Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
805 FXUS61 KPBZ 041145 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 745 AM EDT Mon May 4 2026 .WHAT HAS CHANGED... Aviation discussion updated for 12z issuance. Otherwise, no major changes were made to the forecast. && .KEY MESSAGES... 1) Shower and thunderstorm chances increase late this afternoon/evening. 2) An active pattern will keep shower and/or thunderstorm chances in the forecast through the weekend. 3) Potential for frost returns Thursday night, mainly across I-80 corridor and in the ridges. && .DISCUSSION... KEY MESSAGE 1... Mainly dry weather is expected into this afternoon, though a few sprinkles or isolated light showers are possible with warm advection. Diurnal instability is expected to build in the warm sector on through the day as a shortwave trough approaches. ML CAPE is progged to reach around 1,000 J/kg across Ohio during the afternoon, with lesser amounts to the east. Shear is also expected to increase, with 30-35kt from 0-6km. A few strong storms with wind and hail will be possible, especially across Ohio, before a general decreasing trend occurs through the evening and overnight as instability gradually wanes. Latest CAMs have been fairly reluctant to initialize showers/storms over eastern Ohio late this afternoon/evening, so it is possible we see only a few isolated non-severe thunderstorms. KEY MESSAGE 2... Surface low pressure will cross north of the Great Lakes today and Tuesday, slowly dragging a cold front into the region Tuesday. Boundary-parellel flow will slow progression of the front as it sinks across our area late Tuesday and Wednesday. Tuesday should be the warmest day of the week, with gusty south wind ahead of the front. Instability is expected to be limited as the front crosses the region, though a few thunderstorms are possible. At this time there is an 80-90 percent probability of seeing at least a half inch of rain with this system, with probabilities around 70 percent for an inch of rain north of PIT. Shower chances will continue on Thursday as the front becomes quasi-stationary across the Lower Ohio Valley and Mid-Atlantic region and as a wave of low pressure tracks along it. A shortwave trough should finally drive the front out the area Thursday night into Friday, but lingering upper troughing will maintain shower chances through the weekend. After a warm start to the week, cooler than average temperatures are expected behind the mid week cold front. KEY MESSAGE 3... Potential for light wind and temperatures below 37F ranges from 50-70% across the I-80 corridor and in the ridges Thursday night/early Friday morning. This could lead to frost development for those areas, but will largely be dependent whether or not skies clear overnight. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... VFR is likely to prevail through the entire period. Wind will pick up notably this morning and afternoon out of the southwest with a tightening gradient and momentum transfer in model soundings suggesting at least 20 knot gusts. The strongest low level flow likely doesn`t arrive until the evening hours. Can`t rule out a brief period of enhanced gusts if the arrival of the stronger winds aloft ends up being earlier, but with nocturnal decoupling beginning to occur around that time any window for higher gusts would be brief. Overnight, 925 mb flow ramps up to around 40 knots and 850 mb flow to 45-50 knots. Ensemble guidance continues to suggest decoupling does not occur and gusts continue into overnight hours, despite warm air advection reinforcing a nocturnal inversion just off the surface. The alternative scenario is that we decouple and surface gusts subside, which would then lead to an increasing LLWS threat as sfc-2kft shear strengthens to near or just above 30 knots. There is still a bit too much uncertainty which scenario will play out, which precludes the mention of LLWS in TAFs at this time, but it`s something that will warrant keeping an eye on. With increasing warm advection, some showers may develop in the evening and even potentially lingering into overnight hours (the latter most likely occurring north of PIT). The scattered nature and run to run model inconsistency with timing/occurrence continues to warrant -SHRA mention in PROB30s rather than prevailing groups. If confidence in occurring/timing increases through the day, a more targeted window for prevailing -SHRA may be included. Thunder is possible as well, though with limited available instability and uncertainty regarding whether updrafts are able to get tall enough to exceed -10C in drier mid-level air, the probabilities for lightning are too low to warrant including in the TAFs at this time. Outlook... A few thunderstorms are possible on Tuesday. More widespread restrictions in showers and thunderstorms are likely Tuesday night into Wednesday as a wave of low pressure tracks along an advancing cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ DISCUSSION...WM/Rackley AVIATION...Cermak/MLB