Interesting discussion from Mount Holly. Plenty of potential, lots of uncertainty.
One of the more difficult warm season forecasts in recent memory for Thursday, with reasonable outcomes ranging from a largely uneventful day to a fairly high end severe weather event. Synoptically, northwest flow aloft continues. Surface low pressure is expected to track eastward through the Great Lakes in response to a southeastward digging shortwave propagating through the 50 to 60 kt 500 mb flow. Meanwhile, a convectively enhanced wave will likely dive southwest of us on Thursday. This wave will result from explosive convective development and likely derecho formation over the Midwest on Wednesday. This MCS/derecho will probably not be much of a factor for our region, either tracking southwest of us and/or not surviving this far in severe form. The SPC SWODY1 does extend a Marginal Risk into our Delmarva zones on the off chance it does make it all the way to the coast. This feature may also serve to deposit convective debris over our region, which would limit instability for new convection on Thursday. However, anvil level storm relative winds suggest this is unlikely, and that much of the convective debris will probably be shunted south of us. But the evolution of Wednesday`s convection and potential lingering debris and/or outflow boundaries will no doubt have some impact on Thursday. Another complicating factor is much of the guidance indicating fairly widespread but likely non-severe convection over our region on Thursday morning and early afternoon. This is likely in response to retreating high pressure, combined with surface convergence and increased low level moisture in response to a shift to southeasterly flow. This type of weakly forced convection is common in these regimes, and is a common failure mode for severe weather events. If early day convection is as widespread as much of the guidance indicates, I would be doubtful of the afternoon severe potential, especially in eastern portions of the area, even as the better forcing from the approaching mid-level jet and vorticity max arrives. With those caveats mentioned, the dynamics on Thursday are no doubt impressive, unlike any we`ve seen this year in terms of the potential overlap of instability, shear, and forcing if everything comes together right. 28.0z CAM guidance largely clobbers the region with severe convection Thursday afternoon and evening, but run-to- run consistency has been poor. Should several of those 0z CAM solutions (i.e. 3km NAM, ARW) and their associated forecast soundings come to pass, then a significant severe weather event with all severe hazards would be likely. The Storm Prediction Center has added a Slight Risk of severe weather over much of the region.