There is confidence that there will be some snow tomorrow, possibly moderate, and that conditions will generally deteriorate as you head northeast. A Winter Weather Advisory has now been issued for tonight through tomorrow, for Southern Maryland, the Mid-Shore on the Delmarva, and Central Virginia. Areas further to the south and east are under a Winter Storm Warning. The National Weather Service, in a rare move, has also gone ahead and issued a Blizzard Warning for the Virginia Beach/Norfolk/Hampton Roads/Chesapeake Area.
Confidence is lower than usual, but finally starting to increase if only a little. The storm is forecast to rapidly develop just as it is approaching the Mid-Atlantic coast. Slight deviations in the rate of development and the storm track will likely have large implications for how much snow falls in the region. Shown below are two outputs from models I look at when making my forecast. On one hand, the European is far less aggressive with potential totals. A general 1-2" in Southern Maryland, with 2-4" on the Shore. On the other hand, the NAM Model is very aggressive with totals. That model has over a foot of snow on the Shore, a general 4-8" across Southern Maryland, and 1-3" in the DC Metro. Currently, I do not buy what the NAM is putting out. I believe the final solution is somewhere in between these two outputs, but I am swaying closer to the Euro. What I do like about the NAM is that it shows the sharp cutoff in totals that will exist.
Snow likely starts to fall tonight around Midnight. Conditions will likely deteriorate to their worst tomorrow morning, before sunrise-- especially east, as the storm intensifies. During this time, moderate bands of snow may begin pivoting around the storm's center off the coast from east to west, blown around by gusty winds and with falling temperatures.
Roads will become slick when the snow is falling. The snow tonight shouldn't be particularly heavy, so crews should be able to keep up with the snow on major roads. Although iciness on the roads is often a bigger threat at night than during the day. Airports may experience a few delays, especially if the storm comes further west, providing more snow. Widespread closures aren't anticipated in the D.C. area, but are possible at airports up the Northeast Corridor, especially tomorrow afternoon into the night, which would probably have significant impacts on flights scheduled to depart or land at National, Dulles and BWI.
What about area schools? With the core of the snow in the intimidate region falling in Calvert and St. Mary's Counties, I would say those districts have the best shot a closing (and that chance is high). In the very least, I would expect delays there. Anne Arundel, Charles, King George, and Prince Georges Counties have a modest shot at a delay. However, with the heavier snows falling well southeast of there, I would be cautious in hoping for closing. It is too early to make any predictions about schools for Friday. Check back tomorrow for that forecast (if it is needed).
As you can see, there is both the significant possibility of lower and higher snowfall totals than forecast. That is why it has been difficult to make this forecast. If the storm develops more slowly and further to the east, we may get very little snow. If it develops rapidly and further west, we may get hammered with more than 6". Satellite and radar tonight will serve as useful tools in monitoring how the storm is evolving. Stay with JB Weather on Facebook and Twitter for the latest updates on how the storm is involving, and the calls that area schools are making.
-John A. Bordash