Winter Weather Advisory issued for D.C. area as first snowfall of season hits

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What a difference a day makes! While the chance for snow has been in the forecast for most of the week, the chance for measurable snow was originally confined to Southern Maryland and the Eastern Shore. However, weather models over the past 24 hours have trended both stronger with the storm system and closer to the eastern seaboard.

The result? Snowfall is now expected to encompass the I-95 corridor during the overnight hours. Last winter, the first inch of snow did not threaten Washington, D.C. until January 30. But with the increasing likelihood of more than an inch of snow in Washington tomorrow, the National Weather Service issued its first Winter Weather Advisory of the year, which will go into effect at midnight tonight and remain in place until 4 p.m. on Saturday.

What You Need To Know
As of Friday morning, snow is not expected to move into metro D.C. and areas north and west during the overnight hours, likely beginning in the hours before dawn. The exception to this is Southern Maryland, eastern portions of the Northern Neck of Virginia, and southern parts of the Eastern Shore could all see rain mixing with snow as early as the evening commute hours tonight.

Unlike typical coastal storm systems that bring considerable snow to our region, the area of low pressure is located farther east (offshore) than usual. This means the risk for the heaviest snowfall and highest accumulations is actually east of I-95, as opposed to the north and west we are more used to.

While there is ample cold air above the surface to support snow, temperatures at ground level are very marginal with this event with models suggesting many across the region may remain just above the freezing point of 32 degrees. This means that some melting will occur when the snow hits the ground, especially on the roadways.

Our forecast currently calls for 2-4 inches of snow in the immediate Washington, D.C. area and those totals are mostly on the grass. With temperatures slightly above freezing, pretreated roadways in the region likely more wet with maybe a slushy coating as opposed to snow covered. Snow wraps up in the area Saturday afternoon.

What Could Go Wrong
Storms like this make me very nervous. We know there will be a sharp cutoff in snow as you head north and west of town. The question is where will that snow cutoff be.

Many models have the snow totals cutting off around Frederick, Md. area. There are a few, like the American model, that are pulling that snow cutoff line much farther west, and if that is the case then we will need to pull our 2-4 inches contour farther to the west, possibly to the I-81 corridor. This could also bring some heavier snowfall into the downtown D.C. region, possibly up to 3-5 inches of snow with even a few pockets of 4+ inches possibly locally.

The "jackpot totals" for this system are expected to be east of I-95. The Eastern Shore, Southern Maryland are some of the areas that could do the best with this snow, with the upper end of guidance showing the potential for half a foot of snow in some areas east of town.

Of course there is always concerns in the other direction. We could be underestimating the amount of melting that will occur as the snow falls, particularly if this ends up being a lighter snow event. Since the storm has not developed yet, if it ends up being weaker or develops a little farther east than weather models are suggesting, we could end up with snow totals being on the lower end of things.

As of this writing, both Tucker Barnes and I feel that the potential on this one at this time if for snow totals to surprise on the higher side of things around the I-95 corridor.

One thing that is certain: this forecast will need to be adjusted later this afternoon as new weather models roll in. Caitlin Roth with bring you updates this evening, and Gary McGrady will be covering the snow tomorrow. Stay tuned!