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FXUS61 KCTP 031934 AFDCTP

Area Forecast Discussion National Weather Service State College PA 234 PM EST Sun Dec 3 2023

SYNOPSIS
Low pressure lifting passing just to the west of Pennsylvania today will drag a cold front across the commonwealth this evening. This will usher in a chillier airmass tonight into Monday, along with some light lake-effect and upslope rain and snow showers.

A weak clipper system will move through on Tuesday into Tuesday night. Temperatures will remain seasonably chilly before milder air begins to return toward the end of the week.

NEAR TERM /THROUGH TONIGHT/
The steady rain has pulled east of the area, with a few spotty rain showers lingering across northern PA. It is kind of a murky afternoon out there for much of central PA, although it is mild for December. Some breaks in the clouds are beginning to form across western Pennsylvania, however, and we'll have to keep an eye on this area for possible convective development this afternoon.

Strong shear exists over the area, thanks to a very strong 150+KT jet stream overhead, and any convection that develops could tap into the strong winds aloft. Any sfc-based CAPE that we can muster should be limited by the low December sun angle, but there could be just enough to help produce small hail and/or brief gusty winds in any storms that develop. SPC has painted a MRGL risk for svr wind/hail across the western highlands.

The quickly lowering sun should stifle any convection before it makes it very far to the east this evening. As the cold front pulls east of the area, a chillier airmass will begin to filter in overnight and we'll hold onto a 40-50% chc of rain/snow showers across the western highlands. The highest elevations could possibly see a light coating of snow by daybreak on Monday.

SHORT TERM /MONDAY THROUGH WEDNESDAY/
Monday will be chillier, with scattered rain/snow showers continuing across the northern and western highlands. Little in the way of snow accumulation is expected during the daylight hours.

Any lingering rain/snow showers across the highlands will dissipate Monday night, with lows dipping into the upper 20s to low 30s areawide.

By Tuesday, a weakening Alberta Clipper system will cross the Midwest and spread a shield of light rain/snow into western PA later in the day. Temperatures will likely be a bit too warm for much snow to accumulate during the daylight hours.

This system will quickly pass to our south Tuesday night. Light precip will continue and we could see some light snow accumulation (mainly over the western highlands) before the precip tapers off early Wed. Wednesday looks like a chilly day with a breezy NW wind developing behind the departing clipper.

LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/
Medium range guidance maintains a chance of snow showers on Wednesday with a slow to depart upper trough axis propogating east of the Commonwealth by Wednesday night, and an inverted sfc trough/weak clipper low passing south of the Mason Dixon line.
Northerly flow and upper level ridging builds over the region on Thursday maintaining fair and cool conditions before zonal flow pattern resumes late in the week.

Coldest conditions expected Wed/Thu before rebounding above climo levels by next Friday/Saturday. Might have to watch potential for some light overrunning precipitation along the NY border Thursday or Thursday night, if temps are still cold enough, that could result in light mixed precip. But for now consensus keeps most precip north of the PA/NY border.

Otherwise, rising 500mb heights ahead of organized storm over the west- central U.S. should also keep mild conditions into next weekend. GFS/ECMWF displaying their usual fast/slow bias with this system with CMC a middle ground with round of precip for later Sunday/Sunday night (very low confidence on timing).

AVIATION /20Z SUNDAY THROUGH FRIDAY/
IFR conditions remain widespread into this afternoon as warm front sluggishly lifts but buckles along the Allegheny Front.
Central and Eastern airfields should remain stuck with persistent lower cigs and vsbys (fluctuating between IFR and MVFR into this afternoon).

Brief improvement to MVFR conds spreading over the western Laurel Highlands (Cambria and Somerset) currently, and model soundings indicate 150-250+ J/kg of elevated MUCAPES propogate across the Alleghenies late this afternoon and evening. Cold front approaching this evening with aforementioned instability ahead of it will support scattered to numerous showers to last into the evening over the west and northwest. A few rumbles of thunder can't be ruled out with these showers over the Mtns of Western PA where the marginal destabilization occurs ahead of the cold front. LLWS also possible at the western TAF sites (KJST, KAOO, KUNV) into this evening as llvl inversion ~2k feet persists. The threat for LLWS may continue to expand and impact KIPT, KMDT and KLNS for up to several hours between 00-05Z Monday as the axis of the westerly low-level jet continues to move east.

Outlook...

Mon...MVFR/IFR western 1/3 with snow showers.

Tue-Wed...Light rain/snow with sub-VFR likely.

Thu...Chance of rain or snow.

CTP WATCHES/WARNINGS/ADVISORIES
None.

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