FXUS61 KPBZ 200503 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 103 AM EDT Wed May 20 2026 .WHAT HAS CHANGED... The forecast remains largely unchanged, with continued confidence in storm arrival in eastern Ohio and northwest Pennsylvania after 8 PM tonight. && .KEY MESSAGES... 1) Highest risk for severe storms/damaging wind gusts will be in areas of northwest PA/eastern OH, with diminishing risk near Pittsburgh. Conditional severe threats remain on Wednesday southeast of Pittsburgh with a departing front. 2) Strengthening signal for a wet Memorial Day Weekend. && .DISCUSSION... KEY MESSAGE 1... Mid-level capping (focused around 500mb per this morning's 12z sounding) is maintained through this afternoon and will keep ongoing isolated to scattered convective activity limited to showers and possibly a thunderstorm or two with a low severe threat. The upper ridge supporting that cap begins to break down in response to an encroaching Upper Midwest/Great Lakes shortwave, with 1500-2000 J/kg of MUCAPE forecast to develop by this evening. A more organized severe thunderstorm threat remains possible in closer proximity to an advancing cold front that enters the area after 8pm. The most likely scenario presented by CAMS remains the development of strong to severe thunderstorms in western Ohio in the 6pm-8pm window along and ahead of the front, perhaps associated with a prefrontal trough. These storms should be weakening as they approach northwest PA/eastern OH after 9pm or so due to diurnal buoyancy loss as well as 20-25 knots of 0-6km shear fostering only loose organization/limited cold pool consolidation. Still, with up to 900 J/kg of DCAPE available north and west of Pittsburgh, strong to severe downdraft winds remain a decent possibility in the taller storms; this is the area highlighted in SPC's day 1 Slight (level 2 of 5) Risk. Hail is a lesser concern due to the lower shear and poor mid-level lapse rates less than 6C/km. Also, with around 100 m2/s2 of 0-1km storm- relative helicity available north of I-80, a tornado cannot be totally ruled out in this area as LCLs lower, although 0-3km CAPE may be a bit low. Convective intensity is expected to wane overnight as the parent cold front moves in, but some showers and storms will continue. Wednesday still presents a limited and conditional severe threat in the Laurels and in the WV ridges. This will depend on frontal timing and the amount of rain/cloud cover in the region during the morning into the afternoon. A slower front, with less precipitation and some cloud breaks out ahead, could allow sufficient destabilization for an isolated damaging wind threat. Scenarios with a faster front and more solid cloud cover could largely choke off the threat for strong convection. This will need to be monitored, and the SPC Marginal (level 1 of 5) risk southeast of Pittsburgh shows the potential threat area well. KEY MESSAGE 2... Probabilities for a soaking rain over Memorial Day Weekend continue to increase as an active pattern persists through that time. Latest guidance suggests a surface low lifts northeastward into the lower Ohio Valley to our west Friday into Saturday, bringing a warm front and widespread rain chances to the region. During that time, surface high pressure is forecast to be centered over the Upper Great Lakes and New England states. This setup is similar to past events that have generated 2+ inches of rainfall across the local area, though it should be noted that minor deviations (e.g., east-west positioning of the low or strength of the ridge) could result in the axis of heaviest rainfall shifting around (or away from) the local area. Latest NBM probabilities show a 60-80% chance for at least an inch of 24-hr rainfall accumulation Friday into Saturday, and a 20-40% chance for 2+ inches. A second wave of rain is then forecast later in the weekend, though that one appears a bit more progressive in nature and NBM probabilities reflect that with only a ~20% chance of exceeding an inch of 24-hr rainfall Sunday into Monday. Still, combined with the preceding Friday-Saturday rainfall, it is looking more possible that weekend totals approach or exceed 1-2 inches, and potentially even 3 inches (20% chance in NBM). It is still too early to discuss impacts as a lot could change over coming days, but this signal will warrant monitoring through the week. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... Showers and a few thunderstorms have continued to diminish for most areas tonight as these have outrun the more favorable instability, looking at the latest mesoanalysis and 00Z instability charts. A cold front will continue to approach the area through morning, with additional showers crossing the area. MVFR restrictions are also expected to develop with increasing low level moisture associated with the front. A gradual decrease to IFR is expected for most ports after FROPA from mid morning into the afternoon. Areas from HLG to MGW will see a potential for a thunderstorm with diurnal instability building ahead of the later FROPA. Included a prob30 at HLG, with a tempo at MGW where there is a higher potential for thunderstorms from mid to late afternoon. A wind shift to the NW, and eventually N, is also expected after the passage of the front. Some improvement back to MVFR is expected by evening, though a crossing wave along the front could spread a few more showers across the region. Outlook... Restrictions will likely continue into tonight with the crossing wave along the front. VFR should return to most airports on Thursday as high pressure briefly builds in from the N, though MGW could see restrictions continue through late morning. Widespread restrictions in rain are expected to overspread the region from S-N Friday into Saturday with a warm front. Some improvement is possible Sunday until a cold front approaches later in the day. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ DISCUSSION...Cermak/CL AVIATION...WM