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SYNOPSIS

*Widespread soaking rainfall tonight into early Friday morning; brief heavy rain possible along cold front/convective line *Increasingly windy tonight through Friday; max gusts 50-60 mph *Rain ends early Friday followed by falling temperatures and snow showers into Friday night

NEAR TERM /UNTIL 6 AM THIS MORNING/

Steady rain will continue through much of the night as a 50 to 70 knot low-level jet continues to transport higher PWAT air in from the south. A narrow rain band along a cold front will track through Central PA in the ~06-13Z timeframe. Brief heavy rainfall and sporadic ltg flashes/thunder rumbles are possible. There may be a short window of convectively augmented wind gusts right along the thin line, but cool BL/near zero SBCAPE, early time of day, and limited lapse rates aloft suggest minimal overall damaging wind risk.

Rainfall totals ticked higher vs. previous with much of CPA expected to pick up 0.50-1" of rain; max amounts 1.5-2.5" are focused over the east-central portion of the fcst area. Minor flooding/small stream issues are not out of the question in this area given elevated terrain and snowmelt/ice contributions (see hydro section).

Non-diurnal temps overnight leveling off and gradually rising toward daybreak.

SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY NIGHT/

A persistent flow of colder air behind the front will result in falling temperatures through the day on Friday. A tightening pressure gradient, steepening low level lapse rates and +3-6mb/3hr sfc pressure rises within broad CAA regime will deliver strong gusty winds into Friday night. Max gusts in the 40-50 mph range are expected across the CWA with the highest gusts up to 60 mph in the Laurel Highlands/south central Alleghenies. A high wind warning was issued for Cambria, Somerset, Blair, and Bedford Counties. The period of strongest winds is most likely between 1PM and 7PM Friday as the diurnal mixing in the BL taps into the strong WNW winds aloft.

After the soaking rain ends Friday morning, surge of colder air will trigger snow showers downwind of Lake Erie and over the western mtns by midday before spreading eastward through the remainder of the day. Favored upslope locations and lake effect snow belts should pick up 1-3" by 12Z Saturday; a winter wx advisory may be needed in the NW mtns where locally higher amounts are possible (particularly in Warren County) along with blowing/drifting snow travel impacts. The lake effect snow (LES) will be shorter in duration compared to some events earlier this season.

Arrival of sfc high pressure drops the wind and ends LES by early Saturday morning and provides a fair/seasonable start to the weekend before Christmas.

LONG TERM /SUNDAY THROUGH THURSDAY/

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 couple potential overrunning mixed precip events for early Tuesday and again on Christmas Day. Timing will be critical for any winter wx impacts as max temperatures are forecast to trend above the historical average for late December.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

Rain has overspread the region and will continue to bring lowered conditions wet runways throughout the rest of tonight and into the morning hours today. Most airfields will experience IFR tonight, with high confidence (>80%) of occurrence. Along with the rain LLWS will be persistent at most airfields until around 12Z this morning.

The cold front bringing these conditions will move in early Friday across the west, and mid to late morning further east. Winds will be on the increase along and behind the front. Strongest winds expected at AOO and JST with confidence increasing in 40+ knot gusts during the day as mixing occurs with the mid levels. Most airfields will become dry behind the cold front, but some upslope and lake effect snow showers could persist into Friday evening across the west, mainly at BFD and JST. Prob 30s have been added where confidence is lower in precipitation occurring. Expect IFR to MFVR ceilings to persist into early friday afternoon, before slow improvements will occur area wide.

Outlook...

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.

Tue...Rain/snow becomes increasingly possible, restrictions possible.

HYDROLOGY

1.5-2.0" of rainfall in a 12-18hr duration ending 1PM Friday could result in some minor flooding issues over the east-central mtns particularly in Sullivan County where storm total max rainfall could exceed 2". Snowmelt (up to 1" of SWE) and ice effects could also play a role in contributing to isolated minor flooding issues.

CLIMATE

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

CTP WATCHES/WARNINGS/ADVISORIES

Wind Advisory until 1 AM EST Saturday for PAZ004>006-010>012- 017>019-026>028-035>037-041-042-045-046-049>053-056>059- 063>066. High Wind Warning until 1 AM EST Saturday for PAZ024-025-033- 034.