FXUS61 KPBZ 181709 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 109 PM EDT Mon May 18 2026 .WHAT HAS CHANGED... On the whole, the forecast remains unchanged, except for higher confidence in an 8p to 2a arrival of storms in northwest PA and eastern Ohio Tuesday night. && .KEY MESSAGES... 1) Heat impacts for sensitive populations continue early this week, with temperatures up to the upper-80s to low-90s. 2) Conditional terrain/lake driven severe chances today, highest severe chances tomorrow evening for NW PA and east OH, and conditional severe threats Wednesday SE of Pittsburgh with departing front. && .DISCUSSION... KEY MESSAGE 1... The 12Z surface analysis has the 587dm height line draped across the area, which generally suggests that upper 80s are most likely for highs today. A non-BC model like the LREF and HREF, generally agree, with the 25th-75th percentile spreads narrow and generally between 86F and 90F. With high confidence in mostly clear skies for most today, its possible these deterministic high tend toward the higher end of the non-BC distribution. So this would generally mean temperatures near-90, with some 90s possible with urban and river-valley terrain influence. Some "cooler spots" into the low-to-mid 80s are favored for high terrain and north of I-80. Highs today will be within a few degrees of record highs for all climate sites. The HREF only alludes to temperatures dropping into the mid-to- upper 60s, which will provide little chance for temperature recovery overnight. This will challenge a few "max-low temperature" records. Mean heights may drop slightly Tuesday with the beginning of a ridge breakdown. Additionally, more mid- moisture will also allow for more cloud cover. All in all, temperatures may be a degree or two cooler in areas that do not see rain, but cumulative heat stress continues. So upper-80s, are again favored for most. The NWS heat risk shows mostly a moderate risk Monday into Tuesday, whereby heat may generally impact the most sensitive populations. Make sure to stay hydrated or monitor for signs of heat illness if spending excessive time outdoors. KEY MESSAGE 2... All of the area will be under the northern periphery of the ridge axis today, with corresponding subsidence enforcing mid- level capping. While diurnal cumulus are developing, as we continue to mix into a dry layer (evidenced on 12Z sounding from 750mb to 600mb), we expect most vertical development to be limited. There's a couple exceptions that will need to be addressed. First will be the high terrain. With ridge-top convergence in mostly NE flow aloft, we coudn't rule out a storm firing in an environment of 1000-1200 DCAPE, which could certainty carry a conditional downburst wind threat in the low probability this happens. Consistently, the highest chance of development has been eastern Tucker County, but with NW flow aloft, the thought would be that the highest risk would be to the east for the forecast area. The second area would be a conditional threat of storm development on a lake breeze this afternoon. This is lower confidence, but should it occur, the same downburst threat is possible, with outflow potentially carrying development into NW Pennsylvania. Both threats are conditional on development (<30% chance), but should development occur, damaging wind risks would increase substantially. A ridge breakdown begins Tuesday, with afternoon storm development in western Ohio likely. The most likely timing of this appears late- day. There's a bit of a conditional risk from 20Z to 00Z, but the current thought is that capping will be too strong to let the environment utilize the ~1500 to 2500 MUCAPE for "bubble-up" convection in NW PA in the afternoon. Later, some combination of outflow from the Ohio convection on a pre-frontal trough and/or a lake breeze will make convection more likely in the 00Z to 06Z window. Since this timing is mostly after sunset, storms are expected to have a decaying trend as they enter the area, but they certainty could be strong enough to produce wind gusts up to 60mph, most likely for the I-80 corridor with DCAPE of 900 to 1000, with threats also possible into eastern Ohio. Convective intensity is expected to wain overnight as the parent cold front moves in, but some isolated showers/storms remain possible. Wednesday will bring more of a conditional severe threat southeast of Pittsburgh, with the main uncertainty being 1) frontal timing and 2) cloud cover. In a scenario with a slower front and limited cloud cover, recovery of instability and a limited severe threat is possible for northern WV and far SW PA. But should the front be faster or clouds complicate instability generation, severe threats are lower. Severe chances taper over the next week. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... High confidence VFR through the TAF period under the influence of high pressure east of the region. A few cu develops this afternoon with peak heating/mixing while southwest winds occasionally gust between 15-25kts. Any convective chances are tied to weak convergence along the WV ridge-line, with storms drift northeast. Recent deterministic models are showing a lower likelihood for this occurring. There is a non-zero chance for isolated showers and thunderstorms develop off its outflow near to after 00z tonight around northwest PA but probability is too low for TAF mention. Nocturnal increases in the low-level jet may create brief periods of LLWS, however, the lack of duration or meeting criteria (either by speed/direction or by height) led to an omission from TAFs. Area mid to high level cloud cover increases overnight into Tuesday morning in association with an eastward moving but decaying MCS. These clouds are expected to dissipate with daytime heating allowing VFR ceilings to persist through the day. Some isolated thunderstorms possible in northwestern PA, however, they were omitted from the TAFs due to <25% probability of occurrence. Outlook... An upper shortwave and surface front will push a shower/thunderstorm axis east Tuesday evening through Wednesday afternoon. Initial restrictions will be tied to rainfall intensities with height falls not occurring until after frontal passage. High pressure and VFR returns by Thursday areawide before an active pattern feature multiple rain chances develops Friday into the weekend. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ DISCUSSION...Milcarek AVIATION...Frazier/Lupo