Mount Holly has KEY messages in their AFD lol. Number 3 below-
KEY MESSAGE 3...A strong frontal passage is expected later Wednesday with the potential of a coastal storm for Thursday and Friday as a secondary low develops off the coast. Impacts are very uncertain at this time depending how close the low tracks to the coast. By the middle of the week, an amplified upper level weather pattern is expected to develop of the eastern third of the United States. A strengthening and deepening upper level trough will be located over the Great Lakes on Wednesday, stretching all the way down toward the Gulf Coast by Wednesday night. At the surface, it is fairly confident, that a primary area of low pressure will be tracking across Ontario and Quebec with cold front trailing back across the Appalachians. This at the very least will lead to some shower activity across the area on Wednesday. Temperatures look to be several degrees above average, where highs will likely top out in the upper 40s to low 50s.
Beyond Wednesday though, the pattern becomes highly variable and the differences amongst forecast guidance is fairly significant with regards to timing and location of upper level and surface features. While the upper level pattern is expected to shift east with time for the latter part of the week...what exactly happens with progression of the pattern is yet to be seen. For example, the 10/00Z GFS is the most aggressive with the pattern aloft, with a cut- off upper low tracking tracking across the Mid-Atlantic on Thursday with secondary surface low cyclogenesis ongoing right along the Mid- Atlantic coast. This scenario would likely bring widespread impacts of some sort to the area. Meanwhile, the 10/00Z ECMWF and CMC are both less amplified and aggressive with the trough, simply swinging the base of the trough off the coast with any secondary low development shunted well out into the western Atlantic. This scenario would likely equate to minimal impacts to the area. Ensemble guidance though, does support secondary coastal low development, so this system will need to be closely watched over the coming days to see how close this system may be to our coast. For now, have followed closely to NBM guidance which essentially carries a 20-30% chance of rain and/or snow across the entire region Wednesday night into Thursday night.