textproduct: State College

SYNOPSIS

* Snow and embedded squalls will develop tonight across parts of central PA, associated with a strong cold front * Areas of lake enhanced and upslope snow will persist into New Year's Day, along with very cold wind chills * Moderating temperatures are expected over the weekend and into next week

NEAR TERM /THROUGH THURSDAY/

As of mid-afternoon, we're in a relative lull across central and northwest PA, as backing flow ahead of our next incoming disturbance shunts the main Lake Erie band well north, and also effectively cuts off Lake Erie moisture to help feed lake- enhanced/upslope snow showers into the Alleghenies.

However, the break won't last long, as a digging short-wave over the northern lakes and an associated surface arctic boundary is waiting in the wings. Model guidance depicts increased westerly flow in the 925-850 mb layer this evening as these systems approach, which will enhance the upslope component into the Laurel Highlands, in addition to the general synoptic lift at play from the upper-level wave. This all points to a period of moderate-heavy snow tonight in the Laurel Highlands, with HREF guidance showing increased probabilities for 1"/hour rates between about 02z and 09z. Thus, our current Winter Storm Warning in Somerset county and high-end Advisory in Cambria county appear to be in good shape.

The other issue later tonight will be snow squall potential along the surface boundary. Good convergence along this front, unstable conditions in the upper part of the boundary layer, and decent forcing aloft point to the potential for robust linear development. We'll continue to message this threat and closely monitor conditions tonight, especially considering NYE celebrations concurrent with likely snow squall development.

NW flow lake-effect bands are also expected to kick in overnight behind the front. This scenario is well handled by our Warning in Warren and McKean counties, as well as adjacent Advisories for Potter, Elk, Cameron, and Clearfield counties.

On New Year's Day, strong cold advection and moisture off Lake Erie will continue the lake snow bands at least through the midday hours, with a gradual reduction likely in the afternoon, as the capping inversion starts to come down.

As for the snow in the Laurels is concerned, although NW flow upslope will continue to produce general snow showers, the heaviest snow should be over, as synoptic-scale upglide will be significantly less by then.

In general, it will be a cold and windy start to 2026, with -/+ single digit wind chills anticipated for most of the area.

SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/

Cold NW flow will continue this period, with brisk conditions and biting wind chills foreseen area-wide.

Although most of central PA will either be dry or just experience a few flurries, lingering lake snow bands in the northwest snow belt areas, as well as upslope snow showers in the Laurels, could bring small additional accumulations.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

In general, a break from the persistent cold/below normal temperatures is foreseen for central and northwest PA, as upper-level heights relax, and a more zonal flow regime settles in.

Fast moving disturbances could bring occasional periods of light rain or snow, but overall, no major storms are anticipated at this time.

AVIATION /00Z THURSDAY THROUGH MONDAY/

For the 00Z TAF package, minor timing differences. Main change was lower CIGS with TEMPO 1/4SM groups, given wind and low visibility fcst. Also a bit more with wind speeds later tonight into Thursday. Happy New Year to all.

Late afternoon update.

Adjusted TAFS some. Some spots with low CIGS, but not much in the way of snow showers for a brief time, much of the hazy look is not snow, but just moisture, fog and smoke.

Earlier discussion below.

Lake effect SHSN have lifted away from the western highlands, but a patch of very light but nearly-constant snow is falling at 18Z. This light snow should diminish/end for a short time, but will be replaced rather quickly by another, larger patch of more-constant, light snow which should move into the west before 23Z. That patch is being forced by a significant short wave trough aloft. Expect conditions to deteriorate again as that snow becomes widespread. While this is going on, the VFR over the eastern terminals will continue.

Things get worse for travel this evening and tonight. The trough aloft will be undercut and the snow enhanced by a very sharp and active arctic front. The front will force at least one line of snow squalls. Some model guidance has the squall as one, continuous/coherent line/band right along the front. Meanwhile, some guidance has multiple/broken bands. Each of these scenarios would still push squalls into the southern terminals. However, we do expect the strength of the squalls to decrease as the front passes an RVL-SEG-AOO line. Some re-intensification of the squalls is still possible (30%) in the Lower Susq (MDT/LNS), though, as their slightly warmer temperatures there as the front arrives could cause some CAPE/instability. But, guidance probability of IFR cigs/visby drops to <20% after the front pushes thru IPT-UNV-JST. Gusty WNW wind will accompany the squall(s) with the highest gusts over the Laurel Highlands.

Timing of the worst of the squalls (or single squall) is looking a little slower than previous guidance. We are now well within the CAM/HREF's time-horizon of best performance. Encouraging is that many of them have started to agree on a consensus of timing. Therefore, with some increased confidence in the time of arrival, we have adjusted the times when LIFR is possible at each terminal back/slower 1 to 3 hours from what was mentioned in the 12Z package.

Post-FROPA, the sfc wind will go westerly W, and may even decrease a few KTs on the whole with less gustiness. But, the arrival of daylight and mixing will get them gusty again. but still be gusty. The SHSN over the Laurels (JST) will be only widely sct after 12Z. The classic lake effect wind field will keep BFD under the threat (>60% chc) of IFR all Thurs and even Thursday night - even though SHSN will taper off in BFD aft 00Z Fri.

Outlook...

Fri...VFR S & E. MVFR cigs with a chance of a snow shower at BFD and perhaps JST.

Sat...Still a chance of a snow shower early at BFD, then VFR.

Sun...Mainly VFR.

Mon...Clipper system with sct/numerous SHSN W w/IFR poss. Mainly MVFR E.

CTP WATCHES/WARNINGS/ADVISORIES

Lake Effect Snow Warning until 7 PM EST Thursday for PAZ004- 005. Winter Weather Advisory until 4 PM EST Thursday for PAZ006-010- 011. Winter Weather Advisory until 10 AM EST Thursday for PAZ017- 024. Winter Storm Warning until 10 AM EST Thursday for PAZ033.