Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
039 FXUS61 KPBZ 201152 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 752 AM EDT Sun Sep 20 2026 .WHAT HAS CHANGED... Updated aviation section for 12z TAFs. && .KEY MESSAGES... 1) Rain chances return today and continue into early next week. Longer duration rainfall totals could be high and lead to localized flooding and/or river rises 2) Much cooler temperatures arrive by mid-week && .DISCUSSION... KEY MESSAGE 1... It seems another period of active and wet weather is upon the region. The upper pattern features a continued flatten ridge aloft over the eastern CONUS with another shortwave trough approaching the region. The patten sets up a storm track across the Midwest and into the Upper OH Valley. This will keep a series of shortwave trough approaching the area through the middle of next next week. Addressing the Saturday night into Sunday threat, showers and thunderstorms are tracking across Ohio and mainly sliding just south of the forecast area. There are some scattered development tracking just north of I-70 but this rainfall is not expected to be impactful. The amount of instability is below 500 J/Kg and mainly a flood threat is expected at this point through dawn. By the 10Z to 16Z period additional development is expected into central Ohio with PWATs at 1.8 to 2.0. Plenty of moisture to work with and the NBM giving a 90th percentile amount through the day on Sunday looks to be around 0.75 to 1.50 as a swath of heavy rainfall lines up from just south of PIT and south into the WV counties in the north. The 90th has potential given the amount of moisture in the air. The only hindrance in reaching these values is the amount of instability available. This looks to be a 24 hour probability and would lead to at least a few issues through the day. On another note, the CAMs and ensembles are not handling the amount of rain potential very well, although the track seems to have slide south increasing confidence in a southern Flash Flood Watch and one may be needed for the next round since the soils would be primed. The severe threat for Sunday seems to focus mainly in the morning with the initial rainfall as profiles would show deep saturation and no dry air. If a storm does develop, the main threat would be damaging winds. The Sunday night period will feature another round of rain crossing the southern portion of the forecast area. This third or even fourth round of rain would begin to cause some concern in flooding across the area south of Pittsburgh. The Monday period will feature some showers across the area but will be concerning given the amount of rainfall since Saturday night. It seems that even Monday will need to be monitored for the potential of flooding. Following a brief lowering of rain chances early Monday, it`ll remain active into the middle part of the week. While the setup doesn`t appear to favor heightened flash flooding concerns any given day, long duration accumulation has the potential to be more notable. Latest NBM 48 hour QPF from Monday morning - Wednesday morning has the highest values south of Pittsburgh where a slow moving/stalled boundary is progged to be. Location of that will be paramount for who gets the bulk of the rain, and right now, most ensembles place it south of Pittsburgh. Mean values are around 1.25- 1.5" there, and 90th percentile values up to 2-3.5". Farther north, the mean is much less at 0.5-0.75" with the high end around 1.5-2". There are even some solutions (mostly a southward displaced boundary) in which the northern part of the area sees very little rain. While this all told wouldn`t pose as much a threat for flash flooding, areal flooding and river flooding chances may increase especially if the high-end potential is realized. The primary way to realize that high end potential would be to be positioned immediately north of the stationary boundary with overrunning, and/or on the northwest side of a developing coastal low. Should the stationary boundary be too far south or the coastal low to far east, these threats would not be realized. The area with highest potential for impacts will be south of Pittsburgh and will need continued monitoring into early week. KEY MESSAGE 2... The other story of the week is going to be the much cooler air in place with several days where the highs may not get out of the 50s for some. Surface high pressure across New England will induce stout, prolonged east-northeast flow locally. NBM probs for daytime highs exceeding 65F is basically a 50/50 shot from the ridges to Pittsburgh, then a bit higher farther west, all that with a summertime-biased NBM and likely a bit too high even at that; AI guidance and some deterministic models are running a handful of degrees cooler. Normal highs are in the low 70s and lows in the low 50s throughout next week, so while lows should be right around normal, we could be looking at highs some 10 degrees below. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... MVFR to IFR ceilings in place this morning and should improve to mainly MVFR by late morning before going back to IFR tonight. Probability of LIFR is roughly 20-30% tonight before slightly drier air starts to work into area on northeast winds by early Monday. Areas south of PIT will be wettest over the next 24 hours with rounds of showers this morning and again tonight. Thunderstorm chances will be highest at ZZV HLG MGW and least over the northern airports. Outlook... Restrictions will likely continue into Tuesday and perhaps Wednesday with sufficient boundary layer moisture impacting low level clouds. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ DISCUSSION...Shallenberger AVIATION...Craven