This afternoon the National Weather Service issued a winter storm watch for Thursday afternoon through early Friday morning along the southern New Jersey coast from Ocean County on south to Cape May County. The watch also includes parts of Delaware back through northeastern Virginia. The watch states that 2 to 6 inches of snow is possible.
Okay, let me be blunt here. There is just as much chance at this point for a complete miss or a major winter storm for much of coastal New Jersey and even the New York City and Philadelphia metropolitan areas. The key question in this forecast is whether the disturbance over the southern Plains will interact or even phase with a strong Polar disturbance currently over northern North Dakota.
The latest model guidance does show a better potential for a phase of these two disturbance on the NAM and GFS guidance. However, the CMC, ECMWF, and UKMET guidance all keep the two disturbances separate. There is no doubt that we are dealing with an amplified Sub Tropical disturbance that is pulling moisture northward. The issue at hand that is prevent the potential for a major winter storm is the timing of the Polar and Sub Tropical disturbance is such that leads to suppression of the moisture over the southern Mid Atlantic.
Now the key with the Sub Tropical disturbance here is that this intensifying Sub Tropical disturbance is also pumping up the Southeast ridge over Florida and the Bahamas. We can see this with the red colors thus sinking air. This factor I think the non-NCEP models are under playing that would suggest a better potential for phasing thus a better chance for snowfall for everyone. Of course, the worst thing that can happen is to have too early of a phase and draw warm air in, changing the precipitation to rain.
The draw back in this set up is that the low level cold air is having some difficulty in making headway to the coast and I'm concerned about boundary layer conditions leading to more snow melting on the surfaces rather than sticking. Further, the speed of this low, suppressed or not, is going to be rather progressive which will likely lead to less precipitation output than what the current guidance is showing.
Considering these factors, I understand why the NWS issued the watch. Better to be safe than sorry. The case can certainly be made that there is potential here. Potential to over perform not only along the New Jersey coast but all of the Philadelphia and New York City metropolitan areas. At the same time, given what I'm seeing on the water vapor satellite picture and overall guidance I like the idea of going 2 to 4 inches along the New Jersey coast, a trace to two inches over southwestern and west central New Jersey up through northeastern New Jersey and Long Island, and nothing but snow showers (if that) elsewhere.
I'll be keeping an eye on this upper level disturbance and potential interactions through the next 24 hours and will update on the latest details when available.