There are several factors favorable of big snow and several factors unfavorable for big snow. Low pressure is set to begin bombogenesis along the NC coast in the right spot for big snow here, but that’s if it’s December, January or February. Monday night will be mid-march. But, the air mass is unusually cold for this time of year as a lobe of the misnamed “polar vortex” passes by to our north in Canada. This and the fact that models continue to portray the heaviest bands at night favor snow at the onset, as day time frozen precipitation is hard to come by due to the March sun. Another issue is that the models do not fully phase the storm as the precip from the bombogenesis is impacting us. A secondary low, albeit weak, will still be spinning to our west and that is not an ideal setup for big snow, especially this time of year.

As with any strengthening or bombing low, the position of the coastal front at both the surface and mid-levels is critical for the rain/snow line or mixing line. The 12z GFS has the surface stay below freezing, but freezing rain fall for a period of time during the storm due to warmer air injecting itself up above. Meanwhile, the euro is a little farther east with the low, and thus the coastal front, with the heaviest snow right up to DC to Baltimore with lighter accumulations west. Even if the warmer tongue of air stays east, I fear sections adjacent to the bay will go above freezing due to water temperature of the bay being in the upper 40s to 50 degrees. An easterly fetch of wind in both the surface and mid levels at the beginning of the storm may cause issues with precipitation type near the bay because of the temperature of the bay itself.

My preliminary forecast is as follows:

Directly along I95 from DC to Baltimore: 4-8 inches with the lighter amounts the further south/east one lives
North and west of I95 from Owings Mills to Rockville to Centreville: 8-12 inches
Northeastern MD (Harford and Cecil counties): 9-13 inches
Southern Anne Arundel county, southern and eastern PG county, western Charles County: 2-4 inches (this can also be true of eastern sections of Baltimore and Baltimore counties along the Bay)
Eastern Charles, Calvert, and St. Mary’s counties: 0-2 inches

Timing is Monday night into Tuesday morning. My final forecast will come out Sunday night.

12z GFS:

12z NAM:

12z Canadian:

12z Euro ensembles:

Local National Weather Service forecast as of time of post (4:00pm 3/11):

The mid-day model runs diverged fairly significantly with the snow possibility for Monday night into Tuesday. First up was the GFS, which had a coastal hugger and inland track once it got up to northern New England. The hugging of the coast resulted in the rain/mix line going over top of the I95 corridor for the Mid-Atlantic in the middle/end of the storm resulting in what would likely be a 6 or 8 inch slop when it was all said and done. The Canadian came in next and its 12z run took the storm east with virtually no snow for the I95 corridor in the Mid-Atlantic. The euro then came in splitting the difference and giving all snow to the I95 corridor and southern MD with accumulations likely over a foot.

Out of the three, I find the GFS and euro scenarios to be the most likely with the Canadian being the more unlikely of the three. In fact, the Canadian’s upper level energy was weaker than the other two and its model run formed a rather odd looking double barrel of low pressure oriented north-south out over the Atlantic. It was odd given the scenario and the surface low pressures splitting like this and weaker upper level energy may have been a result of the model initializing poorly. The 18z GFS was nearly identical to the 12z run, but it made a small step towards the euro’s solution in the upper levels of its model run.

Perhaps the best sign for snow lovers is the euro ensembles that came in the middle of the afternoon. The ensembles gave Baltimore a 50% chance of a foot of snow or more. This is a quite high probability this far out and would be a huge fail for the euro model suite if no snow were to fall for Baltimore.

My decision on whether I think snow is a probability or not will come Saturday afternoon.