February 15 10:15 AM Update- The cold will hold longer. That has been my suggestion for a few days, and now there is more support to how it. One of the results has been the National Weather Service expanding the Winter Storm Warning even farther north. Now Washington DC and Prince Georges County in Maryland is included through 4 AM Tuesday. Talbot and Caroline Counties on the Eastern Shore to Rehoboth DE until 7 AM. NWS has the potential for 4 to 6 inches (on target with my final call for snowfall) and 1/10 inch of ice on top tonight. The top end of my snow ranges likely for most and ice potential for the normally colder inland suburbs could reach up to 1/4 inch overnight. I have a new snow and ice timeline slider below to help you plan across the region.
One of the reasons for the cold to hold was the 7 AM plot of High Pressure in New England. That was the split point between the colder Canadian Model and the warmer GFS model. I have been leaning towards the Canadian since it performs best in arctic patterns. Plus, the recent deep freeze helped to ice up the northern Chesapeake Bay and freeze the ground. Even when warmer air aloft moves in at cloud level, it will take much longer for the surface to thaw.
I can’t suggest how schools will react Tuesday. Some places may be above freezing but have lingering ice or power problems as a result if icing. Still a wait and see set up.
Cold Air Damming:
This pattern is common in the winter, as a dense layer of very cold air holds close to the surface between the mountains and the Chesapeake Bay. Freezing rain and ice can last much longer than models suggest, even with a strong push of warmer air aloft. Below this split of the models showing the winning Canadian that I mentioned for this time frame, see how the High Resolution Rapid Refresh Model now supports my theory and holds the ice through midnight.
Simulated Radar: Snow/Ice Timeline (slider–>)
Notice the Cold Air Damming: As warmer air moves in, rain pushes through up the coast and into the mountains, but central Pennsylvania, and central Maryland hold the cold and ice in a wedge between the mountains and Bay and Coast.
Notes: Change To Ice
- South of Rt 50: Between Noon and 3 PM. Central and eastern Delmarva will turn to rain eventually.
- Washington/Baltimore I-95: Between 3PM and 6 PM. Ice lingers past midnight.
- Northern Maryland/Southern Pennsylvania: After 6 PM. Ice lingers into Tuesday morning.
Updated Snowcast
Most of my forecast is falling into line. The only adjustment I want to make is the higher end snow in southern Maryland that has already surpassed 6 inches. Also, the potential for the northern areas to maybe jump just above the 3″ mark. It might have been better suited to make the north zone 2″ to 4″ at the beginning.
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