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Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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795 FXUS61 KPBZ 131141 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 741 AM EDT Sat Jul 13 2024 .SYNOPSIS... A more active weather pattern featuring increased thunderstorm chances and the potential for severe weather is favored starting Sunday evening through Wednesday. Heat risks will remain elevated during this period as well. Dry and seasonable weather is likely late next week after the passage of a cold front. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Above normal temperature will continue with plenty of insolation. - Isolated afternoon convection can`t be ruled out, but probabilistically is unlikely today. ------------------------------------------------------------------- 7am Update - The forecast for today remains on track. Despite a few convective speckles in the CAMs this afternoon, still think the relatively dry column, weak shear/lapse rates, and notable warm layer near 600mb will suppress any development this afternoon. The HRRR is particularly (over) aggressive at mixing out dewpoints into the lower 50s this afternoon, which would certainly preclude any pop-up showers reaching the ground. Previous Discussion... Aside from subtle height rises, little has changed in the synoptic environment today as a warm but relatively dry airmass remains in place. Though diurnal heating will foster afternoon cumulus, plenty of insolation will ensure another day with high temperature in the upper 80s to lower 90s. There remain hints of isolated afternoon convection by various CAMs either along the WV higher terrain or near a potential Erie lake breeze. Despite potential for near 1000 J/kg mean CAPE, factors like the remaining presence of a notable warm layer near 600mb (see 00z sounding), lack of greater column moisture, and weak shear/lapse rates all lend to too low of a probability of occurrence for mention in the forecast. Any storm threat will quickly end after the sun sets and the surface inversion develops. && .SHORT TERM /SUNDAY 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. ------------------------------------------------------------------- Slight shifting of the surface ridge SE in response to shortwave movement over the western Great Lakes will foster weak warm advection into the Upper Ohio River Valley Sunday. This will trend area temperature toward the lower to mid 90s and foster at least a low probability for locations to be near 100 degrees for heat indices. That shortwave movement will approach the region late in the day and will be responsible for the encroachment of an MCS from the northwest. Initial CAM analysis suggests the prior warm air aloft and dry environment favors weakening of the MCS, meaning Sunday night may either remain dry or just see areas of light rain showers plus increased cloud cover. Crucially, this first shortwave/decaying MCS is pegged by models to help erode/cool the warm air aloft and serve to prime the region for additional shortwave movement Monday. Ensembles are trending toward higher probabilities for showers and thunderstorms ahead of that wave Monday, but much variation remains (and will be tethered, in part, to upstream convective evolution). Current consensus favors an afternoon timing where mean SBCAPE values will range from 2000-3000 J/kg, weak shear and DCAPE values around 1000 J/kg; these components lend to a damaging wind (and lower probability hail threat) via either individual storm clusters or a secondary MCS. Timing and presence of convection will also greatly determine the extent of potential heat risks. The lack of convection and cloud cover through a portion of the afternoon could foster mid 90s highs with rising dewpoints creating fairly widespread heat indices above 100F; early convection and/over lingering cloud cover may make it difficult to even hit 90. && .LONG TERM /TUESDAY THROUGH FRIDAY/... KEY MESSAGES: - Active weather with the potential for severe hazards remain possible Tuesday into Wednesday until the passage of a cold front. - Heat risks could be maximized Tuesday, but will be dependent on convective evolution and resultant cloud cover. - Dry weather and seasonable temperature are likely to end the work week. ------------------------------------------------------------------- Ensembles favor additional shortwave movement south of a deepening upper level trough north of the Great Lakes Tuesday into Wednesday. The more well developed trough is then favored to push a cold front through the region Wednesday afternoon/evening and position broad upper troughing over the Great Lakes to end the work week. In a broad sense, this pattern lends to a peak in hot/humid conditions and potential severe weather Tuesday; peak shower/thunderstorm chances Wednesday with frontal passage; and dry weather with seasonable temperature Thursday into Friday. It remains hard to discern thunderstorm coverage, timing and scope of potential severe threats as subtle variations in shortwave positioning and potential weak ridging between waves remains large among ensemble model solutions. And as has been previously stated, prior days` convective evolution will have significant influence on Tuesdays/Wednesdays outlooks. But awareness of potential hazardous conditions remains a necessity as there is a potential widespread damaging wind threat and/or fairly widespread heat advisory day Tuesday. The best course of action will be to continue to monitor the latest updates and see what trends in model depictions suggest. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Mainly VFR conditions are forecast over the next 24 hours as high pressure remains in control. Patches of mid clouds this morning will give way to scattered afternoon cumulus in daytime mixing. An isolated shower cannot be totally ruled out, but chances of impacting any TAF site are too low for inclusion. Wind will remain generally light and variable. .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...Frazier NEAR TERM...Rackley/Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...CL/88