Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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413 FXUS61 KCTP 260538 AFDCTP Area Forecast Discussion National Weather Service State College PA 138 AM EDT Wed Jun 26 2024 .SYNOPSIS... A cold front will push southeast across the region Wednesday night, followed by high pressure building in Thursday and Friday. A relatively zonal flow will remain in place through early next week, with a cold front passage either late Saturday or early Sunday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Late evening water vapor loop shows a potent shortwave tracking well north of PA through the St Lawrence Valley. Satellite loop at 03Z shows cumulus with decent vertical development along the trailing low level jet from Northwest PA through the southern tier of NY state. Warm advection along this feature could potentially produce a shower/tsra across the N Mtns late this evening. Otherwise, tonight looks quiet with varying amounts of mid and high level cloudiness overspreading the state ahead of an upstream trough over the Plains. An active southwest breeze will draw steadily rising dewpoints into the region tonight, resulting in much warmer conditions than last night. See no reason to deviate from NBM mintemp, which range from the mid 60s over the NW Mtns, to the low 70s in the Lower Susq Valley. && .SHORT TERM /6 AM THIS MORNING THROUGH FRIDAY NIGHT/... Diurnal heating of an increasingly moist/unstable airmass, combined with falling heights ahead of the upstream trough, will result in developing convection during Wed afternoon. A ribbon of relatively strong mid level winds of 40-50kts, combined with progged moderate instability across Central and Southern PA, suggests organized convection and locally severe weather can be expected across this part of the state Wed PM. Some of the latest model guidance suggests an eastward-moving MCV could result in a batch of strong-severe convection across Southern PA in the 16Z-21Z time-frame, with diminished potential in the rain-cooled air behind it. However, wouldn`t place too much weight on this right now, as the strongest shear should be in the late afternoon to early evening timeframe. Some of the 12Z HREF members indicate UH values >150 across Southern PA in the early evening, which is supportive of supercells. Latest ensemble plumes indicates most likely aerial average rainfall Wed PM will be around a half inch. However, isolated amounts around 2 inches appear likely based on the latest HREF and a combination of moderate instability and +1-2SD pwats. Thicker clouds will likely cap temps to the upper 70s across the NW Mtns Wed, while a decent amount of sun is anticipated across the southeast counties based on model RH profiles. 850mb temps support highs as warm as the low 90s across the Lower Susq Valley. The combination of heat and humidity should result in heat indices peaking in the mid 90s in that part of the state. Dwindling convection from northwest to southeast is anticipated Wed night, as the upper trough and associated cold front work through. Large scale subsidence and the arrival of much drier air behind the exiting cold front should then result in fair and seasonable conditions Thursday. Surface high pressure building over the region should result in fair and cool weather Thu night. Fair and slightly warmer conditions are likely Friday, as low pwats persist over PA and a return southerly flow develops as the surface high passes off the coast. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Latest medium range guidance is showing an unusual lack of spread among its members, all of which track a surface low north of PA Saturday, with a trailing cold front coming through Sat night into early Sunday. The lack of spread with regards to timing of the front, combined with progged GEFS pwats of +2-3SD, supports an increasing confidence in showers/tsra Saturday. A leading warm front could produce showers/tsra as early as Friday night and a slowing cold front could cause convection to linger into Sunday, mainly over the southeast counties. However, ensemble plumes indicate the most widespread convection should occur Sat afternoon and evening. There is some potential for severe wx Saturday PM, as decent mid level flow overspreads an increasingly moist warm sector. Ensemble plumes currently indicate moderate capes in the 1000 J/kg range and model 0-6km shear is in the 35-40kt range. If the cold front slows enough, severe wx would also be possible across the eastern edge of the forecast area Sunday PM. Latest EPS and GEFS both support fair weather with near to slightly below normal temps and low humidity early next week associated with high pressure building east from the Grt Lks. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... VFR conditions are being observed across all of Central PA as of 05Z, but all guidance suggests that MVFR ceilings will develop across the northwest by 09Z. These low clouds should dissipate by mid morning and a period of VFR is expected area-wide through at least the early afternoon. Uncertainty begins to increase throughout the afternoon as there are still questions about the timing of showers and thunderstorms moving in ahead of a cold front. Showers are likely to begin kicking up around 18Z in western PA before overspreading to the east and strengthening through the afternoon. A few of these storms could be strong to severe with any impacted TAF site likely to see high wind gusts and briefly lowered visibility. The best chance for strong storms will be between 18Z Wednesday and 03Z Thursday. Have added broad periods of VCTS at each TAF site, but this timing will have to be refined with further forecast updates. As the showers and thunderstorms exit to the east during the late evening, guidance indicates the potential for low clouds to stick around across a large portion of the area. The HREF shows the highest probabilities of IFR ceilings (50-60%) at BFD and JST, with lower probabilities of MVFR ceilings at all other sites except MDT and LNS. Outlook... Thu-Fri...Generally VFR. Sat-Sun...Thunderstorm impacts possible. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Fitzgerald NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald LONG TERM...Fitzgerald AVIATION...Bauco/Bowen