For record keeping purposes, here is a discussion I created at 11:30PM on 6/26/15 for in-house Neoweather viewing regarding Saturday’s severe potential in eastern Ohio
With water vapor imagery showing the trough associated with our storm beginning to slow down and potentially start closing off over IL right now with heights gradually rising ahead of it per mesoanalyisis, am thinking that the continued trend among the short term/hi-res guidance to slow down the low further and strengthen it a bit more isn’t a mirage. This results in the dry slot working farther north into eastern Ohio where modest destabilization looks likely. Although mid-level lapse rates will be poor, rich low level moisture would combine with temperatures in the low to mid 70’s to produce over 1000 J/KG CAPE within the dry slot ahead of the cold front. Temperatures in the warm sector near/south of the Ohio River will struggle to drop below 70 tonight due to high dew points and cloud cover, so it won’t take much surface heating of the warm sector airmass to yield temperatures in the mid 70’s and a half decent amount of instability.
Within the warm sector, surface winds may be backed enough near the warm front on the edge of the dry slot to increase helicity enough for robust rotating updrafts across eastern OH by early to mid afternoon. In addition, 30-40 knots of bulk shear supports storm organization and potential updraft rotation. Although there is pretty good mid-level drying within the dry slot, very weak mid-level lapse rates and fairly high freezing levels will likely limit the hail potential.
Am thinking that if the slower models are right that a few storms or clusters could develop over eastern OH and potentially produce damaging winds given sufficient shear for storm organization and mid-level drying increasing the likelihood for microbursts with any robust cores that develop. Given storm motion will be almost perpendicular to the warm front that will enhance helicity some on the eastern edge of the dry slot/warm sector, I’m not sure that storm residence time will be great enough to capitalize on this increased shear and produce tornadoes along the warm front. However, with reasonably low LCLs and decent 0-3km CAPE per NAM soundings for CAK should temperatures reach the mid-70’s, the potential for a quick spin-up may rise if sufficient surface heating occurs (it won’t take much).
Although the 18z GFS still has a faster surface low and less instability in the dry slot, the slower low/more unstable dry slot is not only supported by the closing off of the upper level trough overhead and strong upper level divergence but also by a plethora of models including the 0z NAM, RAP, HRRR, SREF and 12z ECM. This gives me enough confidence in enough instability developing for a potential severe threat to play out.
Should there be any sun in the dry slot (or should temperatures reach 75+ without it), then NAM soundings suggest DCAPE increasing to 800-1000 J/KG along with moist low levels and nearly dry-adiabatic low level lapse rates, which would potentially support a more robust wind threat. However, there is still enough uncertainty regarding destabilization to go with anything more than a low risk with some bust potential either way.