A Bermuda High parked off the East Coast is pumping heat and humidity into Virginia. A cold front approaching from the west and north would seem to be a good trigger for storms Saturday except for two things: the upper level support for the front is weak and the upper air temperatures are pretty warm.
Here’s the surface-based CAPE (instability) map for 5 pm Saturday per the 0Z Friday GFS run:
Forecast soundings yield monster CAPE values of well over 3000 j/kg but very little shear and LCL’s (cloud bases) >1000 meters. That would scream H-A-I-L given potential updraft strengths but not tornadoes. However…there’s the cap.
Surface convective inhibition is pretty robust with this air mass plus there’s a stout cap at the 800-700 mb level. IF this cap can be overcome by an updraft (perhaps along the slopes of the Blue Ridge) there could be an awesome storm or two, especially in northern VA closer to the front itself. I’m still withholding judgement on whether to chase Saturday afternoon as there’s a very large potential for a bust. Need more data!
Meanwhile another – stronger – cold front will approach from the west on Monday. There are concerns about a persistent overcast that would suppress CAPE but shear values will be better. Monday looks like a more promising chase setup and we’ll be talking about it on a Google Hangout Sunday evening at 8 pm (https://youtu.be/UeOF9mtx1ZA).