Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 071756 AFDCTP Area Forecast Discussion National Weather Service State College PA 156 PM EDT Fri Aug 7 2020 .SYNOPSIS... Showers and thunderstorms are likely across most of central PA today. Locally heavy rainfall is possible with the greatest risk of flash flooding in the lower Susquehanna Valley. The overall coverage and probability of showers and storms will trend lower (drier) through the weekend with temperatures climbing 5 to 10 degrees above average into early next week. && .NEAR TERM /THROUGH TONIGHT/... Again, overall forecast is on track. FF threat has ramped up, esp for location e & n of State College. Major wave rounding the base of the upper trough is driving deep convection already this morning. That is usually a bad sign for Central PA. Heavy rain already fallen over the NE with the supercell that has tracked through from Lamar to nrn Schuylkill county has produced very heavy rain (and lots of wind damage). Interestingly, the damage from the supercell did not begin until the storm got to the spot where morning mixing and clearing had just begun minutes before. But, just that little bit of mixing likely allowed the strong wind down to the sfc. The low crud over the previous length of it`s path probably kept it elevated, despite all the parameters for svr. FF and svr threat (SE counties recently added to the MRGL risk for svr) should be waning as we go through the late afternoon and evening as this wave pushes to the east. Have padded mentions of svr and FFing for a few hours after that. Prev... Overall forecast remains on track. Current storm tracking along I-80 corridor has been persistent/strong and recently ramped its hail core to 1-2 inches. SPC may be adding a portion of the CWA to a MRGL risk with the 13Z update. Primary focus today will be on heavy rain/FF potential. WPC has upgraded the lower Susquehanna Valley to a SLGT risk ERO (level 2 out of 4). Several factors will contribute to heavy rain/FF threat in this area including but not limited to above normal moisture/PW, slow storm motions/cell training/mergers, and wet antecedent conditions. The dayshift should consider a short- fused FF watch if hires models remain bullish with +RA signal. Scattered to numerous afternoon/evening showers and storms should fade and shift eastward tonight into early Saturday morning. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... Increasing influence of high pressure sfc and aloft should spell a downward trend in diurnal convection to start the weekend. Pcpn probs derived from a blend of NBM and HREF are generally AOB 20% and focused across the eastern 1/2 to 1/3 of the CTP CWA. MaxT24hourChange will be about +2 to +6 degrees warmer vs. Friday. High confidence in dry conditions tomorrow night with mainly clear skies and light winds suggesting valley fog is possible into AM Sunday. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Fair weather should prevail on Sunday. The longer term will feature a return of warmer weather, with temperatures generally 5-10 degrees above average from Mon through Wed as an upper ridge builds over the Eastern US. Dewpoints climb back to the upper 60s and 70s for Tue and Wed, and perhaps even the mid 70s in the Lower Susq. Combined with temps in the upper 80s to near 90, this would mean Heat Index values take a run at the upper 90s to near 100 in the Lower Susq, so long as the low level moisture doesn`t mix out in the afternoon and cause the dewpoint to drop. Continued to knock down afternoon dewpoints from NBM guidance across central and northwestern zones Mon and Wed afternoon, where it looks like drier air will mix down. Weak forcing will favor isolated, pulse thunderstorms on Monday, mainly in the northwest. A cold front sagging south on Tuesday and Wednesday, combined with increasing humidity, should trigger more numerous showers and thunderstorms both days. Guidance seems to indicate the cold front may stall as it moves through PA, resulting in at least one more day of unsettled weather on Thursday. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... 18z update... Showers and thunderstorms will be most numerous this afternoon/early evening in the vicinity of KMDT and KLNS, where the most persistent restrictions are anticipated. Although showers/storms could briefly impact other central PA terminal sites, they would be short-lived if they occurred, with mostly VFR foreseen. Tonight, we anticipate widespread low stratus clouds and areas of fog to form, especially after 03-06z. IFR conditions are probable at all terminal sites for at least several hours. Saturday, low clouds and fog are expected to lift by 13-15z, with VFR thereafter. E-SE surface winds of 5-8 kt are expected this afternoon at KMDT and KLNS, with variable 5 kt or less elsewhere. Winds will be light overnight, then turn W-NW by midday Saturday at 5-8 kt. Outlook... Sun-Mon...Mainly VFR. Patchy low clouds and fog possible early in the morning. Tue-Wed...Increasing potential for showers and thunderstorms, along with associated restrictions. && .CTP WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through late tonight for PAZ019-027-028-036- 041-042-045-046-049>053-056>059-063>066. && $$ SYNOPSIS...Steinbugl NEAR TERM...Dangelo/Steinbugl SHORT TERM...DeVoir/Dangelo LONG TERM...Colbert/Banghoff AVIATION...Jurewicz

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