow at the end can’t be ruled out. 

Conditions appear ripe for a major storm system to swallow the Eastern Seaboard mid to late week, bringing heavy precipitation and gusty winds to the Mid-Atlantic.

Right now it’s looking more wet than white, but will herald the arrival of a frigid Siberian air mass that could deliver the coldest Christmas in years. 

The FOX 5 weather team is carefully tracking the impacts it could have on your holiday travel.

TIMING AND IMPACTS

The European model simulates heavy rain along the cold front Thursday

At present, it appears that Wednesday will feature pleasant weather, with highs in the mid 40s and mostly sunny skies. By Wednesday night, a few high, thin clouds will begin wafting overhead, foreshadowing our approaching storm system.

By Thursday morning, overcast skies will predominate, with a light southeasterly flow. Rain will arrive from southwest to northeast, probably sometime between sunrise and lunchtime. That rain, first along the warm front and then in the form of heavier downpours along a cold front. An isolated rumble of thunder can’t be ruled out in our southeastern areas, like the Tidewater and St. Mary’s or Calvert Counties. If you’re driving along Interstates 95, 66, 81 or 270, plan for a very wet ride. 

Sometime Thursday night or early Friday morning, models are hinting that a "dry slot" may work overhead. That’s a slice of cold, dry air wrapping on the back side of the storm. That would abruptly shut off precipitation for about twelve hours, give or take.

The European model depicts a changeover to mixed precipitation or snow in areas west of Interstate 95 on Friday. 

Then on Friday, we’ll probably see the "comma head," or a wraparound of moisture pinwheeling around the low pressure center. Amid an influx of chilly air out of the northwest, there’s a chance that second, lighter burst of precipitation could end as accumulating snow in the Potomac Highlands. A couple inches can’t be ruled out of the Panhandle of Maryland, the Blue Ridge and the Alleghenies. 

In Washington D.C. proper, expect perhaps some mixed precipitation likely ending as a dash of snow on Friday morning. There could also be a drop to subfreezing temperatures, which might make for treacherous travel as moisture left on the roadways turns to ice. 

WHY RAIN AND NOT SNOW?

Holistically, this system is looking like a rainmaker for the East Coast, rather than the snowstorm many were rooting for. Subsequently, the odds of a white Christmas are slim to none.

It all comes down to the structure and track of low pressure systems. Lows in the Northern Hemisphere spin counterclockwise. That means that winds to the right, or east, of the center tend to be warm and out of the south, with cold northerly or northwesterly winds west of the storm’s track.

For that reason, a winter storm setup in the D.C. area would require either an offshore low or a low skirting to our south. That won’t be the case. 

Instead, the low pressure system will likely ride right up the Appalachians, relegating any snow chances to parts of the Midwest or Upstate New York.

ATMOSPHERIC SETUP

An ensemble model, or model depicting a range of possibilities, hints at a mostly inland track. 

The overarching atmospheric setup begins over the Bering Strait between Russia and Alaska, where a dome of high pressure is parked. That high brings sinking air, clear skies and mild temperatures, while simultaneously defecting the jet stream to the north.

Downstream, or east, of that high, the jet stream then dives back southward — allowing a pocket of high altitude cold air, low pressure and spin to ooze south over the central and eastern Lower 48. Our surface low will develop on the eastern periphery of that upper-air disturbance.

A model simulation of temperature anomalies leading up to Christmas, marking bitter cold air invading the Plains. We get a taste of that chill here. 

Meanwhile, Arctic high pressure at the surface, characterized by bitter-cold, dense air hugging the ground, will slide out of British Columbia, Alberta and Saskatchewan and crash south over the Plains. That will bring widespread subzero readings to the northern Plains and Upper Midwest, with overnight lows down near minus-20. It’s possible that Christmas weekend could even feature temperatures in the upper 20s to near freezing all the way to the Gulf of Mexico coastline. 

Some of that cold will bleed east into our region around Christmastime, with forecast highs only in the lower 30s. That said, it could be even colder. There’s a slight chance it could be the coldest since 2000, when the high was only 28 degrees. 

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