textproduct: State College

WHAT HAS CHANGED

* Winter weather advisory expanded to the Laurel Highlands and across the northern tier of central PA

* 925-850 mb wet bulb temps slightly below zero across the North-Central/ Endless Mtns of PA should favor an earlier onset/transition time to mainly wet snow this afternoon, first across the higher elevations AOA 2000 ft MSL, then working down in elevation early tonight. May need to collaborate/add in highly elevation dependent accums across this area for the 18Z Wed-00Z Thu period.

KEY MESSAGES

1) Rain to snow transition followed by gusty winds and plummeting temperatures will result in hazardous travel conditions over the Alleghenies later today into Thursday

2) Windy and much colder Thursday with lake effect snow showers tapering off Thursday night

3) Cold pattern shift stays locked-in through the upcoming weekend and with possible arctic blast into early next week

DISCUSSION

KEY MESSAGE 1...

Model guidance has trended slower and more amplified with the longwave trough carving out across the eastern CONUS. This lead to upward adjustments to snowfall totals into the 2-3/3-5" range, prompting an expansion of the winter wx advisory in the Laurel Highlands and across the northern tier.

A steady increase in large scale forcing/lift downstream of digging shortwave trough will promote a blossoming precip zone over CPA through the afternoon and evening. Hires model data indicates a rain to snow transition taking place between 1-7PM over the western and northern Alleghenies (earliest in the NW mtns). Strong 500mb height falls will work in tandem with an offshore jet streak to induce an intensifying sfc-850mb low tracking from CPA into eastern NY from 7PM tonight to 7AM Thursday. This low will drag an arctic front through the region overnight with temps plummeting behind a cold and blustery NW wind. The slower system evolution will allow for a slightly longer duration of deformation/upslope precip pivoting across the forecast area. The US220/I99 corridor marks a reasonable rain/snow transition line with rain being the more dominant ptype to the southeast of this line. As colder temps surge eastward late tonight, expect to see rain mix with or end as snow across the middle and lower Susquehanna Valley.

Single digit negative wind chills will great those heading out early Thursday morning across the western and central part of the forecast area.

KEY MESSAGE 2... Strong CAA and northwest flow behind the arctic front will support lake effect and upslope snow through the day on Thursday. Hires model runs continue to identify an upstream Huron connection that may lead to a couple robust snow bands or streamers. Additional lake effect snow accumulation is expected to the southeast of Lake Erie before snow showers gradually fade Thursday night.

Max temps will be 15 to 30 degrees colder Thursday (vs. Wednesday) with highs in the 15-30F range. The blustery wind chill factor will shave 15F from air temps making it feel like 0F to 15F.

KEY MESSAGE 3...

The mean 500mb trough re-loads with the next shortwave digging out of Saskatchewan into the Upper Midwest and Great Lakes Friday. Height falls and modest warm/moist advection could result in a round of snow pivoting into CPA Friday afternoon.

Reinforcing shortwaves within a broad cyclonic flow could bring additional periods of light snow/lake effect snow showers over the weekend into early next week.

A blast of bitterly cold arctic air may arrive on Tuesday with minimum wind chills entering the cold weather advisory range (-10 to -15F) over the western and northern mtns. Overall, the pattern next week will remain highly supportive of below average temperatures for mid January.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Rain showers crossing the region this afternoon are resulting in a steady lowering of both ceiling and visibility as the afternoon progresses. Conditions will first drop to MVFR then to IFR as a light rain falls ahead and along a cold front.

As the frontal boundary passes, all locations outside of the Lower Susquehanna Valley should transition to snow by 00Z. Conditions will drop to IFR in -SHSN over the higher elevation airfields of KJST and KBFD. Elsewhere...a drop to MVFR in scattered -SHSN. KLNS and KMDT likely won't see snow until after 00Z. A blustery west/northwest wind will develop and then continue Thursday with gusts in the 30 to 35 kt range, possibly even exceeding 40 kts at airfields across the southern half of PA late Thursday / Thursday evening.

Outlook...

Fri...Snow and IFR most likely over the NW airspace. Breezy with gusts from 180 degrees 15-25kt.

Sat/Sun...Light snow/IFR possible.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 1 AM EST Friday for PAZ004-005. Winter Weather Advisory from 5 PM this afternoon to 1 PM EST Thursday for PAZ006-037-042. Winter Weather Advisory from 5 PM this afternoon to 5 PM EST Thursday for PAZ024-033.