Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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423 FXUS61 KCTP 241937 AFDCTP Area Forecast Discussion National Weather Service State College PA 337 PM EDT Tue Sep 24 2024 .SYNOPSIS... An amplifying upper level trough and slow moving frontal system will bring showery conditions to Central Pennsylvania through at least Wednesday, along with a few rumbles of thunder. As such, it will be cloudy and cool through midweek. The latter part of the week looks milder with at least partial sunshine expected into the weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Storms headed for SW at 19Z are organized into a little bow echo. They are approaching our fairly stable CWA. This usually helps keep the strong winds from mixing down. But, we`ll monitor closely mas SPC MRGL risk gets right up to Somerset Co. CAMs keep this bath of TSRA as the best/heaviest precip for the evening. The forcing passes through and into the central mtns, and deeper into the stable air overhead. Much of the overnight will be just cloudy and drizzly. However, more organized precip/showers move into the srn counties after 06Z and slide over the Lower Susq, mainly S of the Turnpike. Temps won`t move much (down maybe only 5-8F thru the entire night, again) and need little editing in the grids. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Upper ridging continues to pump up, more so to our east then overhead. The low pressure center associated with all this light rain will slide generally northward. This will mean a prolonged time of similar conditions. The moisture feed/PWAT gets a bit less favorable over the west, but stays in the 1.75" range in the SErn counties. Basin average QPF is less than half of an inch over all of the area, and many places will have less than a quarter of an inch across the short term period (Wed-Wed night). Again, little change to temps across the 24 hours. Will stick with continuity on temps. Sky cover pretty solid for most of the time on the deep SE flow. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Lingering showers across mainly E PA will continue into Thursday before a brief reprieve in rainfall. Shower chances will increase Thursday afternoon into the morning hours of Friday with the surface cold front lingering across southern Pennsylvania. The highest chances will mainly be confined south of the Turnpike; however, can`t rule out showers making it as far north as the northern tier Friday evening into Saturday morning with Chc PoPs across the Laurels throughout the day on Friday and into Saturday morning. There is still some uncertainty in regards to how Helene will impact central Pennsylvania, mainly dependent on interactions with an upper-level low stationed across the eastern Tennessee Valley. Deterministic model guidance has outlined that the bulk of rainfall will stay west of the area while a rather narrow, negatively tilted upper-level ridge holds strong from the Great Lakes through the Upper Ohio River Valley. Given the uncertainty with regards to upper-low interactions, did not deviate much from continuity and NBM guidance this cycle. The upper-level low and remnants of the tropical system will likely drift east across the Commonwealth early next week, bringing increased chances of shower activity into the beginning of next week, with highest chances generally across the western highlands. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... IFR/MVFR ceilings are expected to persist throughout much of the area for the 18Z TAF package with moderate-to-high (60-70%) confidence as SHRA/TSRA begin entering central Pennsylvania. Stable air will allow for the bulk of TSRA to decay as it continues to approach JST/AOO so have limited TSRA mentions throughout the near-term but have included borderline LIFR ceilings based on increasing moisture in the low-levels. Some localized drops towards 1SM will remain possible in the heaviest showers; however, generally lower confidence in timing/placement of the heaviest restrictions so have kept these mentions out of the 18Z TAF package. Further east, have kept mentions to MVFR at MDT w/ low-end VFR ceilings at LNS; however, generally expect ceilings to become lower in the 23-01Z period as SHRA edges slowly towards the airfield. Moving into the overnight period, moist low-levels will allow for a continuation of lower ceilings with IFR/LIFR conditions the most plausible solution at all airfields outside of the LSV airfields (MDT/LNS). As SHRA continues into the overnight at MDT/LNS, generally expect ceilings to continue into the 10-12Z Wednesday timeframe to trend lower w/ increased moisture. After sunrise, little improvement is expected throughout the daytime hours with model guidance indicating scattered SHRA. At this time, have trended closer to GLAMP guidance due to some remaining uncertainty that will need to be evaluated in future TAF packages. Outlook... Thu...AM low cigs/showers likely. Fri...SHRA increasing across S PA. Sat-Sun...Chance of low ceilings/SHRA. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...NPB AVIATION...NPB