Temperature tonight take a nosedive as an impressive Canadian high pressure system traverses the Cumberland Plateau and the Appalachian Mountains. Mainly clear skies and slackening winds (and some leftover snowcover) will aid in quickly cooling down the atmosphere. Lows tomorrow morning will bottom-out in the mid to upper teens in northern MD, and near 20-23 degrees closer to the metro region.
Both Tuesday and Wednesday will offer biting cold temperatures in the lower 30s as the effects from the said Canadian high ooze into the Mid Atlantic.
More Tricky DC forecasts:
As is often the case in the Nation's Capital, the difference between a "good forecast" and a bad one can come down to a matter of miles. Due to our location near the Atlantic Ocean, and Mid-Latitudes, the rain/snow and snow/ice lines often sit right on top of the District--and turns generally easy forecasting into a ghoulish nightmare.
During the afternoon Wednesday, a low pressure system will begin organizing along the Canada/United States boarder in the upper Midwest, while a cold front develops, slicing through the center of the US. By Wednesday evening, another separate low pressure area should develop along the frontal boundary around the Gulf Coast.
At the same time, the aforementioned Canadian High Pressure cell will make itself comfortable in central Quebec. This type of set-up is nearly a classic CAD (Cold Air Damming) example-->High pressure to the north funnels cold surface air southward along the lee side of the Appalchians, and often causes some of the worst ice storms for the DC metro region.
Now, if this were a classic CAD set-up, we'd basically have no worries with this forecast. But this High pressure cell is situated so far north (usually, we like to see the high over upstate NY), the cold surface air is not as pronounced, and will have a tough time keeping precip in the "wintry" form.
DCweather Snowstorm Outlook
When: December 15th-16th
Impact:
Confidence: Low/Med
Commentary: Precip will likely overspread the region late Thursday AM as a rain/snow mixture. Most of this should change over to rain by midday as warmer surface temperatures move in. By Nightfall, however, an ice/sleet mixture may be in the works for the region as temperatures in the mid levels of the atmosphere warm above freezing. There is below normal confidence with the forecast due to the shallowness of the cold air along the eastern slopes of the Mountains. At this point, I don't see this system causing significant problems around the region--but for those of you who have lived here for awhile know 1/2 inch of snow can cause major problems around here.
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