textproduct: State College

SYNOPSIS

* Light snow ends in NW PA; round 2 on the way Wednesday morning * Windy with wet snow and mixed precipitation Wednesday followed by lake effect/upslope snow showers through Thursday night * Periods of snow and below normal temperatures Friday through the weekend

NEAR TERM /THROUGH TONIGHT/

A quick shot of light snow across the NW mtns will end early this evening. Elsewhere, expect cloudy skies with steady/flat to slowly rising (non-diurnal) temps overnight as WAA ramps up ahead of fast moving/intense clipper low racing eastward from southwest MN to lower MI by 12Z Wednesday. Min temps occur early tonight in the low to mid 20s.

SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/

The strong WAA downstream from the clipper low will overrun a retreating cold antecedent airmass, creating broadening plume of precip, falling primarily as wet snow across the NW Alleghenies during the predawn hours impacting the morning commute. HREF/RRFS model signals suggest a brief period of zr/sleet is possible along the southeast edge of the precip shield near the I81 corridor (strongest ice signal is over Schuylkill County). Later shifts can assess potential for SPS or short-fused winter wx advisory (low confidence, but non-zero prob of ice glaze).

No significant changes to expected snowfall totals with max amounts 2-5" over the northern tier/Route 6 corridor. Local max ~6" may be found in the higher terrain in Sullivan County. Snow rates are projected to be in the 0.50-1 in/hr range in the NW mtns during the 5-10AM window before shifting eastward across north central PA toward the Poconos.

Intermittent snow/rain in the valleys along I99/US220 corridor from Blair/Centre County east along I80/US220 should result in a slushy coating to 1 inch. There is a scenario where wetbulb effects help to lock in colder air for a longer duration over the central ridge/valley region, which may result in a bit more snow than currently fcst. Temps are expected to rise above the freezing mark particularly along and southeast of I99/I80 corridor by the afternoon. Temps could stay a few degrees colder in the northern tier, but road snow will likely become more limited after midday given the marginal air/road temps.

We expanded the winter wx advisory to include the Laurel Highlands in coordination with PBZ/LWX. Rain to snow transition occurring over the course of the day on Wednesday will be followed by an extended period of orographically enhanced snow showers with blustery winds through Wednesday night as the strong storm tracks northeast through the St. Lawrence River Valley. We could foresee the advisory being extended for the NW mtns where additional LES accums are expected into Thursday.

Winds increase tomorrow with frequent gusts in the 25-35 mph range; locally higher gusts up to 40 mph on the Laurel Highlands. Given the wet character of the snow early on Wednesday, blowing and drifting impacts are not a concern at least initially. However, as temps fall into Wednesday night, expect the character of the snow to become drier or more fluffy which increases the potential for blowing and drifting over the higher terrain Wednesday evening through Wednesday night. Wet surfaces and slush areas will be prone to refreezing and icy spots overnight Wednesday into early Thursday morning.

LONG TERM /THURSDAY THROUGH TUESDAY/

Lake effect snow showers and gusty northwesterly winds continue on Thursday with additional snow accums expected over the northwestern mountains and Laurel Highlands. A few long fetch bands or locally heavy snow showers/squalls are possible on Thursday and could extend as far southeast as I81.

Winter weather/periods of snow continue from Friday through the weekend and into early next week with a series of upper troughs and clippers followed by reinforced cold NW flow and lake effect/upslope snow showers. Temperatures remain below the historical average heading into mid-December.

AVIATION /19Z TUESDAY THROUGH SUNDAY/

Mainly VFR conds were reported at 19z Tue. An area of stratus at 3500-4500 ft continues to push across east-central PA. Just east of the Allegheny Front, most cigs are up near 10,000 feet. West of the Alleghenies, another area of stratus associated with a warm front is pushing eastward with cigs near 4000-5000 ft. The warm front has also produced a few areas of light snow in western PA. Vsby reductions due to snow are possible at BFD mainly 19z-00z. Winds during the day will be out of the south at 10 to 15 knots with gusts up to 20 knots.

MVFR ceilings will expand east tonight, likely arriving at JST, AOO, IPT, and UNV within a couple hours of sunrise. A clipper system system will bring periods of light to moderate snow to the region on Wednesday morning and into the afternoon, initially moving into BFD in the 06-09Z timeframe. Precipitation will be much lighter south of UNV and east of AOO, but a mix of rain, snow, and freezing rain is possible at MDT and LNS during the late morning and early afternoon.

LLWS will also become a factor tonight into Wednesday as a 45-60 knot west-southwesterly LLJ moves into western PA after 00Z Wednesday. Behind the cold front Wed evening into Thu, winds will turn out of the west and increase with sfc gusts 15-35 kts (highest in the Laurels).

Outlook...

Wed night-Thu...Snow showers continue, mainly N/W PA. Windy.

Fri-Sun...Additional rounds of light snow possible with multiple clipper systems.

CLIMATE

Bradford, PA had two records in one night! Their temp of -4F just before midnight EST on 12/8 broke the previous record of -2F set in 1970. As the temp continued falling through the night, they tied the 12/9 record low of -12F at 6 AM EST. This tied the record set in 2002.

Astronomical winter (solstice) begins at 10:03 a.m. on Sunday, December 21st.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 1 AM to 10 PM EST Wednesday for PAZ004>006-010>012-017-018. Winter Weather Advisory from 10 AM Wednesday to 10 AM EST Thursday for PAZ024-033. Winter Weather Advisory from 3 AM to 10 PM EST Wednesday for PAZ037-041-042.