textproduct: State College

SYNOPSIS

* Breezy early today with sun and clouds; dry for holiday travel * Impactful post-Christmas snow and ice Friday and Friday night * Another round of mixed precip Sunday then sharply colder with blustery winds and lake effect snow to start next week

NEAR TERM /THROUGH TONIGHT/

Breezy start to Christmas Eve with partly to mostly cloudy skies. High pressure migrates over CPA this afternoon providing a dry day for holiday travel.

Clouds increase tonight in response to low amplitude shortwave diving southeast from southern Lake Michigan into the Central Appalachians. Hires model data continues to indicate the potential for spotty/light mixed precip to reach the forecast area in the 06-12Z Thu timeframe. Highest odds/POPs are focused over the western and southern periphery of the CWA with dominant ptypes either light rain/drizzle or freezing rain/drizzle.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/

The weather looks largely benign for the rest of Christmas Day with cloudy skies, WNW breeze and max temps +5-10F above the historical average. High pressure ridge drifts over CPA Thursday night bringing some clearing and colder min temps in the 15-25F range. The sfc ridge and cold air wedge channels down the east side of the Appalachians by Friday morning - setting the stage for a classic CAD "overrunning" post-Christmas wintry mix event.

Strong warm air advection, isentropic lift, and healthy mid-to- upper level ascent (ahead of sfc low tracking from IA/IL border eastward to western PA btwn 12-24Z Friday) will send anomalous moisture plume into a cold and dry boundary layer (sub-freezing wet bulb temperatures at the surface). This will allow for an icy mix of sleet/freezing rain over the southwest 1/3 of the CWA. The best ice signal >0.25" is over the Laurel Highlands. Farther to the northeast where cold layer is gradually deeper, snow/sleet/zr transition is forecast. A deep cold layer below the elevated warm nose could favor the majority of precip falling as sleet over the interior central ridge and valley region where WPC WWD shows a broad area of 0.50"+ of sleet accumulation. Precip should stay snow the longest over the northeast periphery of the CWA with perhaps up to 4-6" in the eastern portions of Tioga/Sullivan/Columbia/Schuylkill Cos.

There remains ongoing fluctuations in the forecast track which could result in additional changes to which areas see the most snow and ice. That being said, we have high confidence in an impactful post-Christmas winter wx event. We issued a winter storm watch for the entire CWA with an emphasis on hazardous travel impacts; the best odds (highest confidence) to reach warning criteria are over the Laurels due to significant ice accretion with WSSI-P showing >50% odds for minor impacts over the remainder of the CWA.

LONG TERM /SATURDAY THROUGH TUESDAY/

Some spotty freezing drizzle/drizzle could linger into Saturday morning with low clouds trapped under inversion. The weekend warmup has been tempered due to persistent low clouds Saturday and rainfall now projected on Sunday. If precip arrives early Sunday, there is a chance it could be freezing rain. Periods of rain are expected Sunday afternoon into Sunday evening before a sharp arctic cold front plows southeastward across the region Sunday night. An arctic blast is now forecast for early next week with strong gusty winds, lake effect snow and +/- single digit wind chills.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

High pressure building into the area will bring a decent conditions this afternoon with decreasing winds.

Later tonight, some lower clouds with patchy light rain move toward southwest PA, but expect JST to be just on the edge of this, so left rain out.

As the system passing to the south and west of our area moves out Thursday morning, winds will shift more to the northwest and becoming gusty. Some lower clouds will be possible at BFD and JST, as winds shift to the northwest.

For Friday, warm advection will bring the potential for snow, sleet, and freezing rain to central PA. Some impovement for Saturday, but a strong cold front on Sunday will bring more adverse weather to the area.

Outlook...

Fri...Snow developing, then a mix of sleet and freezing rain.

Sat...Spotty precipitation tapering off.

Sun...Rain with -FZRA possible across higher elevations early, then becoming windy. Restrictions possible.

Mon...Windy and colder with snow showers across the mountains.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Storm Watch from Friday morning through Saturday morning for PAZ004>006-010>012-017>019-024>028-033>037-041-042- 045-046-049>053-056>059-063>066.