931
FXUS61 KCTP 180959
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
459 AM EST WED DEC 18 2024
SYNOPSIS
* PRECIPITATION ARRIVES THIS AFTERNOON WITH RAIN LIKELY SOUTH
OF I-80 AND SNOW OR A WINTRY MIX ACROSS THE NORTHERN MOUNTAINS
* A CLIPPER WILL BRING LIGHT SNOW TO MOST OF THE AREA ON FRIDAY
* CONSIDERABLY COLDER FOR THE WEEKEND.
NEAR TERM /UNTIL NOON TODAY/
A WEAK AREA OF SURFACE HIGH PRESSURE IS CENTERED OVER SOUTHEAST
PA THIS MORNING WITH CLEAR SKIES AND CALM WINDS AT THE
SURFACE ACROSS MUCH OF THE LOWER SUSQUEHANNA VALLEY. PATCHY FOG
REMAINS POSSIBLE THERE THROUGH MID MORNING.FARTHER NORTHWEST,
WARM ADVECTION PRECEDING AN UPSTREAM TROUGH IS LEADING TO
INCREASING CLOUDINESS FROM JOHNSTOWN NORTHEAST THROUGH
WILLIAMSPORT EARLY THIS MORNING. MORNING LOWS ARE ON PACE TO BE
A COUPLE DEGREES ABOVE OR BELOW 30F AREAWIDE.
THE DECK OF HIGH CLOUDS WILL CONTINUE TO SHIFT EASTWARD ACROSS
PENNSYLVANIA THIS MORNING AHEAD OF A A WEAK AND FAST-MOVING SURFACE
LOW MOVING THROUGH THE OHIO VALLEY. MOST LOCATIONS SHOULD STAY
DRY THROUGH LUNCHTIME WITH HIGH TEMPERATURES (PRIOR TO
PRECIPITATION ONSET) RANGING FROM THE MID 30S IN THE NORTHWEST
MOUNTAINS TO NEAR 50 IN EXTREME SOUTHEAST PA.
SHORT TERM /NOON TODAY THROUGH THURSDAY NIGHT/
PRECIPITATION WILL OVERSPREAD FROM SOUTHWEST TO NORTHEAST PRETTY
QUICKLY THIS AFTERNOON. LIMITED COLD AIR AND LACK OF A BLOCKING
HIGH SHOULD RESULT IN MOST PRECIPITATION FALLING AS RAIN, WITH
ONLY A RELATIVELY NARROW SWATH OF SNOW ON THE NORTHERN PERIPHERY
OF THE PRECIP SHIELD OVER THE N MTNS. STRONG WARM ADVECTION IS
NOTED IN THE MODEL GUIDANCE AT THE NOSE OF A 50KT LOW LEVEL JET,
WHICH SUPPORTS POPS NEAR 100PCT DURING THE AFTERNOON TO EARLY
EVENING.
EXPECT PRECIPITATION TO TAPER OFF FROM WEST TO EAST THIS
EVENING, AS THE WAVE OF LOW PRESSURE SLIDES EAST OF PA. ENSEMBLE
MEAN QPF BY THIS EVENING RANGES FROM 0.15 TO 0.40 INCHES, WITH
THE HEAVIEST AMOUNTS OVER SOMERSET AND SCHUYLKILL COUNTIES,
WHERE OROGRAPHIC ENHANCEMENT IS MAXIMIZED. FORECAST SOUNDINGS
INDICATE SNOW WILL BE CONFINED TO THE N MTNS WEDNESDAY, WHERE
1-2 INCHES ARE POSSIBLE OVER THE HIGHER TERRAIN.
