Low pressure will be pushing off the Southeast US coastline in a northeastward direction early Sunday morning while at the same time a vigorous upper-level wave of energy will be dropping southeastward across the upper Great Lakes. The strength, movement and timing of this “northern branch” wave of energy is critical to the ultimate track and strength of surface low pressure off the Mid-Atlantic coastline late Sunday and Sunday night. As it stands right now, it appears that even though the “northern branch” wave can generate snow showers and steady light snow in the Mid-Atlantic region late Sunday, more substantial precipitation is likely to stay off the coast – however, it is a close call and still bears watching.
Upper-level energy and European model trend
The tendency in recent runs of the European computer forecast model is to “dig” the northern branch energy a bit more to the south as it crosses the Great Lakes and for more of a “negatively-tilted” trof axis. The forecast maps at 500 millibars (above) show the orientation differences of the “northern branch” wave of energy between last night’s 00Z model run (left) and today’s 12Z model run (right). The black line indicates the orientation of the trof axis associated with the upper-level wave on Sunday night and it changes from a positive tilt (i.e., from NE-to-SW) on last night's run to a slightly negative-tilt (i.e., NW-to-SE) on today's run. If this trend continues over the next couple of days that could allow the surface low pressure system to hug the coast more than is currently projected and there is some reason to believe this could indeed take place based on biases of the European forecast model and the recent trend itself. (By the way, NOAA's GFS model also trended a bit to more of a "hug" the coast scenario with the low pressure system). If these trends were to continue then there could be more substantial snow in at least parts of the Northeast US come late Sunday night – stay tuned.
Meteorologist Paul Dorian