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According to NOAA's GODAS system the heat content of the top 300 meters (about a thousand feet) of the North Atlantic ocean off the east coast from Cape Hatteras the Prince Edward Island is way above normal. The average temperature of the water column from the surface to 300 meters deep is greater than 2 °C above normal.
Click on image for movie.
The deep pool of unusually warm water is the source of large amounts of additional water vapor to storms. Warming water 5 degrees Fahrenheit above normal, as this figure shows, increases the amount of precipitation greatly because evaporation rates rise very rapidly with increasing water temperature. That leads us to the forecast for Wednesday.

Bullseye on DC.
The NAM model, which has a tendency to over-predict rain and snow, has just produced a worst case forecast for the mid-Atlantic - over 2 inches as water of total precipitation across a wide area. If this would all be snow, it could be 2 feet or more.

The ECMWF model shows a potential for intense snow north and west of Washington, DC.

snowquester forecast
Blue colors are below freezing, green and yellow are above freezing at about 5000ft. (850mb). The blue/green line is frequently close to the rain/snow line in east coast winter storms.

Air warmed and moistened by the warm pool of water and the Gulf Stream, will rise up over the cold air near the surface. It's a process called isentropic lift. Air tends to flow along a surface where it doesn't gain or lose heat to the environment. That means a relatively warm air parcel cools (adiabatically) and forms clouds as it is blown by storm winds over cold air at the surface. This is one way that east coast storms can generate large amounts of snow. Because the warm pool is very deep it can warm and moisten air for days.

The temperature contrast between the Gulf Stream and polar air that moves south from Canada provides extra energy and moisture to east coast storms. When the warm waters are closer and warmer than normal and dynamical factors come together, very heavy snows are possible on the east coast.
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