Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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221 FXUS61 KCTP 170613 AFDCTP Area Forecast Discussion National Weather Service State College PA 213 AM EDT Tue Sep 17 2024 .SYNOPSIS... An area of low pressure off of the South Carolina coast will lift north into Virginia by the middle of the week, before tracking east and off the coast by late week. An upper level ridge over the Great Lakes is likely to build into Pennsylvania by next weekend. && .NEAR TERM /UNTIL 8 AM THIS MORNING/... Added just a mention of a sprinkle or two over the Laurels later tonight/Wed AM as weak lift is progged as moisture increases. There are a few radar returns in ern WV, central VA at 02Z. But, the closest observation with precip is KLYH in srn VA. Otherwise, the current forecast is good with just some minor tweaks to T/Td. Prev... High clouds moving overhead are more opaque than transparent. Sky cover grids have been tweaked to increase them a bit more. Otherwise, SEG is diving to the botoom of the temp list without any wind. However, Td is still in the 50s and not expected to decrease much or at all overnight, so min temps look OK at this point. Valley fog will be possible again tonight in north central PA. Farther south, increased moisture and thicker cirrus aloft will inhibit radiative cooling enough to make fog less likely. For much of the Lower Susq valley, temps tonight are progged to be about 5 deg warmer than last, whereas 24 hr temp change in the northern tier is expected to be closer to 0. && .SHORT TERM /8 AM THIS MORNING THROUGH THURSDAY/... Latest runs of many models continue to keep it drier than earlier expectations for Tues-Wed. Dry air in place in low and mid levels. Drought begets drought. Have bumped PoPs down during the short term period using NBM (which also has the falling PoPs) as a basis. WPC MRGL EROs are now kept to our S, which seems very likely. Prev... Whether or not Potential Tropical Cyclone Eight organizes into a named system, the disturbance will track northwest to near Charlotte NC by late Tuesday. The bulk of latest guidance indicates the associated easterly low level jet and plume of Atlantic moisture linked to this system will weaken quickly as the disturbance moves north. However, it will come close enough to support a slight chance of showers over the southern tier counties late Tuesday. Any rainfall that reaches Southern PA Tuesday should be very light. Thickening cloud cover and an upsloping easterly flow should hold temperatures down Tuesday across the Laurel Highlands, where readings will likely not get out of the 60s. Elsewhere, model RH profiles support filtered sunshine through a veil of cirrus, with the brightest skies near the NY border. The best chance of showers across Central PA appears to come Wednesday, as the remnant low makes its closest pass to PA before shifting off of the East Coast late in the week. The bulk of recent guidance keeps the easterly low level jet and associated highest pwats just south of the Mason Dixon Line. The combination of increased moisture and large scale forcing ahead of the upper low currently targets areas just south of PA for locally heavy rain. Most likely rainfall by late Wed based on ensemble output ranges from <0.1 inch over Northern PA to around 0.5 inches over the southern tier. Recent dryness suggests the threat of flooding is low, even if a northward shift in the models brings the heavier rain into Southern PA. A 20-30 pct chance for rain continues into Thu, as various small low pressure centers attempt to take shape off the Mid Atl coast. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... 1030 PM Update holds minor changes for the late week and weekend. Only small/20 PoPs for the most part, and mainly for the SE. Prev... An upper level low over the region will keep clouds and showers around through most of the extended period. The best timing for showers remains unclear as this will be dependent upon the timing of multiple surface lows that will track near Central PA. Uncertainty begins to increase towards the weekend as there is quite a bit of spread in the guidance with respect to a building ridge to our west and how quick it pushes eastward. Ensembles suggest that the upper low will be slower to be replaced by ridging than had been shown over the past few days which will keep the chance for a few showers around through the weekend. Temperatures will generally be on a slight downward trend through the period with highs in the upper 60s and low 70s by Sunday and Monday. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... Lower ceilings across southern PA are being observed with MDT/LNS already down towards high-end MVFR restrictions as of 06Z Tuesday. Expect restrictions to continue at MDT/LNS through ~14Z with high (70-80%) confidence before lower-level clouds begin mixing out. Model guidance shows modest agreement with regards to lower clouds making their way into AOO/JST near 08Z with lower-level clouds continuing to bring MVFR restrictions through 18Z Tuesday. GLAMP guidance has been persistent with regards to IFR thresholds being met at JST, and given higher probabilities of IFR conditions in the 10-12Z timeframe have continued to outline these conditions with moderate (~60%) confidence in this timeframe. Uncertainty remains with northward progression of the lower-level cloud deck brining MVFR conditions to UNV/IPT so have outlined SCT lower-level clouds with a brief period of MVFR conditions at UNV near sunrise. In the 18Z Tuesday timeframe through the end of the TAF period, VFR conditions are expected with moderate-to-high confidence (50-70%). Some lower-level clouds could begin pushing their way into the southern airfields (JST/AOO/MDT/LNS); however, the best chances for restrictions come after 06Z Wednesday so have opted to keep mentions of scattered low-level clouds at this time. Outlook... Wed...SHRA w/ Isolated PM TSRA, highest chances across SE PA. Thu-Fri...Lingering showers possible, mainly across the east and south. Sat...Mainly dry conditions. && .CLIMATE... The first day of Autumn 2024 (Fall Equinox) begins at 8:44 am EDT on September 22nd. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Fitzgerald/Dangelo NEAR TERM...Dangelo SHORT TERM...Fitzgerald/Dangelo/Colbert LONG TERM...Dangelo/Bauco AVIATION...NPB CLIMATE...NPB