* Winter weather advisory for most of area late tonight through 11 a.m. Thursday *
The ocean storm or “bomb cyclone” exploding off the East Coast will pass far enough offshore for the Washington region to miss the storm’s brunt. However, because it is predicted to scrape the region with a period of snow during Thursday morning’s commute, it could cause disruptions.
Generally, a dusting to two inches of snow should fall in the metro region, with potentially two to four inches in our east and southeast areas near the Chesapeake Bay. Amounts should drop sharply west of Fairfax and Montgomery counties, where some areas may not see any snow or just flurries.
Because air and ground temperatures are both well below freezing, snow will stick to all untreated surfaces, causing slipperiness. Some schools, especially east of the city, could delay or close Thursday (SchoolCast to be posted by 6 p.m. Wednesday).
“If this threat does materialize during the Thursday morning rush-hour, many roads could quickly turn icy,” the National Weather Service cautioned. “This could lead to dangerous traveling conditions, multiple accidents, and extensive delays.”
Light snow may develop between 11 p.m. and 3 a.m. Wednesday night into Thursday morning from southeast to northwest, and it should end around 10 a.m. along Interstate 95 and early afternoon near the bay. The period of steadiest snowfall is probably between 4 and 7 a.m., potentially coinciding with the early part of the morning commute.
Note that this is particularly tricky forecast because the Washington area is on the western periphery of the expected snowfall. If the storm shifts closer to the coast, amounts could increase by an inch or two. But if it wobbles farther east over the ocean, we’d see very little — if any — snow.
East of I-95, this event rates as a Level 2 “disruptive” on our Winter Storm Impact Scale. While amounts are expected to be light, snow falling on cold roads during a commuting period elevates this above a “nuisance” event. Very cold temperatures both before and in the storm’s wake also contribute to the impact.
Near and west of I-95 through the metro region, in the zone where a dusting to two inches is most likely, this rates of as a Level 1 “nuisance” event because the snow will be light and easy to sweep away, despite the potential for some slick spots and perhaps some school delays.
In the zone well west of Washington where we expect just flurries, this event is not rated.
Following this storm, extremely cold air will surge southward — the most frigid of the season so far. Wind chills Friday morning will drop below zero throughout the area.
The forecast remains tricky for several reasons.
1. This is an unusually strong storm that is forecast to track northward along a front over the Southeast coast before turning more toward the east. Exactly where it makes that turn could affect our area, especially counties south and east of the city.
2. The air over our region is extremely dry, and there will be a period when snow is falling but evaporating before it reaches the ground. In the past, we’ve occasionally gotten burned by the dry air eroding the western edge of the snow, greatly reducing amounts.
3. The gradient between no snow and where several inches of snow accumulates is likely to be fairly sharp.
4. Bands of heavy snow could set up somewhere southeast and/or east of the city to locally enhance amounts. The most likely locations for such intensified snowfall would be over St. Mary’s County, the Northern Neck of Virginia and the Delmarva Peninsula. These areas could see snowfall rates of an inch per hour for a brief time early Thursday morning.
5. The fluff factor. The cold temperatures will help the snow take on a more powdery consistency, piling up a bit more quickly than usual. This could increase amounts over what we’d normally expect from the amount of moisture headed our way.
Why won’t we see more snow from this storm? Capital Weather Gang contributor Jordan Tessler posted two nice maps which shows storm tracks from Washington’s biggest snowstorms (on the left) vs. the predicted track for Thursday’s storm — which is well to the east (on the right).
I made this map of estimated low tracks of DC's biggest storms (does not have Blizz of 16). Now compare to the WPC track map for this one, and you'll see (partially) why we're only getting grazed, and the coast going to take the hit pic.twitter.com/OsgEq9PDRs
— TerpWeather (@TerpWeather) January 3, 2018
There is quite a difference.