Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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541 FXUS61 KCTP 162021 AFDCTP Area Forecast Discussion National Weather Service State College PA 421 PM EDT Mon Sep 16 2024 .SYNOPSIS... A ridge of high pressure at the surface and aloft will remain over PA today. 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 6 AM TUESDAY MORNING/... Upper level ridging extending from the Grt Lks to Southern New England will sustain fair weather across PA today. Warm advection aloft/upper level diffluence ahead of a low pressure system over the NC/SC coastline will spread a thin shield of cirrus north across PA today. Dewpoints have dropped into the 40s and even the 30s down into the Laurels as a batch of very dry air moved in with a wedge of subsidence associated with the high pressure system to our northeast. Valley fog will be possible again tonight, mainly 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 /6 AM TUESDAY MORNING THROUGH THURSDAY/... 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/... 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 /20Z MONDAY THROUGH SATURDAY/... Late afternoon update. Looking at just some high clouds across the area late this aft. Adjusted winds a bit in the TAF package. Earlier discussion below. VFR conditions prevail across central Pennsylvania with high (~90-100%) confidence that the main concern throughout the day will be gusts reaching upwards of 10-15kts across the Laurel Highlands (AOO/JST) this afternoon and early evening. Increasing mid-to-high level clouds are expected to enter southern Pennsylvania by evening and gradually expand northward with some thickening of the cloud deck as it progresses. The main concern for restrictions come near and after 06Z Tuesday as lower ceilings begin working into southern Pennsylvania. Some uncertainty on ceiling heights/timing bring about lower (~40%) confidence in the TAF throughout this period; however, expect LNS/MDT to dip towards MVFR thresholds generally in the 06-08Z timeframe and into the end of the TAF period with concerns for onset of IFR ceilings towards 09-11Z Tuesday timeframe. At this time, MVFR ceilings seem most likely at MDT/LNS (mentioned above) along with AOO/JST. There is lower confidence further north for UNV/IPT. 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 NEAR TERM...Fitzgerald/Colbert SHORT TERM...Fitzgerald/Colbert LONG TERM...Dangelo/Bauco AVIATION...Martin/NPB/Tyburski CLIMATE...NPB