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