Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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830 FXUS61 KPBZ 291248 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 848 AM EDT Sat Jun 29 2024 .SYNOPSIS... The probability of severe weather increases after 12pm today. Torrential rain, tornadoes and damaging wind all will be possible. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Favorable environment for severe weather today. Damaging winds and tornadoes will likely be the main threat, small hail may be observed. - Flash flooding will also be possible due to torrential downpours in the heavier thunderstorms, mainly from the Pittsburgh metro on north. ------------------------------------------------------------------ 8:30am: Isolated showers will continued to develop ahead of an approaching shortwave and cold front this morning. Vertical and directional wind shear is promising based on KPBZ`s vertical wind profile, 0-1km shear is measuring 40kt to 45kts. Instability will increase with moisture air (70F dew points over Ohio) advancing into western PA over the next 3 hours. 12Z PIT sounding currently has MUCAPE near 600J/kg. However, ILN`s sounding (to our west) already has near 1000J/kg. The severe weather threat will likely be ahead or along a mesoscale feature currently in central Indiana. Previous Discussion: Low pressure currently located over the upper Great Lakes has resulted in a broad region of southerly flow setting up across the Ohio Valley and lower Great Lakes regions. This has been ushering a warm and moist airmass northward, effectively helping to moisten not only the surface (dewpoints up roughly 10 degrees from where they were this time yesterday), but the deeper-layer profile as well. Very dry air was still noted on the PIT 00Z sounding in the 700mb-600mb layer, which has helped limit (via evaporation/entrainment) the vertical extent of attempted showers across our area thus far, despite there being plenty of instability. As a result, much of the shower activity has developed to our north and west for now. However, that dry layer will eventually moisten and convection should then expand southward and eastward into our forecast area by dawn, filling in across eastern OH and northwest PA (generally north and west of Pittsburgh). A roughly southwest-to-northeast motion may result in training of showers and storms across these areas throughout the morning, which combined with impressive deep- layer moisture profiles characterized by 2+ inch PWATs, may lead to some flooding issues. A Flash Flood Watch remains in effect for areas north of I-70 until 2AM tonight. Gradually, showers and storms shift eastward, with convective models continuing to suggest some organization into one or multiple line segments that push across the area through the afternoon and evening. The environment ahead of these storms will support thunderstorm intensification to severe levels, with damaging straight line winds being the primary threat. The greatest tornado threat will reside generally north of the I-70 corridor where 850mb and 700mb flow will be stronger, resulting in more bulk shear in the sfc-3km layer. Farther south, weaker winds and a unidirectional wind profile in the low levels appear to reduced the tornado threat somewhat, though steep lapse rates will still promote strong low-level updrafts in thunderstorms which can overcome marginal shear profiles, so the tornado threat certainly is not zero in those areas. The Storm Prediction Center has maintained a Slight Risk (Level 2 out of 5) for severe thunderstorms across the entire area. In terms of timing, the primary wave of thunderstorms carrying the greatest severe threat pushes through between roughly 3-9pm, though there is some indication of weak backbuilding occuring towards the latter half of that window with storms lingering in areas southeast of Pittsburgh until closer to Midnight. Additionally, there may be redevelopment overnight into early Sunday morning along the cold front itself as it pushes through the area. Hi-res guidance suggests a low-end severe threat carries into this overnight wave, though available instability will be heavily dependent upon how worked over the environment is following the evening round of storms and whether enough recovery can occur through warm air advection alone. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... KEY MESSAGES: - A cold front sweeps through the area Sunday morning/afternoon. - A few storms along the front could become strong, primarily east and south of the Pittsburgh metro. Damaging straight line winds will be the primary threat. - Cooler and drier weather expected in the wake of the front Sunday night as high pressure builds into the region. ------------------------------------------------------------------- A cold front enters the area from the northwest around or shortly after sunrise on Sunday. Showers and thunderstorms could be ongoing along the front itself as it pushes through, leading to lingering rain chances across much of the area through the morning hours. The front is not expected to exit to the southeast until early to mid afternoon, which may allow enough destabilization to occur ahead of it to support a few strong thunderstorms that will carry a low-end damaging wind threat, primarily east and south of the Pittsburgh metro. As such, the Storm Prediction Center has highlighted the higher terrain of southwest PA and much of northern WV in a Marginal Risk (Level 1 out of 5) for severe weather. Drier air moves into the area in the wake of the front Sunday evening and Sunday night, as well as cooler temperatures with overnight lows dipping into the 50s areawide by early Monday morning. && .LONG TERM /MONDAY THROUGH FRIDAY/... KEY MESSAGES: - Dry weather expected Sunday through mid week under building high pressure. - Showers and thunderstorms return Wednesday and Thursday with another low pressure system. ------------------------------------------------------------------- Dry weather persists through Tuesday night under high pressure. The upper ridge then pushes off to the east and low pressure moves back into the Great Lakes region, bringing showers and thunderstorms back to the area Wednesday through the end of the week. Temperatures will be below seasonal levels Monday, followed by a warm up back to near or slightly above levels Tuesday through the end of the week. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Much of the forecast remains on track for the early morning period with VFR expected with increasing mid-level cloud coverage as a system approaches from the west, ushering in warm/moist advection. VFR will prevail with moderate to high probability for all airports south of FKL/DUJ for the TAF period well into the warm sector of the passing low. At DUJ/FKL, deeper saturation maintains chances of MVFR for most of the day. Beyond daybreak, shower chances slowly increase from northwest to southeast as pre-frontal convergence is strewn across the area. With increased daytime instability, shower chances transition to storm chances in the afternoon/evening for all ports. Strong to severe thunderstorms are anticipated as the front crosses the area, mainly after 18Z. The first ports to be affect will likely be ZZV, BVI, and FKL. Storms are most likely to finish at MGW around 02Z. The most likely timing for Pittsburgh area ports is between 20Z and 22Z. Low clouds and patchy fog are possible tomorrow night with cold advection and radiative cooling forcing saturation, given recent rainfall. IFR restrictions remain possible, most likely for eastern ports. .Outlook... MVFR conditions may continue north of PIT with lingering low-lvl moisture. Widespread VFR will likely return Sun afternoon under high pressure and is likely to persist Mon and Tue. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...Flood Watch through late tonight for PAZ007>009-013>016- 020>022-029-073-074-077-078. OH...Flood Watch through late tonight for OHZ039>041-048>050. WV...Flood Watch through late tonight for WVZ001-002. && $$ SYNOPSIS...Hefferan NEAR TERM...Cermak/Hefferan SHORT TERM...Cermak/Craven/Kramar LONG TERM...Cermak/Craven AVIATION...Milcarek