... Cold front approaches late this afternoon, with severe thunderstorms possible. High pressure returns Saturday. Active weather returns for late in the weekend.
NEAR TERM /THROUGH TONIGHT/... As of 150 AM Thursday...
Patchy valley fog already forming at this hour with clear skies and moist low levels, will continue to expand toward daybreak.
Considerable uncertainty exists regarding potential severe weather late this afternoon into this evening. An upstream mesoscale convective complex moving into NE IA and S WI at this hour is expected to continue to propagate south-southeast through the remainder of the overnight with remnants arriving northwestern portions of our forecast area late morning to noon. Convection allowing models offer a variety of solutions as to how well this holds together and ultimately influences our ability to build instability via daytime heating later this afternoon ahead of an approaching cold front.
A surface cold front approaching the Middle Ohio Valley late this afternoon/early this evening will serve as the focusing mechanism for thunderstorms amid favorable environmental variables for severe weather. MLCAPE values of 1500-2500J/kg and deep layer shear of 35- 40KT will be sufficient for super-cellular storm structures, although given linear forcing this may quickly grow upscale into at least a broken line of convection racing south across the region through the late evening. The main concern with these storms will be damaging winds due to cold pool conglomeration, relatively fast storm motions, and dry air aloft , although a few instances of large hail are also possible especially with any initial discrete convection. Expected linear storm mode and increasing propensity for a transition to elevated convection with southern extent will be a limiting factor for tornadoes, but certainly can't rule out a few spin-ups across SE OH and N WV this evening given low level SRH values in excess of 100 with a rather moist boundary layer in the presence of discrete supercells. Despite aforementioned fast storm motion, high rainfall rates of 1-3 inches per hour could yield some localized flash flooding concerns, mainly over urban or low laying areas, but do not anticipate any widespread issues.
The cold front quickly exits south during the predawn hours taking any severe chances with it. A few hours of post frontal showers appear possible before precipitation comes to an end. Depending on local rainfall totals and some clearing toward dawn, at least patchy fog will be possible heading into Friday morning.
To reiterate, the upstream MCS this morning will likely play a critical role in the ultimate evolution of the severe threat late this afternoon into this evening. Stay tuned for forecast updates.
SHORT TERM /FRIDAY THROUGH SATURDAY/... As of 200 AM Thursday...
Frontal boundary will be across southern zones at the start of the period, with a few lingering showers and storms across the far south. Boundary will continue to sag south during the day Friday, with drier/less humid, and cooler air taking hold for Friday into Saturday.
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 205 AM Thursday...
Late Saturday night into Sunday, a shortwave will move east across the area, creating precipitation chances across the far south. This will be followed by another upper shortwave and surface cold front on late Sunday into Monday. Unsettled, and cooler weather will continue across the area for the remainder of the extended with an upper trough lingering across the area.