RESIDUAL LOW LEVEL MOISTURE ASCENDING THE ALLEGHENIES SHOULD
RESULT IN LINGERING LIGHT RAIN/SNOW OVER THE WESTERN COUNTIES
EARLY THIS EVENING, WHILE A DOWNSLOPING NORTHWEST FLOW RESULTS
IN DEVELOPING BREAKS IN THE OVERCAST FURTHER EAST. THE AIRMASS
CROSSING THE GRT LKS THEN BECOMES COLD ENOUGH TO SUPPORT
SCATTERED, OROGRAPHICALLY-ENHANCED, LAKE EFFECT SNOW SHOWERS
OVER THE W MTNS LATE WED NIGHT. LOW INVERSION HEIGHTS INDICATE
ANY ACCUMULATIONS WILL BE VERY LIGHT (<0.5 INCHES). MODEL
SOUNDINGS ACTUALLY INDICATE SHALLOW CLOUD DEPTHS MAY RESULT IN
PATCHY -FZDZ, RATHER THAN -SHSN, OVER THE RIDGETOPS OF THE
LAUREL HIGHLANDS.
THE WINDOW FOR LAKE EFFECT SNOW SHOWERS OVER NW PA EXTENDS INTO
MIDDAY THURSDAY WITH GENERALLY LIGHT ACCUMS EXPECTED. TYPICAL
NORTHWEST FLOW PATTERN ON THURSDAY WITH BREAKS IN THE CLOUDS IN
SE PA DURING THE AFTERNOON AND PERSISTENT STRATOCUMULUS FARTHER
NORTHWEST. HIGHS ON THURSDAY WILL TREND CLOSE TO NORMAL WITH
HIGHS IN THE LOW 30S TO LOW 40S. AN APPROACHING CLIPPER SYSTEM
WILL TURN WINDS EASTERLY THURSDAY NIGHT, SUPPORTING A DRY BUT
DREARY NIGHT WITH PLENTY OF LOW CLOUDS AND PERHAPS SOME REDUCED
VISIBILITY. LOWS IN THE MID 20S WILL COOL THE GROUND ENOUGH TO
ALLOW ANY SNOW THAT FALLS ON FRIDAY TO STICK TO
UNTREATED/ELEVATED SURFACES.
LONG TERM /FRIDAY THROUGH TUESDAY/
10PM UPDATE...AFTER THE FRIDAY CLIPPER IT WILL BE VERY COLD,
WITH MAXES ONLY IN THE 20S-L30S SATURDAY AND MIDTEENS-MID20S
SUNDAY. OVERNIGHT LOWS LIKELY CHALLENGE 0F IN THE N (SUN AM).
ALMOST EVERYONE WILL DROP INTO THE SINGLE DIGITS MON AM. WIND
CHILLS DO GET NEAR -10F SUN AM IN THE NE, BUT NOT ON MON AM
WHEN THE WIND IS LIGHTER/CALM UNDER THE SFC HIGH DESPITE THE
COLDER AIR TEMPS.
PREV...
A MOISTURE CHALLENGED CLIPPER SYSTEM WILL BRING A PERIOD OF
LIGHT SNOW OR SNOW SHOWERS OVER WESTERN AND CENTRAL PARTS OF PA
ON FRIDAY. THIS FEATURE LOSES ITS SURFACE REFLECTION LATE FRIDAY
AS ITS PARENT UPPER TROUGH PHASES OFF THE MID ATLANTIC SHORE TO
STRENGTHEN AN OCEAN STORM THAT RACES SOUTHEAST OF NEW ENGLAND
FRI NIGHT AND SATURDAY. RESIDUAL DEFORMATION ZONE FLURRIES OR
SNOW SHOWERS APPEAR LIKELY FRIDAY NIGHT INTO EARLY SATURDAY OVER
MAINLY THE ALLEGHENIES AND N CENTRAL MOUNTAINS, FOLLOWED BY
SOME LAKE EFFECT SNOW SHOWERS INTO THE NW MOUNTAINS FOR THE
REMAINDER OF SATURDAY AND INTO SUNDAY. ACCUMS WITH THE CLIPPER
FRIDAY APPEAR LIGHT, GENERALLY A COATING ACROSS CENTRAL AREAS
AND A COATING TO PERHAPS A FEW INCHES OVER THE HIGHER WESTERN
AND NORTHERN TERRAIN, WITH ADDITIONAL LIGHT LAKE EFFECT ACCUMS
CONFINED TO THE NW MOUNTAINS. EVEN COLDER CONDITIONS ARRIVE FOR
SUNDAY AS THE ARCTIC HIGH BUILDS OVER NW PA SUNDAY NIGHT
PRODUCING WIDESPREAD MINS IN THE SINGLE DIGITS ABOVE ZERO MONDAY
MORNING.
