Scientific Forecaster Discussion
000 FXUS61 KPBZ 170948 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 548 AM EDT Wed Jul 17 2019 .SYNOPSIS... The remnants of Barry will produce periods of showers and thunderstorms through Wednesday night, with locally heavy rain likely. A hot and humid airmass will remain in place through the weekend. && .NEAR TERM /THROUGH TONIGHT/... 530am update... Small tweaks to near term PoP and temps to better capture current radar and sfc ob trends, but the overall forecast message remains the same. Previous Discussion... Widespread showers and thunderstorms are expected through tonight as the remnant wave of Hurricane Barry shifts from Indiana through the upper Ohio River Valley and into the northeast U.S. Storms will become more focused and organized during the late afternoon and evening hours along a cold front that will drop south out of the Great Lakes. Slight drier and cooler air plus NW flow behind the front will end precip chances, with the front moving through the entire area by Thursday morning. The warm, humid environment Today will be characterized by marginal CAPE, weak shear, and notably deep moisture with PWATs 2.5 SD above normal. Expect fairly efficient rain making processes that will allow for significant accumulations in short periods of time, making flash flooding the predominant weather threat for Today. However, given fairly dry grounds resulting in higher FFG and hi-res models lacking enough high QPF signatures, will forego a flash flood watch at this time. A watch may be needed if more training of storms occurs, so radar trends will need to be monitored. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... Brief NW flow behind the cold front and exiting Barry remnants Thursday morning will quickly becoming a building ridge by the afternoon. Building pressure heights will allow for hotter high temperature Thursday despite the cold frontal passage, with most areas above normal. Residual moisture along the eastern ridges into the WV mountains plus daytime heating may allow for a few afternoon thunderstorms. Increasing heights and moist southerly sfc winds are expected Friday into Saturday as the 500mb high becomes centered over southern WV, resulting in hot and humid conditions with little chance for rain outside of iso storms Saturday afternoon. Confidence is high that most locations outside of the higher terrain will reach Heat Advisory criteria (apparent temperature of 100F or higher) both Fri/Sat, with increasing confidence of Heat Warning criteria (105F or higher) for southeast OH into portions of extreme western PA. Social Media and HWO messaging will continue but, given potential impacts with heavy rains Today, will delay any hazard issuance at this time. While low, there is a chance of a storm complex moving out of the Great Lakes and into our northern CWA late Thursday night into Friday. This rain and its resultant cloud cover could also alter the heat advisory potential. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... The ridge will begin to break down Saturday night through Monday as a series of shortwave troughs roll through the region with periods of showers and thunderstorms. The trough axis should dig farther south by Tuesday in conjunction with a sfc cold front, resulting in a return to drier weather and near normal temperature. && .AVIATION /10Z WEDNESDAY THROUGH SUNDAY/... Clusters of showers with very isolated thunderstorms continue to lift across the region mainly north of PIT this morning. Expect this activity to depart by around 12Z, with a very short lull in rain coverage. Most locations will start out VFR, save for early dips to MVFR at FKL/DUJ. Coverage of showers and storms will increase later this morning as deeper moisture and the upper wave associated with the remnants of Barry arrive. Ceilings will likely straddle a low VFR/high MVFR line across the region, with terminals east of PIT most likely to remain with prevailing VFR ceilings. Thunderstorms are expected to form to the northwest along a weak front stretching along an ERI/AKR/CMH line, and head southeast into the region during the afternoon. Timing the period of most impact remains tricky, and elected to continue with prevailing SHRA/VCTS in the TAFs. Any storm could of course provide brief MVFR/IFR restrictions. Precipitation will taper off this evening behind the weak front. Expect ceilings to fall to MVFR and then IFR tonight, with some patchy fog possible as well, as low level moisture remains abundant. .Outlook... MVFR/IFR restrictions may continue into Thursday morning. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None.