Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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494 FXUS61 KPBZ 122249 AAA AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 649 PM EDT Fri Jul 12 2024 .SYNOPSIS... Above-average temperatures are expected through early next week before a cold front returns more seasonable temperature late week. A more active pattern is expected Sunday through midweek, favoring increasing chances for thunderstorms each afternoon. && .NEAR TERM /THROUGH SATURDAY/... KEY MESSAGES: - Temperatures trend warmer with heat risk becoming moderate by Saturday. - Isolated convection is possible, but unlikely each afternoon. ------------------------------------------------------------------- For the evening update...removed mention of PoPs as strong subsidence and deep mixing, bringing drier air to the surface, is dissipating any activity that moves toward the CWA. Rest of the forecast is in good shape. Previous discussion... With little environmental change overnight, patchy river valley fog is likely once again. The biggest limiting factor will be any lingering mid-level clouds associated with the passage of the upper trough axis. The warming trend continues on Saturday as broad zonal flow and rising heights aloft drive much of the region back in the 90s. Minimal forcing and warm air aloft should largely suppress most convection, but CAMs do still hint at enough surface heating Saturday afternoon for destabilization. The main triggering mechanism for any convection would be an Erie lake breeze. The result could be brief, isolated thunderstorms favoring northwest PA in the afternoon, quickly collapsing after sunset. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... KEY MESSAGES: - Increasing heat risk expected as temperatures sit 5 to 10 degrees above the daily average. - A more active pattern begins Sunday with a series of crossing shortwaves and possible MCSs. ------------------------------------------------------------------- A more active pattern begins Sunday as the first in a series of shortwave troughs crosses out of the Great Lakes. CAMs highlight a possible MCS crossing out of Michigan and into northern Ohio during the early afternoon hours, eventually decaying as it moves across our area late afternoon or early evening. Some scattered convection may also be possible ahead of this feature, and CAM soundings indicate a possible downburst environment with significant DCAPE near 1500 J/kg. However, considerable uncertainty remains with this setup. In particular CAMs tend to perform poorly with MCSs in a weakly forced environment. Destabilization ahead of the MCS will also depend on the amount of surface heating and moisture availability given lingering warm air aloft and the lack of notable moisture. This could be hampered by increasing cloud cover, though current forecasts put much of the area in the 90s by mid-afternoon. CSU-ML probabilities extend a 5-15% area into eastern OH and most of WV/PA. A similar, but possibly more potent, setup is expected on Monday as another shortwave crosses out of the upper Midwest and through the Great Lakes region. This pattern will again be conducive for MCS development somewhere upstream and moving towards our area during the day. Considerable uncertainty remains and will likely be dependent on Saturday`s evolution, but it`s worth noting that the CSU- MLP highlights an area of 30-45% severe probs into eastern Ohio. This will certainly be something to watch as we get in range of the CAMs. Regarding temperature, the warming trend continues through the short term, with much of the area from PIT south solidly in the mid-90s by Monday afternoon. Monday`s HeatRisk outlook highlights most of the area as a major risk. However, early afternoon iso/sct convective development or an earlier arriving MCS could suppress these highs a bit each afternoon. && .LONG TERM /TUESDAY THROUGH FRIDAY/... KEY MESSAGES: - An active severe weather pattern is anticipated through Wednesday morning, subsiding thereafter. - Heat risks could be maximized Tuesday, but will be dependent on convective evolution and resultant cloud cover. ------------------------------------------------------------------- The basic synoptic pattern continues through midweek as shortwaves continue to cross the area. Models continue to highlight MCS movement near or through the region on Tuesday before a surface cold front passes Wednesday. Uncertainty remains high as Tuesday`s environment will once again be predicated on the previous day`s convective evolution. Prior to the cold front passage Wednesday, the hot and humid environment may also lead to notable heat risk for the region as air temperatures on Tuesday again approach the mid 90s and heat indices cross the 100 degree Heat Advisory threshold. The main limiting factor is potential for thunderstorms to shut-off daytime heating and/or provide excessive cloud cover that stunts surface warming. Ensembles favor the cold front passing Wednesday, but spread exists in the shape of the upper trough and how quickly drier/cooler conditions return for all locations. Most locations should experience dry and seasonable weather Thursday, but storm chances may linger in southern zones if the front ends of stalling south. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... VFR forecast through the period. Much of the cu will dissipate later this evening. Fog is still a threat early Saturday morning, but less so as temperatures have warmed about 10 to 15 degrees higher today. Have included the mention of fog at FKL and DUJ with FKL possibly seeing LIFR fog shortly before sunrise. Any late night fog will quickly burn off after sunrise. More cu is anticipate on Saturday as surface dewpoints rise and moisture increases above the BL. .Outlook... Ensembles favor VFR prevailing through Sunday outside of overnight/early morning patchy fog. The likelihood of restrictions with convection will increase Monday and Tuesday. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Rackley NEAR TERM...Rackley/22 SHORT TERM...Rackley LONG TERM...Rackley/Frazier AVIATION...22