textproduct: State College

WHAT HAS CHANGED

*No significant changes

KEY MESSAGES

1) Potential for the first accumulating snowfall of the season, especially across the Laurels and the northern tier of Pennsylvania.

2) Northwesterly flow bring much cooler temperatures this weekend, with lake-enhanced snow showers.

DISCUSSION

KEY MESSAGE 1: Potential for the first accumulating snowfall of the season, especially across the Laurels and the northern tier of Pennsylvania.

The main game in town across central Pennsylvania over the next week will be the potential for the first accumulating snowfall across portions of central Pennsylvania. As a low pressure system approaches the region from the Mid-Ohio Valley late Wednesday into Thursday, precipitation chances will begin to ramp up throughout the overnight period. A slightly warmer trend has been observed since this time yesterday, with virtually all of the GEFS ensemble members outline temperatures above the freezing mark across NW PA (where temperatures will be the coolest) throughout the daytime hours on Thursday, thus there is higher confidence on outright rain. Given that this trend also extends into ENS guidance, fairly confident on there being no snow through sunset on Thursday.

Diving into the details after sunset Thursday evening, ensemble guidance begins to show much more spread with respect to temperatures, especially in GEFS guidance. All guidance continues to agree on a drop in 850mb temperatures from +4C to +5C ahead of this colder air trending closer to -4 to -5C by Friday morning/afternoon. This colder air will bring increased chances for a transition to rain/snow showers before an outright transition to snow showers for areas north/west of the I-80/I-99 corridor by sunrise on Friday. In terms of snowfall forecast (only goes through Friday afternoon), have increased snowfall accumulations across the highest elevations of Somerset County given NBM model guidance tends to verify closer to the 90th percentile. This puts highest accumulations at this time between 1-2" there while much of the rest of the area trends below the 1" mark. Further south/east, temperatures will be marginal with rain/snow mix possible in the highest elevations and cannot completely rule out some wet snowflakes flying Friday morning however, confidence remains low in any accumulations. Newest WSSI guidance does outline "Winter Weather Conditions" across portions of central Pennsylvania (mainly north/west), so folks should be prepared for the potential of wintry weather for their Friday morning commute and should be prepared to drive carefully given these conditions.

KEY MESSAGE 2: Northwesterly flow bring much cooler temperatures this weekend, with lake-enhanced snow showers.

Cooler temperatures and breezy northwesterly winds will take hold of the region as the area of low pressure shifts east towards the New England Coast. Recent medium-range guidance indicates the area of low pressure beginning to deepen, allowing for a tightening pressure gradient across the region. This will mark a return of breezy conditions and much cooler than average temperatures for the middle of November. At this time, breeziest winds appear to be across the highest elevations along the Allegheny Front with a secondary areas across southeastern Pennsylvania. Some of the more recent guidance suggests maximum wind gusts exceeding 25 mph across the board on Saturday with the aforementioned areas pushing closer to the 30 to 35 mph range. A slight uptick in winds continues into Sunday, with 30-35 mph winds across all of central Pennsylvania with isolated wind gusts upwards of 40-45 mph across the higher elevations of the Laurel Highlands.

This northwesterly flow will bring a continued chance for precipitation as flow across the Great Lakes becomes more favorable for lake enhanced snow showers. There still remains some uncertainty with respect to wind direction (will there be too much of a northerly or westerly component) so have continued to role with NBM model guidance in the Friday to Saturday timeframe but could see some refinement in future forecast packages. Chances for precipitation begin to decrease on Sunday and into the first half of the week as synoptic setup becomes less favorable for lingering showers. A slight warming trend emerges into the beginning of next week, with temperatures trending closer to climatological averages by Tuesday.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Update - for the Overnight:

KCCX Radar showing some slightly enhanced inbound velocities drifting SE of a line from KDUJ to KELM over the past 30 minutes, likely depicting some ducting of the beam within the shallow, cool airmass behind a very weak cold front.

This boundary may move another 30-50NM further SE overnight. only a very subtle wind shift to the WNW by 10-20 deg is expected in the wake of the frontal passage.

The main impact we'll see will be the formation of some IFR to LIFR stratus later tonight through early Wed across the NW Mtns (KBFD) where milder air aloft and a slight uptick in Theta-E will drift in from the SW - overrunning this shallow cooler airmass.

The wind should go light for most places overnight as high pressure moves in. There is a 50% chc that fog forms in some of the river valleys tonight. We did not go IFR anywhere due to fog at this point, but do mention VCTY FG at several sites. BFD is the only terminal that is more than likely (90%) to go IFR as low clouds move down from the N. These low clouds may get as far SE as IPT/UNV, but there's only a 30% chc of that.

The low clouds in the N should break up a few hrs after sunrise. Sct VFR cu or altostratus will then lift northward into PA after noon concurrent with high clouds increasing from the N. Low pressure approaches quickly from the W with the storm maturing rapidly, too.

Conditions gradually deteriorate to IFR over the west first on Wed night, with -RA spreading across about half the state by sunrise Thurs. LIFR clouds are possible in the N/W Thursday and some snow may mix in to BFD and JST by sunset. BR/FG also expected in many places as the clouds and precip become widespread but light Thurs. The occluded sfc low will likely jump to the E later in the day, but the passage will veer the wind to the SW then NW before the end of the day. LLJet seems not strong enough or low enough to mention any LLWS. any showers left Thurs night and Fri will be -SHSN in BFD and JST. UNV, AOO, IPT may see some flakes mix in, but not last more than an hour at a time (showery).

Outlook...

Fri PM...-SHSN, ocnl IFR NW. -SHRA, MVFR SE. Gusty NW wind.

Sat...Improving, but still gusty with MVFR clouds and isold -SHSN for BFD/JST. VFR elsewhere.

Sun...VFR, gusts NW 15-25KT.

CTP WATCHES/WARNINGS/ADVISORIES

None.