Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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331 FXUS61 KCTP 240451 AFDCTP Area Forecast Discussion National Weather Service State College PA 1251 AM 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 late this week and into the weekend. && .NEAR TERM /UNTIL 8 AM THIS MORNING/... A moist llvl easterly flow will continue to sock in widespread stratus and ridge-shrouding fog overnight through the mid morning hours Tuesday across the bulk of the CWA east of the Alleghenies. A Dense Fog Advisory continues for Schuylkill Cty through 12Z Tues, focused on the I-81 corridor that runs along the highest terrain of the county and experiences the greatest, orthogonal upslope component to the wind in this setup. Vsbys in some places along the stretch of I-81 from near Delano to Hegins will be near zero. Otherwise, look for generally scattered showers and areas of drizzle amounting to less than 0.10 of an inch overnight as a deep layer of mid level dry air spreads east over the aforementioned moist low-level environment. Temps will only fall by 1-3 deg F overnight, given the current 0-3 deg F T/Td spread. Lows will be between 55 and 60F. && .SHORT TERM /8 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... Tuesday/Tues night will feature several weakly coupled jet segments lifting NE across the CWA, accompanied by an anomalous southerly LLJ of around +2 sigma. Good surge of moisture (PWAT of 1.4-1.7 inches) and forcing comes across the CWA in the afternoon and evening Tuesday. Some instability will be present in the west, so the slight chc T will be retained there. SPC even touches Somerset Co with a MRGL risk of svr wx. Similarly, the ERO is also a MRGL risk - and only in Somerset Co. The showers/thunder should really not be enough to drop enough rainfall to generate flooding there since it has been so dry. The rain today (Mon) was barely enough to get water to the soils. Maxes will be just 5--8F above nighttime lows. Any breaks in the clouds in the AM will close up. Tues night is mainly rain, Basin averages thru the next 36 hrs will vary between 0.25-1", and will be a welcome rainfall in many areas. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Model guidance outlines another surface low-pressure system tracking northeastward across the Great Lakes and into southern Ontario on Wednesday, with slightly more moisture and lift available as the warm front aligns itself north-to- south across west-central PA. Given slightly better lift with this low- pressure system overhead coupled with enhanced moisture, have retained likely PoPs on Wednesday with highest chances during the late morning to early afternoon hours. Heavy rainfall threats look less robust compared to previous forecast cycles; however, some instability will allow for thunderstorms across the Laurels, brining some potential for locally heavy rainfall, with maximum totals ~0.50" on Wed. Lingering showers across mainly E PA will continue into Thursday before a brief reprieve in rainfall Thursday evening and into Friday morning. Rainfall chances begin to increase as Friday morning progresses with the potential remnants of PTC9 approaching the area. There is still some uncertainty in regards to how PTC9 will impact central Pennsylvania, mainly dependent on interactions with a trough stationed across the eastern Tennessee Valley. At this time, deterministic and EFS model guidance shows modest agreement in the bulk of rainfall keeping south/west of the area while a rather narrow, neg tilt upper ridge holds strong from the Great Lakes through the Upper Ohio River Valley and Carolina Coast. Given the still existing uncertainty, did not deviate much from continuity and NBM guidance once again this model cycle. If precipitation manages to make way into central Pennsylvania in the Friday- Sunday timeframe, highest chances (25-35%) will be across S/W PA along the Laurels with a SChc (15-25%) progged west of the Susquehanna Valley. It looks like enough low-mid level ridging will maintain a deep layer of dry air across the NE 1/3 to 1/2 of PA to keep precip chcs minimal there through the weekend. Upper low and remnants of the tropical system will likely drift east across the Commonwealth early next week with a fairly good chc for showers. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... For the late evening update and the 06Z TAF package, I added a bit more detail. Overall looking at low CIGS today into tonight, given a southeast flow of cool, moist air. CIGS may be a bit higher at MDT and LNS at times, but expect a lot of variation. Any improvement with CIGS today, will be short lived, as day light is shorter now, thus expect CIGS to come back down toward sunset. Visibilities not bad as of Midnight. The visibility may drop some when showers become more widespread today, but dewpoints not fcst to come up much, so time of day may offset the effects rain become more widespread. Outlook... Wed...Low cigs/showers likely. Improving conditions possible W Mtns Wed PM. Thu...AM low cigs/showers likely. Fri...No sig wx expected. Sat...Chance of low cigs/rain Laurel Highlands. && .CTP WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 8 AM EDT this morning for PAZ058. && $$ SYNOPSIS...Lambert/Dangelo NEAR TERM...Lambert/Dangelo SHORT TERM...Lambert/Dangelo LONG TERM...Lambert/NPB AVIATION...Fitzgerald/Martin