Timberline Ski Resort Snow Report

648 FXUS61 KPBZ 120707 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 307 AM EDT Sat Sep 12 2026 .WHAT HAS CHANGED... The Flood Watch has been expanded to the rest of the forecast area. Isolated severe storm threats also now encompass more of the area today. && .KEY MESSAGES... 1) Widespread rain and isolated thunderstorms expected on Saturday with flooding and isolated damaging gusts possible 2) Still benchley for severe thunderstorms Sunday afternoon and evening with a cold front, but the level of the threat is uncertain 3) A brief bout of dry weather returns early next week && .DISCUSSION... KEY MESSAGE 1... A renewed push of moisture is forecast today in strengthening south/southwest flow. This is occurring ahead of a shortwave trough that is riding up the Ohio Valley and will cross our region during the late afternoon and evening. Expected precipitable water values of 1.8 to 2.0 inches during this period represent values above the 98th percentile areawide. With initial high clouds providing only modest hindrance to heating, no capping of note on model soundings, and increasing support for lift from warm advection and the approaching wave, CAMs suggest that scattered showers and thunderstorms may begin to fire during the late morning and early afternoon hours. The environment will already be supportive of warm rain processes at that point given the increasing PWAT, increasingly saturated column, and rising warm cloud depths. As the afternoon wears on, these factors continue to improve, and a more robust shield of rain and embedded thunderstorms is likely as the shortwave approaches. Areas east of Pittsburgh may see enhanced low-level convergence as strengthening south/southwest flow butts up against southeast flow just to our east as surface high pressure moves further away from the New England coast. This could locally enhance rainfall rates to concerning levels. HREF probabilities of greater than 1" are generally 60 to 90 percent in the previous Flood Watch areas, with maximum 24-hour rainfall totals ending at 06Z Sunday showing several 3-5" bullseyes. 24-hour LPPM values of 2-4" focus especially on areas northeast of Pittsburgh. Such totals represent the high-end scenario, but the environment is certainly capable of supporting them. While these areas have the highest risk of flooding, elected to expand the Flood Watch to the rest of the CWA. Much of the CWA has soil moisture levels in excess of 50 percent according to MRMS, including portions of eastern OH/northwest PA not previously covered by the Watch. Although low-level forcing may not be as robust as areas to the east, the same favorable environmental parameters for heavy rain (high PWAT/saturated soundings/etc) are present, and at least isolated flooding issues are possible. WPC has expanded the Slight Risk for excessive rainfall to virtually all of the forecast area. In addition to the flooding threat, a window for strong to isolated severe thunderstorms exists. Joint 10km neighborhood probabilities of 1000 J/kg of SBCAPE and 30 knots of 0-6km shear reach the 60-80 percent level across much of the area during the noon to 6 PM period. While mid- level lapse rates will be poor and soundings eventually lead to tall and skinny CAPE profiles, there may be enough storm organization and steep low- level lapse rates to produce damaging wind potential, with small-scale bowing structures possible. Even a tornado cannot be totally ruled out, thanks to the low-level southeast flow noted above allowing for backed surface winds. The heavy rain threat should begin to wane during the late evening/midnight period as the shortwave crosses, leaving some scattered showers in its wake. Lingering low-level moisture should lead to abundant stratus coverage by Sunday morning. KEY MESSAGE 2... Another severe storm threat could emerge on Sunday, as developing Great Lakes troughing drops a surface cold front into our region during the late afternoon and evening hours. The trough will provide sufficient deep shear on the order of 35-45 knots, with higher values closer to the lakes. Moisture certainly remains present with surface dewpoints remaining in the upper 60s to around 70. However, there remains some question as to the level of clearing and thus destabilization that can take place, as ensembles continue to suggest a range of sky cover outcomes. This results in 25th/75th percentile SBCAPE spreads of below 500 J/kg to above 1100-1200 J/kg. Also, the subsident warm layer at 800mb noted by the previous shift continues to show up in some HREF members, but not the RRFS. Thus, uncertainty in the level of severe threat continues. However, the front and the level of shear do suggest that even lower-end CAPE levels may not be sufficient to totally suppress convection, and some CAMs do show at least widely scattered storm coverage during frontal passage. Given the shear, any storm will be capable of marginally severe wind and hail threats. A more widespread threat could emerge if later runs show better potential for destabilization and a lack of capping. KEY MESSAGE 3... Minor timing issues remain, but the trough axis is still slated to cross the region at some point Monday. At least scattered showers will likely linger through Sunday night and perhaps into Monday morning, before mid-level ridging provides a dry interlude by Monday afternoon. This break may last until Tuesday night or Wednesday, depending on the progress of the next front. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... VFR conditions and light wind continue for most of the region through sunrise, but some patchy valley fog may be possible at a few terminals. Mid and upper level clouds will thicken in increasing southwest flow aloft. Increasing low-level moisture and a shortwave riding up the Ohio Valley will support shower and thunderstorm development starting by late morning/midday. Initial coverage will likely be scattered, and is handled by PROB30 groups initially. However, the approaching shortwave and increasing low-level convergence should supports the development of more widespread activity by the mid to late afternoon hours. Efficient rainfall production is expected, with moderate to heavy rainfall rates suppressing visibility to MVFR and even IFR at times, especially east of PIT. Relatively wind TEMPO windows were used for this activity. The storms may also produce isolated strong wind gusts, perhaps 35 to 45 knots at the high end. Even away from the heavier storms, ceilings will eventually fall to MVFR levels by sunset. Past 00Z, rain coverage will slowly wane from west to east as the shortwave departs. However, restrictions will likely continue, as abundant low-level moisture supports stratus development and likely IFR conditions by the end of the TAF period. Outlook... Restrictions will likely continue into early Sunday before some improvement. A crossing cold front may provide at least scattered restrictive thunderstorms Sunday afternoon and evening. A drier period commences Monday, although late night/morning restrictions in fog will remain possible Monday and Tuesday mornings. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...Flood Watch from noon EDT today through late tonight for PAZ008-009-014>016-021-022-029-031-073>078. OH...Flood Watch from noon EDT today through late tonight for OHZ057>059-068-069. WV...Flood Watch from noon EDT today through late tonight for WVZ003-004-012-021-509>514. && $$ DISCUSSION...CL AVIATION...CL