Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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704 FXUS61 KPBZ 121354 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 954 AM EDT Fri Jul 12 2024 .SYNOPSIS... Rising temperature is expected today through early next week before a late week cold front returns seasonable temperature to the area. Confidence is growing for an active weather pattern featuring severe potential beginning Sunday afternoon and peaking Tuesday into Wednesday morning. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Afternoon high temperature will be approximately 5 degrees above the daily average. ------------------------------------------------------------------- 10am Update - River valley fog has dissipated with daytime mixing. The forecast remains on track with quiet, but warm weather today. Previous... Weak warm advection within southwesterly flow will support a return to above normal temperature this afternoon as the region sits east of a saggy western Great Lakes trough. Most locations will be dry but isolated convection entering eastern Ohio zones can`t be ruled out as the trough lifts east, but limited column moisture will keep probabilities low. Additional, surface convergence along the WV higher terrain due to a Carolina coastal low may combine with diurnal heating for isolated afternoon showers/storms. Again, probabilities are low with convection quickly moving east of the region in conjunction with storm layer wind to the NE. Little environmental change to the overnight period should result in patchy river valley fog formation. The biggest limiting factor will be any lingering mid-level clouds associated with the passage of the upper trough axis. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... KEY MESSAGES: - Increasing heat risk expected as temperatures sit 5 to 10 degrees above the daily average. - Low probability thunderstorms possible as a period of a more active pattern begins. ------------------------------------------------------------------- Broad zonal flow with rising heights aloft will support a continuation of rising temperature Saturday, with highs expected to sit 5 to 10 degrees above the daily average. Little to no forcing and warm air aloft should ensure dry weather, but a few convective models hint at enough heating to destabilize the environment (generating ~1000 J/kg SBCAPE) for an isolated thunderstorm. The most likely form of lift will be a lake breeze off Lake Erie providing enough convergence for an isolated shower/thunderstorm. Forecast maintains dry condition based on ensemble means, but trended toward isolated mentioning for northwest PA to capture this conditional outcome. The first in a series of upper level shortwaves dropping southeast over the Rockies ridge will approach the Upper Ohio River Valley Sunday. Its depth and southeast movement/timing will be influenced by convective evolution of likely MCS development beginning in the Upper Midwest. The favored solution at this time has either convective development and continuation of a weakened MCS starting early Sunday afternoon. Lack of notable moisture prior to its arrival and residual warm air aloft will likely keep severe probabilities low, but enough instability from sfc heating (highs will be 5-10 degrees above normal) should lead to scattered thunderstorms coverage. More notably, this shortwave is likely to serve as the primer for a more active weather pattern the following days. && .LONG TERM /MONDAY THROUGH THURSDAY/... KEY MESSAGES: - An active severe weather pattern is anticipated through Wednesday morning, which will subside thereafter. - Heat risks could be maximized Monday/Tuesday but will be dependent on convective evolution and resultant cloud cover. ------------------------------------------------------------------- The basic synoptic pattern evolution will feature a series of shortwaves dropping out of the upper Central Plains through the Great Lakes region Monday through Wednesday and usher a transition to broad upper troughing over the northeast CONUS to end the week. Repositioning of the surface high initially SE is likely to foster a hot, humid environment for the Upper Ohio River Valley thanks to warm, moist southwest surface flow. The combination of the hot/humid environment and upper shortwaves will lead to increase thunderstorm chances that historically see higher probabilities for severe weather. Deterministic and AI-driven models confirm this pattern recognition by portraying MCS movement through or near the region Monday/Tuesday before the surface cold front passes Wednesday. Spread and variations in the outcomes remain high as a given day`s environment will be predicated on prior convective evolution; but enough signal is present to alert for the potential for multiple rounds of severe weather. Prior to the cold front passage Wednesday, the hot and humid environment may also lead to notable heat risks for the region as air temperatures on Monday/Tuesday 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 /14Z FRIDAY THROUGH TUESDAY/... Morning fog mostly confined to river valleys should dissipate by 13Z with the onset of daytime heating and mixing. VFR conditions and light winds prevail thereafter through much of the TAF period. Hi-res models are split on whether there will be enough boundary layer moisture for a fair weather cu field to develop this afternoon. Even if it does form, coverage would be few/sct and cigs around 5kft, resulting in little to no impacts. Ensembles are showing fog potential returning early Saturday morning (similar to this morning), with probabilities topping out around 40-50% for visibilities below MVFR along and adjacent to river valleys from roughly 09Z-13Z. .Outlook... Ensembles favor VFR prevailing through the weekend outside of overnight/early morning patchy fog. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Rackley/Frazier NEAR TERM...Rackley/Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...Cermak