textproduct: State College

SYNOPSIS

* Dry and cloudy weather today * Rain showers overspread the northern tier on Sunday; some icing possible in NE PA with subfreezing surface temperatures * Increasingly mild into Monday morning before a cold front slams through and brings lake effect snow showers, strong winds, and sharply colder temps/wind chills Monday night into the New Year.

NEAR TERM /THROUGH SUNDAY/

KEY MESSAGES: - Dry conditions and a slight rebound in temperatures for today, but untreated and elevated surfaces will continue to be slick. - Degree of clearing tonight and resultant low temperatures Sunday morning could enhance the risk of freezing rain Sunday afternoon. -----------------------------------------------------------

Areas of weak high pressure near Chicago and over Southern Ontario will consolidate and drift east across the region tonight. Subsidence from approaching high pressure has been ineffective at eroding stubborn clouds across PA so far, and it seems that trend will continue for most of the region into the evening. Best chance for some breaks will be east of the Susquehanna River south of I-80.

Highs still on pace to remain below freezing for most locations north of I-80. The South Central Mtns and Lower Susquehanna Valley will see the mercury climb to between 35 and 40F. It's a good idea to get outside and shovel or clean off vehicles this afternoon if you see temperatures rise above freezing at your location. Temperatures will fall off again tonight, dropping into the upper teens in the northeast and staying near freezing in the southwest. If there is more clearing than expected overnight, lower temperatures on Sunday morning could lead to an increased risk for freezing rain on Sunday afternoon. More details in the Short Term discussion below.

SHORT TERM /SUNDAY NIGHT/

A veil of high clouds will spread east and thicken-up Sunday morning, well in advance of the next weather system (an intense sfc low moving from the Western Great Lakes to the St. Lawrence River Valley Sunday afternoon through Monday night).

WAA ramps up a few to several KFT AGL as the wind flow in that layer increases from the southwest. The first mentions of precipitation come near/just after sunrise on Sunday with increasing low-level moisture progged by the bulk of model guidance.

Clouds will thicken-up quickly Sunday morning and if a 12 to 18 hour period of rain and drizzle, ahead of a warm/cold front tandem, arrives quicker than currently forecast, areal coverage of morning freezing rain could be greater. For now, we're expecting areas of freezing rain to be confined to the Mountains North and East of Williamsport and points east across the Poconos. A Winter Weather Advisory is in effect from 18Z/1PM Sunday to 06Z/1AM Monday where confidence is highest in a period of freezing rain (Lycoming, Sullivan, and Tioga County). Light icing is possible along ridgetops across Central PA, but the most widespread icing is expected in northeast PA.

Southerly flow will develop Sunday night and help usher in moderating temperatures as a warm front crosses the Commonwealth. Temperatures will rise throughout the night Sunday and reach their highest point Monday morning prior to the arrival of a cold front on Monday. As temperatures rise, the threat for freezing rain in northeast PA will end. Locally heavy rainfall is possible Sunday and Sunday night in northwest PA. A Marginal Risk of excessive rainfall is in effect for upstate NY, but localized totals of 1 to 1.5 inches are possible. Conewango Creek at Russell in Warren County, PA is expected to crest above caution stage on Tuesday as a result of the build up of snow melt and rainfall.

LONG TERM /MONDAY THROUGH SATURDAY/

The aforementioned, intense surface low will continue to track east across Southern Ontario and Southern as we head through Monday and Tuesday, allowing for a transition back into a rain/snow mix across the northwestern half of the forecast area with rain prevailing further southeast.

Westerly/northwesterly flow and an approx 25-30 deg F temp plunge during the day Monday/Monday evening behind the cold front promotes a combination of lake effect and upslope snow shower mentions across northwestern Pennsylvania through Thursday.

Recent NBM/LREF model guidance paints an impressive signal for gusty winds on Monday after the cold frontal passage with EC/GFS model guidance in fair agreement in a 850mb 70kt LLJ across the Laurel Highlands. Additionally, BUFKIT GFS Time Sections for KJST show 50 kt isotachs down below 500 ft AGL, and 60 kts at about 800 ft AGL. With the intense SFC low sliding by to our north, there's not a significant 3 hourly pressure rise (i.e., GRTN 5 mb/3 hr) accompanying the 30 deg F temp plunge on Monday.

We topped out winds in the low 50s (KTS) across the highest ridges just west of Interstate 99 and west of RT 219 in the Laurel Highlands. A High Wind Watch is now in effect from 15Z/10AM Monday through 18Z/1PM Tuesday for Bedford, Blair, Cambria, and Somerset Counties where we have the highest confidence in wind gusts over 60 mph. Widespread wind gusts of 45 to 55 mph are expected and Wind Advisories will be needed for much of the region in the next 24 to 36 hours.

In addition to the strong winds and cooler temperatures, the lake effect snow machine will get going again Monday afternoon through the New Year. A long duration lake effect and upslope snow event is anticipated with significant accumulation possible downwind of Lake Erie and in the Laurel Highlands. A west or southwesterly wind is favored for much of the week, which should direct the heaviest lake effect snow into NY, but several inches of snow are possible in Warren and McKean County. The Laurels will likely see multiple rounds of snow through the week as well, with the highest likelihood Monday into Tuesday and Wednesday into Thursday.

Cooler temperatures and wind chills also eek their way into the forecast for the New Year with wind chills dropping into the single digits and teens each morning through the New Year. Minimum wind chills for any outdoor New Year's Eve celebrations will be pushing into the single digits across northwestern Pennsylvania to the upper teens across the Lower Susquehanna Valley. Minimum temperatures by daybreak on New Year's Day range from 0 (NW) to the mid- teens (SE), with slightly cooler temperatures Thursday night into Friday morning.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At 00z, IFR/LIFR cigs were observed across the western highlands (BFD/JST) beneath a deck of very low clouds. Farther to the southeast, MVFR cigs (1500-2500 ft) were observed over the central mtns and Susq Valley.

Expect similar conditions to persist overnight. Some model guidance suggests that the low cloud deck could thin out in spots overnight, but the low clouds didn't budge today so I elected to keep them in place overnight as well. Something to watch.

Precipitation will overspread the area from west to east on Sunday. Mainly plain rain will fall, although a brief wintry mix cannot be ruled out across the northern tier of PA as the prcip begins. Any subtle improvement in cigs should reverse direction as the day progresses, with most locations dipping to IFR or low-end MVFR conds by aftn/eve.

A chc of rain showers will persist into Sun night and early Monday, before a sharp cold front crosses the region. After that, it looks like a wintry week is in store.

Outlook...

Mon...Mild early with widespread rain showers, then colder and windy later in the day with with snow showers across the N/W.

Tue...Windy and cold with snow showers N/W. Dry southeast.

Wed...Chance of snow showers across the north and west, dry southeast.

Thu...Chance of snow showers.

CTP WATCHES/WARNINGS/ADVISORIES

High Wind Watch from Monday morning through Tuesday afternoon for PAZ024-025-033-034. Winter Weather Advisory from 1 PM Sunday to 1 AM EST Monday for PAZ037-041-042-046.