AVIATION /10Z WEDNESDAY THROUGH SUNDAY/
BFD GOT TO IFR A LITTLE QUICKER THAN PLANNED, AND IPT GOT SOME
FOG QUICKLY, TOO. HAVE ADJUSTED TIMING THERE.
PREV...
VFR EVERYWHERE WILL CONTINUE FOR MOST OF THE NIGHT AT PERHAPS
ALL BUT BFD AND IPT. LOW CLOUDS WILL WORK DOWN FROM THE NW AND
DIP BFD INTO MVFR EARLY TONIGHT AND THEN TO IFC AROUND OR
SHORTLY AFTER MIDNIGHT/05Z. IPT HAS HIGH MOISTURE LINGERING AT
THE SFC AND THE CALM AIR MAY ALLOW FOG TO FORM AND EVENTUALLY
TAKE THEM INTO IFC LATE TONIGHT. MDT AND LNS, TOO, HAVE HIGHER
MSTR, AND COULD GET FOGGY BEFORE SUNRISE. 50% CHC THAT THOSE 2
SERN TERMINALS WILL GET INTO IFC, BUT 80% AT IPT.
LOW PRESSURE PASSING ACROSS SRN PA WEDNESDAY WILL BRING RAIN TO
ALL TERMINALS EXCEPT BFD - WHERE THE PREDOMINANT PRECIP TYPE
WILL BE SNOW. HOWEVER, THIS WILL BE A QUICK SHOT OF PRECIP (6
HRS). THE VISBY WILL DROP TO IFC QUICKLY, BUT COULD POP BACK UP
TO MVFR AS THE PRECIP TAPERS OFF AROUND 23-01Z. THE WIND JUST
ALOFT (2-3KFT) GETS UP TO 35KT IN THE S AND THE LIGHT SFC WIND
WILL NECESSITATE A MENTION OF LLWS FOR THE LAST 6HRS OF THIS TAF
PKG (18Z WED-00Z THURS) FOR ALL BUT BFD AND IPT.
LAKE EFFECT CLOUDS AND SNOW SHOWERS THEN START FOR BFD AS THIS
SYSTEM DEPARTS WED NIGHT AND LINGER INTO THURSDAY. IFR IS
POSSIBLE THERE AND JST IN THE UPSLOPE FLOW, BUT CLOUDS AND ANY
FLURRIES ELSEWHERE WILL ONLY BE GOOD FOR MVFR CIGS/VSBYS.
A CLIPPER SYSTEM ROLLS OVERHEAD ON FRIDAY, PRODUCING WIDESPREAD
IFC IN SNOW/CIGS. THE SE (MDT AND LNS) MAY BE WARM ENOUGH FOR
RAIN.
OUTLOOK...
FRI...IFR POSSIBLE IN SNOW NW & RAIN SE.
SAT-SUN...MVFR CIGS IN SHSN @ BFD/JST. MAINLY VFR ELSEWHERE.
CLIMATE
ASTRONOMICAL WINTER (SOLSTICE) BEGINS ON SATURDAY, DECEMBER 21ST
AT 4:19 A.M. EST.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...BANGHOFF
NEAR TERM...FITZGERALD/BANGHOFF
SHORT TERM...FITZGERALD/BANGHOFF
LONG TERM...LAMBERT/DEVOIR/DANGELO/BAUCO
AVIATION...DANGELO
CLIMATE...STEINBUGL
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