textproduct: State College

SYNOPSIS

* Areas of freezing fog tonight into early Thursday morning * Widespread rain Thursday evening into early Friday morning followed by falling temperatures and lake-effect snow Friday * Strong winds Thursday night through Friday and again Sunday

NEAR TERM /UNTIL 6 AM THURSDAY MORNING/

Model guidance indicates areas of radiational [freezing] fog developing overnight under fair skies with light/variable wind and min temps in the 20s. As of 03z, already seeing patchy fog begin to form across the NW mtns. Any freezing fog could result in slick spots on untreated surfaces into early Thursday morning.

SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/

With warm air advection strengthening the existing temperature inversion Thursday morning, any fog and low clouds may be slow to dissipate. An increasingly moist SSE low level flow should favor low cloud cover expanding to the east of the Allegheny Front holding highs in the low to mid 40s.

Very strong 55-65kt LLJ will drive widespread rain ahead of a sharp cold front Thursday evening into early Friday morning. Rainfall totals are 0.50-1.00" for most with locally higher amounts >1" likely over the eastern periphery of the CWA, particularly where orographic enhancement will be maximized. Recent runs of the RRFS suggest the potential for a shallow, strongly forced cold frontal rain band feature to sweep through btwn 06-12Z Fri and would not rule out sporadic ltg and rumbles of thunder within the convective line and/or with elevated pre- frontal convective elements.

Temperatures will be non-diurnal (steady to rising) Thursday night, before colder air begins to advect into the western highlands towards daybreak. A persistent flow of colder air behind the front will continue the non-diurnal (falling) trend on Friday.

A tightening pressure gradient and sfc pressure rises within broad CAA regime will deliver strong gusty winds on Friday. Max gusts in the 35-45 mph range are probable with higher gusts exceeding advisory level criteria certainly within reach. Odds for a NPW headline are better than 50/50 and we considered a CWA-wide headline for this cycle; however will allow the next shift to further assess and collaborate. We continue to highlight the high wind threat in the HWO. The strongest wind gusts are most likely on Friday, however can't rule out some locally higher gusts on the ridgetops Thursday night given the magnitude of LLJ.

Short duration lake-effect snow accums in the 1-3" range are likely across the NW mtns Friday-Friday night.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Arrival of sfc high ends LES by early Saturday. Model data continues to show a strong cold frontal passage with quick shot of arctic air Sunday-Sunday night along with gusty winds and lake effect snow. SNSQ risk should also be monitored.

The cold air retreats through early next week, setting up a possible overrunning mixed precip event for Tuesday. The weather for Christmas Eve looks fair and seasonable with no major travel impacts expected at this time.

AVIATION /03Z THURSDAY THROUGH MONDAY/

Mid evening update.

An interesting evening so far.

Winds at MDT went calm, then got gusty last hour, resulting in the temperature jumping up there.

On the other end, BFD went calm with fog and low CIGS.

Another interesting feature on radar, just north of the office. Perhaps what remains of the cold front that was located to the north of the area earlier.

Anyway, more in the fog and even some lower CIGS may form overnight, as temperatures drop to below the dewpoints. However, dewpoints may fall as well, given the very dry air not very far above the ground.

In addition, LLWS across the far west, BFD and JST, later tonight into Thursday.

Some more input as of late afternoon.

Added a group for low CIGS late Thursday afternoon, as the southeast flow brings in lower clouds. Most likely spots to see this is LNS, MDT, and perhaps IPT, Locations to the west may not have lower CIGS before 00Z Friday, will be close, for now did include them as well.

Still expect most of Thursday to be dry with VFR conditions. Showers later in the day.

Outlook...

Fri...Gusty W wind (40+ kts possible). MVFR w/SCT SHSN at JST/BFD. Mainly VFR elsewhere.

Sat-Sun...MVFR-IFR BFD in SCT -SHSN. VFR cigs favored elsewhere.

Mon...Trending drier with VFR favored. Snow enters W PA late evening with restrictions possible.

CLIMATE

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

CTP WATCHES/WARNINGS/ADVISORIES

None.