Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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217 FXUS61 KPBZ 251823 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 223 PM EDT Wed Sep 25 2024 .SYNOPSIS... Gradual lowering of precipitation chances is expected through Thursday before a potentially unsettled pattern develops Friday into early next week. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Scattered showers and thunderstorms continue today. ------------------------------------------------------------------- Broad ascent with weak embedded vortices will promote scattered showers and low probability thunderstorms through tonight ahead of a stalled closed low sitting over the lower Ohio River Valley. A lull between waves (with brief subsidence) is occurring as of 2pm, with an uptick in activity likely between 4pm-10pm as the next shortwave crosses and the weak surface front approaches from the west. Despite 30-40kts effective shear, excessive cloud cover will minimize sfc heating and keep area instability generally below 1000 J/kg and keep lightning (let alone severe) risks low. Dry antecedent conditions and weak convergence also should limit any flooding concerns. Overnight, the closed Ohio Valley low will begin sagging SW toward the western TN while a northern trough shifts toward New England. This will lend to a downward trend in convective activity given than ideal position relative to various waves. Little air mass change and excessive cloud cover will maintain above average temperature. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... KEY MESSAGES: - Mostly dry with seasonable temperature Thursday - Potential for increasing influence from Hurricane Helene ------------------------------------------------------------------- Confidence is high in drier weather developing Thursday as the closed low and remnants of Hurricane Helene remaining well to the south and Nova Scotia troughing displaced northeast. The moist airmass will be relatively unchanged, lending to mostly cloudy skies and lower diurnal fluctuations. Variation in outcomes increase starting Friday and are largely defined by the positioning/movement of Hurricane Helene remnants in conjunction with the west TN closed 500mb flow. Ensemble means suggest rain chances starting Friday morning south of Pittsburgh with the initial outer bands of the large area of low pressure. This assumes the surface low reaching the western NC/SC border Friday morning and lifting towards eastern KY by mid-day. Other higher-resolution model forecasts are slower and farther west with the low track, which favor the outer bands staying south of the region. Current forecast represents a blend of the two with higher/lower PoPs south of Pittsburgh possible in scenario 1/2, respectively. Low positioning will also influence surface gradient and the onset of SE wind increases (remaining well below advisory criteria). Confidence is high for slightly above average temperature continuing while cloud cover remains plentiful. && .LONG TERM /SATURDAY THROUGH TUESDAY/... KEY MESSAGES: - Rain chances will continue through the weekend, but no day looks like a washout. ------------------------------------------------------------------- Ensembles are in fairly good agreement in the broad idea of continued interaction between the TN closed low and Hurricane Helene remnants Saturday into Monday. The combined low area will be fairly stationary over the TN River Valley Saturday and slowly weaken before drifting SE into early next week. Expect periodic rain chances, abundant cloud cover, and above normal temperature during this period. Despite the agreement, large variations exist in the finer scale details of mesoscale banding, jet placement, and low positioning that will greatly determine timing/coverage/intensities of rain showers. Though any given period could see showers, the limitations of resolution for global models and general pattern recognition suggest dry conditions are more likely than not with smaller windows of rain that the forecast lends itself to. Ensemble means favor a northern stream trough kicking the sagging low out of the region by mid-week and ushering an airmass change. That said, scenarios remain on the sagging low staying farther south while ridging develops near the Great Lakes; this would foster drier and warmer than forecasted conditions. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... Scattered showers and thunderstorms will continue through this evening with the greatest potential for restrictions remaining north and northwest of PIT. Another large complex of rain can be seen on recent radar imagery over southern and central West Virginia gradually moving north towards the local area. This will bring another round of more widespread shower activity (similar to earlier this morning) during the late evening and overnight hours. Restrictions will continue throughout the period at FKL/DUJ, while other sites that have seen improvement this afternoon will once again see deteriorating conditions overnight with the onset of the the next round of rain. Most shower activity should move out of the area to the east by mid to late morning Thursday, with low cigs potentially lingering a bit longer before slow improvement occurs Thursday afternoon. .Outlook... Widespread restrictions will linger into Thursday before VFR is expected to end the week. Periodic rain chances are expected through the weekend. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...Cermak