FXUS61 KPBZ 210638 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 238 AM EDT Sun Jun 21 2026 .WHAT HAS CHANGED... Rainfall totals from Sunday night through Monday night have trended a bit lower, and uncertainty remains on where the axis of heaviest rainfall may set up. Isolated instances of flooding and/or severe thunderstorms remain most likely to the southeast of Pittsburgh. Morning fog coverage was also expanded a bit from the previous forecast. && .KEY MESSAGES... 1) Dry weather into this evening. Areas of valley fog this morning. 2) More widespread rain chances return Sunday night and Monday. There is high confidence in a soaking rainfall, but low confidence in the threat of flooding. && .DISCUSSION... KEY MESSAGE 1... Once remaining showers exit Tucker County by 08Z or so, mostly dry weather is forecast into the evening hours as surface high pressure and flat mid-level ridging cross our region. Cloud cover will be on the increase through the afternoon and evening as upper- level moisture increases ahead of surface low pressure, which will enter the Lower Ohio Valley by 00Z. Areas of fog, mainly in valleys, have formed mainly in locations that received rain during the afternoon and evening hours of Saturday. Fog is not expected to become dense on a widespread basis, but will be monitored for potential SPS issuance if areal coverage increases. The fog should quickly lift by mid-morning. KEY MESSAGE 2... The surface low slowly rides up the Ohio Valley tonight and through Monday, likely crossing into central Pennsylvania after 00Z Tuesday. This in turn keeps the associated warm front from pushing as far north as model runs a couple of days ago suggested, perhaps not much farther north than the Mason-Dixon Line. This could have implications for where the heaviest band of rainfall sets up into Monday evening. Despite this, precipitable water still surges into the 1.6 to 1.8 inch range per HREF/REFS. The component models of these ensembles are a bit inconsistent as to where the heaviest band of precipitation is likely to occur. Interestingly, as most of the event now lies within the ensemble windows, heavier precipitation totals seem more likely to be confined mostly to areas south of I-70, where 90th percentile rainfall totals exceeding 1.5 inches are most prevalent in both ensembles. These totals are lower than NBM progs were suggesting a couple of days ago and seems tied to the more southerly warm front position. Given the uncertainties and apparent lowering potential of higher-end rainfall totals, will be holding off on a Flood Watch issuance for now. Any flooding threat may be tied to smaller-scale storm training near the boundary. Model soundings do suggest potential for efficient rain production given the higher PWAT, profile saturation, and deep warm cloud depths. WPC maintains a Slight (level 2 of 4) Risk for excessive rainfall southeast of a HLG/AGC/IDI line. The potential for at least isolated severe storms will need to be monitored as well. SPC maintains a Marginal (level 1 of 5) Risk just to the southeast of the Slight Risk of excessive rainfall noted above. With the warm front in the region during the morning, backed low-level flow and deep shear of 30-40 knots create some impressive-looking hodographs, although whatever meager CAPE there is at that time is likely to be elevated. Still, this will need to be monitored, as any surface-based buoyancy developing earlier than anticipated could result in an isolated tornado threat. While buoyancy may improve during the midday and afternoon hours, veering low-level flow leads to more unidirectional hodographs during peak heating, making damaging wind gusts the most likely isolated severe threat by that time. There remains some question as to how much surface heating can occur, depending on cloud breaks between showers/storms. Coverage of showers/storms will decrease from west to east Monday night with the departure of the surface low, setting up a drier pattern and near-to-below normal temperatures for the middle of the week. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... The main issue early on will be valley fog, mainly in areas that received showers and thunderstorms Saturday afternoon and evening. Conditions may vary between MVFR and LIFR at ZZV, FKL, and DUJ, with some lighter MVFR fog possible at LBE and MGW closer to sunrise. Other sites are not expected to be impacted by fog at this time. Any fog should lift by 12Z on this longest day of the year. Otherwise, VFR conditions and dry weather is anticipated for most of the TAF period, save for perhaps the first showers arriving after 04Z Monday at ZZV ahead of an advancing surface low. Before then, cloud cover will mainly be limited to the middle and upper-level variety as slow warm advection ensues later today. Model cumulus rule does suggest some scattered development this afternoon mainly north of PIT that would collapse with sunset. Thanks to crossing surface high pressure, surface wind will generally remain under 10 knots out of the W and NW. Outlook... Probabilities favor overnight Sunday into Monday for widespread showers (low probability thunderstorms) resulting in MVFR/IFR restrictions as a deeper trough/surface low combo travels through the Ohio River Valley region. VFR conditions are likely to return Tuesday, save for perhaps another round of morning fog. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ DISCUSSION...CL AVIATION...CL