textproduct: State College

SYNOPSIS

* A quick-hitting system will bring a mix of rain and snow showers today with no impacts expected. * A brief period of lake effect snow will affect northwest PA tonight. * A more widespread/significant winter storm is expected Monday night and Tuesday.

NEAR TERM /THROUGH TONIGHT/

A cold front currently pushing through the Alleghenies will continue to drive a broken band of rain and snow showers across central PA. The better lift and instability will be over NW PA, where some pockets of moderate snow will be possible. While air temperatures have largely warmed above freezing, including into the low 40s across the Laurel Highlands, this cooler air in the wake of this front and wet-bulbing within the precipitation will put a halt to the "warmup". Will continue to monitor the northwest mountains, particularly along U.S. 6, for snow squall potential this afternoon ahead of the approaching front. Will also have to watch farther east into the Poconos where colder air has remained entrenched in the valleys there, but large scale forcing looks weaker that far east. Vertical thermodynamic profiles support more of a mix or all liquid rain farther south toward I-81 with a longer dry period and being farther ahead of the front. Max temps will be in the 40s south of I-80 and below 1500ft.

Gusty west winds will mix down behind the front, but speeds should max out in the 30-40 mph range on ridges. Lake effect snow will resume later this afternoon and continue overnight coincident with a secondary cold front pushing through and winds veering northwesterly. An additional inch or two of snow is possible in far northwest PA with light accumulations possible down toward I-80 in Clearfield County. Transient surface ridging bringing lowering inversion heights will bring and end to the precipitation by Monday morning.

SHORT TERM /MONDAY THROUGH TUESDAY/

Monday will be dry with high pressure arriving and centering overhead. Clouds will probably linger in the west with upslope flow before high clouds move in later in the day on Monday. High pressure should limit any real potential for additional lake- induced precipitation.

A more significant storm will approach the Mid-Atlantic on Tuesday as cold air in the middle of the country sets up a strong baroclinic zone over the eastern US. High pressure in the Plains should keep cold air in place on the northern side of the precipitation shield from a wave of low pressure progged to move out of the Gulf. This system should move northeast around the base of the aforementioned high pressure system, bringing increasing moisture to the Commonwealth Monday night into Tuesday.

The system at this time looks to be somewhat progressive with the lack of a strong area of high pressure to slow its forward momentum. Despite the expected quick forward movement, a deepening coastal low could still provide enough forcing juxtaposed with favorable upper jet dynamics to produce significant snowfall across the region. Snow looks to arrive later Monday night and lift across the region during the day on Tuesday. The eventual track and intensity of the low will have big implications on observed snowfall totals and the northward extent of any mix/rain scenarios.

The latest Winter Storm Outlook highlights a 30-50% chance of Warning criteria snowfall (6"+) in northeast PA, primarily east of US-15. GEFS and ECENS probabilities of 6"+ also support the 30-50% probability in the Poconos, with an even higher likelihood up through coastal New England. The ECENS suggests the higher terrain farther south could also bear watching. Have gone ahead and hoisted a Winter Storm Watch from Lycoming and Sullivan Counties down through Northumberland and Schuylkill Counties for Monday night into Tuesday evening. May certainly need to expand this and want to reiterate that storm intensity/track will weigh heavily on where future advisories and/or warnings may be needed. Regardless, a plowable snowfall is likely for almost all of central PA on the low end of the spectrum. Guidance has remained consistent overall for snowfall amounts with the last two runs, however some uncertainty remains whether or not warm nosing above the surface could limit snow across the PA/MD border into south central PA and the lower Susquehanna Valley. If mixing is a problem for anywhere in central PA, it would probably be for locations southeast of US-30 in York and Lancaster County. Continue to monitor the forecast in the days ahead, especially if you have plans to travel.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Precipitation moves east of the area by Tuesday evening, with perhaps a bit of lake effect or upslope snow into Wednesday morning. High pressure builds in Wednesday with a reinforcing cold front moving through Wednesday night into Thursday. This could produce some light snow across mainly the northern tier.

Thursday night and Friday look quite chilly, with lows in the single digits and teens while highs only make it into the 20s to low 30s. Otherwise, temperatures will be fairly consistent for the upcoming week and weekend, with highs in the 30s and lows in the teens and 20s.

By next weekend, another storm system looks to affect the Midwest and northeast US. Considerable uncertainty remains with the low track of this system. A track northwest of PA would lead to snow changing to a wintry mix and rain, while a track southeast of PA could look pretty similar to Tuesday's system with primarily snow. Regardless, a prolonged stretch of cooler than normal temperatures and an active storm track through the northeast looks to continue into the first week (and more) of December.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Current conditions show a mixture of high and low clouds taking up the airspace overhead. Light stratiform precipitation is present over central PA with minimal impacts to flight conditions present. The cold front is currently positioned over western PA, and it will progress eastward over the next few hours. There remains LLWS concerns for a time after the frontal passage, but winds will generally calm down after sundown tonight.

Cloud decks are a mixture of MVFR to VFR. Confidence is high in MVFR clouds hanging on in the western terminals of AOO, JST, and BFD, with some low probabilities of IFR at the higher terrain. Elsewhere, especially in the southeast at MDT and LNS, conditions should generally become VFR during the overnight tonight and early morning hours Monday.

Once precipitation clears later this afternoon, conditions should remain dry for tonight and Monday. The only site that could see some snow would be BFD as lake effect winds will bring snow banding potential into the northwest. The next widespread snowfall system will arrive on Tuesday as a coastal low develops and move up the coast of New England Tuesday afternoon.

Outlook...

Mon...Mixed/wintry precip likely early on. MVFR likely NW. IFR possible.

Tue...Snow possible, before a possible mix later in the day across the south. Restrictions possible.

Wed-Thu...Trending drier, lingering snow across NW PA.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Storm Watch from late Monday night through Tuesday evening for PAZ041-042-046-051>053-058.