textproduct: State College

WHAT HAS CHANGED

* Increased snowfall totals over northwest PA with lake effect snow Wednesday afternoon through Thursday night. Totals were increased very slightly from earlier shifts. * Winter Weather Advisory issued for Warren County from 11 am Wednesday through 1 AM Friday. Briefing sent.

KEY MESSAGES

1) Mild on Wednesday, but much colder by sunrise on Thursday.

2) Low pressure tracking just to the north and west of the area should bring some elevation wet snow and valley rain across much of the area Wednesday into early Thursday, turning to snow in the valleys from northwest to southeast Wednesday night and early Thursday with a possible flash freeze of wet or slushy surfaces. Cold temps Thursday keeps the precip all snow.

3) Active weather continues through the weekend and into the beginning of next week with multiple chances for snow. Turning colder by Tuesday.

DISCUSSION

KEY MESSAGE 1...

Watching radar and obs for precipitation. Most of the rain is not reaching the ground. Earlier info. below.

Warm advection with a minor wave aloft tonight will keep temps mild (over freezing everywhere but parts of northern PA). Without much moisture to work with and low PoPs, we'll not have much worry for p-type tonight with a few rain or wet snow moving across the northern mtns. Maxes will be in the upper 40s over the SE on Wed. Cooler to the north and west, but mainly above freezing prior late afternoon on Wednesday across the NW.

KEY MESSAGE 2... Temperatures falling Wednesday night a concern, but normally the wind helps dry the sfc off, after being wet. Will continue to look over this situation. Earlier information below.

A sharp cold front moving through the western part of the state late Wed and across Central and Eastern PA Wed night interacts with fairly limited moisture. The forcing isn't focused until mid-day Wed, first over the west as deepening uvvel associated with the thermally direct branch/right entrance region of a 130 kt upper level jet slides overhead.

Temps should stay plenty mild for the SErn half of the area to be rain Wed/Wed evening. Temps over the NW have trended slightly cooler and may even support a mix of rain and snow at the onset of precipitation before changing completely to snow by late afternoon. As temps get colder Wed evening/night, the lingering precip in the east should turn to snow as it ends. Major models all have precip ending (well) before sunrise Thurs in the central and eastern zones.

Northwest flow behind the front will support lake effect and upslope snow through the day on Thursday. Recent model runs are beginning to show a Lake Huron connection developing, resulting in slightly higher expected snowfall amounts downwind of Lake Erie. We have issued a Winter Weather Advisory for Warren County where 2 to 4 inches of snow is expected, with locally higher amounts possible across the northwestern third of the county. While the wind direction will be favorable for upslope snow showers in the Laurel Highlands, model soundings suggest that moisture in the DGZ will be limited. Snowfall amounts for much of Cambria and Somerset counties will likely be less than 2 inches, though slightly higher amounts are possible on the western ridges of Somerset County.

KEY MESSAGE 3...

Moderate uncertainty exists in the pattern for Sat-Sun, mainly in the timing of a series of waves from the west. Long wave trough moving across the nrn plains and Great Lakes will drive the bus. But, the details are tough to pinpoint at this range.

A burst of arctic air is possible and best timing on that right now would be Sat night or Sun. SNSQs possible as that would move through with a sharp/quick/deep drop in temps. Wind chills could also near Cold Weather Advisory criteria.

Even colder temperatures possible by next Tuesday.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

High confidence in widespread VFR through the first half of this evening. LLWS expected to continue for the next few hours with the sheer exceeding 45kts for most terminals. We should see this threat subside overnight as winds within 2000 feet of the deck diminish.

Expect lowering/deteriorating ceilings Wednesday as light rain mixes with and changes to snow Wednesday night. Confidence is increasing in widespread ceiling and visibility reductions. The earliest impacts should occur overnight at BFD around 09Z as precipitation begins in the northwest. Deteriorating conditions will trend towards the southeast throughout the day on Wednesday. Everywhere outside of the Lower Susquehanna Valley should transition to snow by 00Z Thursday. LNS and MDT likely won't see snow until after 00Z. A blustery west/northwest wind will ensue for Thursday.

Outlook...

Thu...MVFR/IFR snow showers persisting across the western and northern airspace; windy with sfc gusts 25-35kt from 280-310. Winds decrease Thursday night.

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 from 11 AM Wednesday to 1 AM EST Friday for PAZ004.