236
FXUS61 KCTP 180156
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
856 PM EST TUE DEC 17 2024
SYNOPSIS
* PRECIPITATION WEDNESDAY AFTERNOON AND EVENING WITH RAIN
LIKELY SOUTH OF I-80 AND SNOW OR A WINTRY MIX ACROSS THE
NORTHERN MOUNTAINS
* LAKE EFFECT SNOW SHOWERS WEDNESDAY NIGHT AND THURSDAY
* A CLIPPER WILL BRING LIGHT SNOW ON FRIDAY
* CONSIDERABLY COLDER FOR THE WEEKEND.
NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/
A WEAK AREA OF SURFACE HIGH PRESSURE OVER WV WILL TRACK ACROSS
THE SOUTHERN TIER OF PA TONIGHT, PROVIDING FAIR WEATHER TO THE
REGION. MAINLY CLEAR SKIES AND CALM WIND SHOULD PROMOTE PATCHY
VALLEY FOG OVERNIGHT, PRIMARILY IN THE MIDDLE SUSQ VALLEY, WHERE
DEWPOINT DEPRESSIONS ARE ALREADY APPROACHING ZERO AS OF 01Z.
WARM ADVECTION PRECEDING AN UPSTREAM TROUGH WILL RESULT MORE
CLOUDINESS ACROSS THE NORTHWEST PORTION OF THE FORECAST AREA
TONIGHT, LIMITING THE FOG POTENTIAL UP THERE. TEMPERATURES MAY
FALL A BIT BELOW NBM GUIDANCE ACROSS THE SOUTHERN COUNTIES,
WHERE CONDITIONS ARE MOST FAVORABLE FOR RADIATIONAL COOLING. IN
GENERAL, EXPECT LOW TEMPS TO BE IN THE UPPER 20S TO LOW 30S.
SHORT TERM /7 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/
ALL NEAR TERM MODEL GUIDANCE TRACKS A WEAK AND FAST-MOVING SURFACE
LOW NORTHEAST FROM THE OHIO VALLEY ON WEDNESDAY, PASSING JUST
SOUTH OF THE MASON DIXON LINE DURING THE LATE AFTERNOON AND
EARLY EVENING HOURS.
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.
18Z GUIDANCE AND EARLIER HREF INDICATED PRECIP ARRIVAL TIMES
RANGING FROM 15Z-18Z FROM WEST TO EAST.
EXPECT PRECIPITATION TO TAPER OFF FROM WEST TO EAST WED EVENING,
AS THE WAVE OF LOW PRESSURE SLIDES EAST OF PA. ENSEMBLE MEAN QPF
BY WED 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.
HAVE STUCK CLOSE TO NBM TEMPS WED DUE TO LACK OF A STRONG COLD
AIR DAMMING SIGNATURE. EXPECT MAX TEMPS TO RANGE FROM THE MID
30S OVER THE N MTNS, TO THE UPPER 40S ACROSS THE LOWER SUSQ
VALLEY.
RESIDUAL LOW LEVEL MOISTURE ASCENDING THE ALLEGHENIES SHOULD
RESULT IN LINGERING LIGHT RAIN/SNOW OVER THE WESTERN COUNTIES
EARLY WED 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.
LONG TERM /THURSDAY THROUGH TUESDAY/
THE WINDOW FOR LAKE EFFECT SNOW SHOWERS OVER NW PA EXTENDS INTO
MIDDAY THURSDAY WITH GENERALLY LIGHT ACCUMS EXPECTED. A
MOISTURE CHALLENGED CLIPPER SYSTEM DROPPING THROUGH THE UPPER
MIDWEST THURSDAY AND THURSDAY NIGHT WILL INITIATE WAA BY LATER
THURSDAY SHUTTING OFF THE LAKE EFFECT, BUT BRINGING A POTENTIAL
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 /01Z WEDNESDAY THROUGH SUNDAY/
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...LAMBERT
NEAR TERM...FITZGERALD
SHORT TERM...LAMBERT/FITZGERALD
LONG TERM...LAMBERT/DEVOIR/DANGELO/BAUCO
AVIATION...DANGELO
CLIMATE...STEINBUGL
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