*A Winter Storm Watch is in effect for portions of northern and western Maryland as of 2 PM EST*
Low pressure moving northeast from the Tennessee Valley will transfer energy to a new area of low pressure off the Atlantic coastline that will move northeast. As the moisture from the first area of low pressure overspreads the Middle Atlantic states, precipitation will fall into cold, dry air at the surface and will produce widespread snow and sleet north and west of Annapolis. As a warm front moves north through the region during the afternoon, the frozen precipitation will change to rain. A secondary low off the Atlantic coast will produce heavy snows across New England into Sunday. Here are the top five questions about what we can expect from this system through Saturday evening:
Will the cities see any snow from this system?
With dry, relatively cold air in place over the Middle Atlantic states, the precipitation will initially fall in the form of sleet and snow around Baltimore and Washington before changing over to rain. Annapolis may see a shorter period of sleet and snow before the changeover, and areas to the south and east of Annapolis will see primarily rain from this system. Accumulations will be one inch or less around Baltimore with a coating or less in Annapolis, but heavier accumulations will only be about 20 miles to the north and west. Westminster and Frederick may pick up anywhere from 3 to 6 inches before changing to sleet and freezing rain. To the south and east of Annapolis, a cold rain is expected from Richmond VA to Salisbury MD to Dover DE.
When will this system impact central Maryland?
The current thinking is that precipitation will begin during the late morning or early afternoon hours and continue into the evening hours. In Baltimore, Washington (and especially Annapolis), the snow and sleet may only last from one to three hours before the changeover to rain. Rain will then continue for several hours into the evening. With temperatures rising into the mid and upper 30s, ice will not be a problem in these areas.
What factors might necessitate a change in the forecast?
Predicting the rain/snow line, and the changeover time, is one of the most difficult tasks in meteorology. This is particularly true in the costal plain around Baltimore and Annapolis where our weather is impacted by the Chesapeake Bay and the Atlantic Ocean as well. As mentioned above, heavier accumulating snow will be within a half hour drive of Annapolis. Should the cold air damming effect hold in place a bit longer, the changeover to rain will be delayed; however, even in this scenario I do not see Annapolis receiving more than one inch of snow. Conversely, Annapolis may not see a flake of snow if warmer air erodes the cold air at the surface sooner than expected.
What will driving conditions be like at 3 p.m.?
Roadways will be wet. There is no threat of freezing on the roads south and east of Baltimore. Snow-covered roads will be more of a problem heading north toward Towson, north along Interstate 83, and along route 70 toward Frederick.
When is the next potential winter weather event?
There are no winter weather events expected for at least another week. Sunny, seasonably cool conditions can be expected from Sunday through Thursday of next week. However, the long-range outlook does indicate the potential for significantly colder and stormier conditions after December 20.