... Scattered shower and thunderstorm chances continue into this evening. As a trough lifts out and as high pressure develops, drier weather with seasonable temperatures will take hold by the end of the week. This dry break will be short-lived as unsettled weather returns during the weekend.
NEAR TERM /UNTIL 6 PM THIS EVENING/... Another day under the northeast CONUS trough means another day with below-normal temperature and scattered showers/isolated thunderstorms. Activity is starting to bloom once again as convective temperature thresholds are reached. Eventually expect the best coverage to be realized to the northeast of Pittsburgh, where weak vort maxes will be rotating through the trough. Kept a mention of isolated thunderstorms, although marginal instability/lapse rates will keep thunder isolated. Flow remains weak overall and storm motions will be slow, and thus cannot rule out one or two instances of localized heavy rainfall, despite non-excessive precipitable water values of around an inch.
Activity will once again diurnally decrease this evening, and some clearing will occur as convective clouds collapse and as the stubborn trough finally begins to lift out of the region. Given cool temperatures and a moist ground, some areas of fog are likely to develop in areas that can clear, although coverage of this remains uncertain. Cooler-than-normal temperatures in the 50s are forecast.
SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... 500mb heights finally begin a slow rise this period, as the trough starts to pull out and the upper low reconsolidates over New England. Although precipitation coverage on Thursday will be lower than in recent days, some modest instability and weak vort maxes rotating through the diminishing trough will still support an isolated shower/storm chance, mainly to the north and east of Pittsburgh.
Any influence of the trough will finally be gone by Friday, as mid- level ridging develops briefly, leading to a mostly dry forecast for the vast majority of the forecast area. The lone exception may be along the east-facing slopes of northern West Virginia. This area may be close enough to a weak surface inverted trough to promote southeast upslope flow, which could work in tandem with increasing moisture to promote a few showers or thunderstorms. These low rain chances may spread to other locations south of Pittsburgh as the moisture and warm advection lift north.
With the departure of troughing and the trend towards quasi-zonal or weak ridging, temperatures will rise back towards climatology for Thursday and Friday.
LONG TERM /SATURDAY THROUGH TUESDAY/... A fresh upper low will drop into the Upper Midwest on Friday and meander around the Upper Mississippi Valley on Saturday. It will then begin to fill as it slowly transitions eastward, finally arriving in the middle and upper Ohio Valley at some point during the first half of next week. Models/ensembles disagree a bit on this timing, but what seems clear is that a period of unsettled weather is in the cards for the extended period, with daily shower and thunderstorm chances. Temperatures will be near or just below seasonal values throughout.