FXUS61 KPBZ 200621 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 221 AM EDT Wed May 20 2026 .WHAT HAS CHANGED... The Marginal Risk area for severe storms today has expanded back northwest slightly, but still remains well south of Pittsburgh. Confidence in a quite wet Memorial Day weekend continues to increase. && .KEY MESSAGES... 1) A conditional threat of isolated severe thunderstorms with damaging wind gusts exists southeast of Pittsburgh this afternoon. 2) Confidence in soaking rainfall during the Memorial Day weekend continues to increase. && .DISCUSSION... KEY MESSAGE 1... Some scattered showers continue across the region during the early morning hours in a moist environment with lingering outflow boundaries. More concentrated showers and thunderstorms are expected to arrive after sunrise as a weak shortwave rides northeastward ahead of a cold front that is slated to cross today. The front should be draped across the northwestern portion of the CWA at 12Z, and should cross through the Pittsburgh area around midday. Ongoing rain and cloud cover ahead of the boundary lend some uncertainty to the amount of destabilization that will be able to occur over our southeastern counties this afternoon. REFS guidance suggests 500-1000 J/kg of surface-based CAPE by 18Z in this area, while the HREF goes a little higher in Preston/Tucker Counties, furthest ahead of the front. Shear in the 0-6km layer in this area is not too impressive, remaining under 30 knots ahead of the front, which will limit storm organization. Still, there may be a relatively brief window during the mid-to-late afternoon for tall storms to take advantage of marginal DCAPE to produce isolated strong to damaging gusts. Hail appears to be a secondary threat due to generally poor mid-level lapse rates and the limited shear. SPC has issued a Marginal (level 1 of 5) Risk for areas southeast of a rough line from Connellsville PA to New Martinsville WV. The passage of the front should end any severe threat by 00Z. Some very localized instances of heavy rainfall are also possible with these storms. Cloud-layer flow will be largely parallel to the front, which could encourage storm training. Also, expected precipitable water values of 1.5 to 1.6 inches is at the very top of climatology. HREF/REFS max precip potential suggest localized 1.5- 1.75 inch totals are not out of the question in northern West Virginia. Still, 3-hour FFG values are generally near or just above 2 inches in this area, and thus anything more than an isolated water issue or two is not expected. KEY MESSAGE 2... The front may waver near the southern reaches of the CWA through Thursday night, keeping occasional rain chances in the forecast, especially south of I-70. The environment favorable for strong convection and heavy rainfall will have departed though, and no major impact from this activity is expected. Memorial Day weekend continues to look quite wet overall. Surface low pressure lifts northeastward into the lower Ohio Valley to our west Friday into Saturday, bringing the boundary back north as a warm front and pushing a broad inverted trough into our region. This should return anomalously high precipitable water values back north, accompanied by broad isentropic lift. Also during this 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. Nevertheless, the NBM continues to illustrate a 60-80% chance for at least aninch of 24-hr rainfall accumulation Friday into Saturday, and a 20-50% chance for 2+ inches. A second wave of rain is then forecast Sunday into Monday though that one appears a bit more progressive in nature thanks to a potential Great Lakes shortwave that has some forward momentum. NBM probabilities for an inch top out in the 20-30 percent range between 12Z Sunday and 12Z Monday. When looking at the total 72-hour period from 12Z Friday to 12Z Monday, the NBM has a 50 to 65 percent chance for 2 inches or more of rain across the majority of the forecast area. Extended machine-learning guidance suggests severe weather chances remain quite low through this period, so that aspect is of lesser concern. However, MMEFS river guidance does suggest some potential impact on area rivers by early next week in higher-end precipitation scenarios, with a number of forecast points on the larger rivers potentially reaching action stage. This also suggests that flooding issues on smaller streams and creeks may become an issue in time. It is too early to discuss specifics and forecast details are yet to be solidified, 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...CL/Cermak AVIATION...WM