077
FXUS61 KCTP 131029
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
529 AM EST SAT DEC 13 2025
SYNOPSIS
* A PERIOD OF ACCUMULATING, THOUGH MAINLY LIGHT SNOW IS EXPECTED
TO BEGIN THIS AFTERNOON ACROSS THE WEST AND EARLY THIS EVENING
OVER THE SUSQUEHANNA VALLEY. THE SNOW WILL CONTINUE INTO
EARLY SUNDAY, FOLLOWED BY ANOTHER ARCTIC BLAST AND LOCALLY
HEAVY LAKE EFFECT AND UPSLOPE SNOW ACROSS NW PA.
* THE NORTHWEST WIND WILL BECOME GUSTY ON SUNDAY LEADING TO
POTENTIALLY DANGEROUS WIND CHILLS WHEN COMBINED WITH THE COLD
AIR.
* A PERIOD OF MILDER CONDITIONS IS EXPECTED FOR THE MIDDLE OF
THE WEEK AHEAD.
NEAR TERM /UNTIL 6 PM THIS EVENING/
SFC HIGH PRESSURE JUST EAST OF THE DELAWARE COAST EARLY THIS
MORNING HAS A RIDGE EXTENDING NORTH ACROSS THE HUDSON VALLEY OF
NEW YORK STATE. WIDESPREAD MID AND HIGH CLOUDS WERE SPREADING
EAST AND OVER THIS RIDGE, AND PRECIP WE'RE SEEING ON REGIONAL
MRMS RADAR MOSAIC.
A LARGE AREA OF LIGHT SNOW ASSOCIATED WITH THE LEFT EXIT REGION
OF A 90-100 KT WESTERLY JET AT 500 MB WILL BEGIN ACROSS THE
LAUREL HIGHLANDS FIRST - DURING THE EARLY TO MID AFTERNOON,
BEFORE EXPANDING NORTHWARD ACROSS THE ALLEGHENIES FOR THE LATE
AFTERNOON.
TEMPS TO START THE DAY TODAY WILL RANGE FROM 10 TO 15 DEGREES
ACROSS THE NORTH TO UPPER TEENS AND LOW 20S IN THE SOUTHEAST.
AFTERNOON HIGHS WILL REACH 25 TO 30 ACRS THE NORTHERN AND
WESTERN MOUNTAINS AND MID 30S TO LOWER 40S RESPECTIVELY FROM
THE CENTRAL VALLEYS TO THE GREATER PHILADELPHIA AREA.
SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/
THE AFOREMENTIONED SURFACE LOW/CLIPPER SYSTEM WILL ARRIVE
SUNDAY AFTERNOON SUPPORTED BY A DIGGING 500MB TROUGH AND PLUME
OF MOISTURE FROM THE PACIFIC NORTHWEST US. SNOW WILL BE THE
RESULT OF A FAST MOVING COLD FRONT AND STRONG UPPER LEVEL JET
DYNAMICS MOVING WITH THIS TROUGH. THE DEEP TROUGH AND STRONG
FORCING/COLD AIR ALOFT WILL RESULT IN MODERATE SNOW OVER MOST
OF WESTERN PENNSYLVANIA WITH WIDESPREAD LIGHT SNOW OVER THE
REMAINDER OF THE STATE. UPSLOPE WILL AID IN SNOWFALL EFFICIENCY
RESULTING IN THE HIGHEST SNOWFALL AMOUNTS ACROSS THE LAUREL
HIGHLANDS AND IN THE NORTHWEST MOUNTAINS. A LOW PRESSURE CENTER
WILL DEVELOP SOUTH OF PENNSYLVANIA BY LATE SATURDAY AFTERNOON,
BUT WILL QUICKLY MOVE OFF THE COAST, ALLOWING FOR ADDITIONAL
SNOW TO FALL OVER THE SOUTHEAST AND LOWER SUSQUEHANNA VALLEY.
UNCERTAINTY IS GREATEST WITH THIS LOW; HOWEVER, AND THE SPEED
AND POSITION COULD LIMIT THE SNOWFALL TOTALS.
BY LATE SUNDAY MORNING THE SYNOPTIC SNOW WILL LARGELY BE OVER,
BUT UPSLOPE AND LAKE EFFECT PRECIPITATION WILL PERSIST IN THE
WEST ALONG WITH A DEEP ARCTIC AIRMASS. A TIGHT PRESSURE
GRADIENT IS EXPECTED ON THE BACK SIDE OF THE DEPARTING UPPER
LEVEL TROUGH, AND AN 850MB JET STREAK WILL TRANSFER SIGNIFICANT
MOMENTUM TO THE SURFACE. WIND GUSTS UP TO 40MPH ARE POSSIBLE
OVER THE LAURELS, AND WITH REINFORCING COLD AIR COULD BRING
DANGEROUS WINDCHILLS TO THE REGION ON SUNDAY. MIN WIND CHILLS
NEAR AND BELOW ZERO SATURDAY NIGHT THROUGH SUNDAY NIGHT/AM
MONDAY ARE VERY LIKELY. MAX TEMPS SUNDAY WILL DROP BY 10-20
DEGREES VS. SATURDAY WITH MEAN DEPARTURES FROM CLIMO ON THE
ORDER OF 15 TO 25 DEGREES. A FEW LOCATIONS COULD SEE HIGHS CLOSE
TO THE DAILY RECORD LOW MAX.
LAKE EFFECT/UPSLOPE SNOW SHOWERS CONTINUE THROUGH SUNDAY NIGHT
INTO MONDAY BEFORE HIGH PRESSURE BEGINS TO BUILD IN FROM THE
SOUTH AGAIN.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
WINDS BY TUESDAY SHIFT MORE TO THE WEST, THEN TO THE SOUTHWEST
BY WEDNESDAY, AS A LARGE HIGH PRESSURE SYSTEM MOVES EASTWARD
TO THE SOUTHEAST STATES. THE LARGE SCALE FLOW PATTERN BECOMES
MORE ZONAL, AS UPPER LEVEL HEIGHTS RISE TO MUCH HIGHER VALUES
THAN WE HAD SEEN LATELY. THIS WILL SET THE STAGE FOR TEMPERATURES
CLIMBING TO ABOVE NORMAL, AT LEAST FOR THE PERIOD WEDNESDAY
INTO LATE THURSDAY.
A COLD FRONT BY FRIDAY WILL EDGE THINGS BACK DOWN SOME, BUT NOT
THE REALLY COLD THAT HAS BEEN TYPICAL THIS MONTH SO FAR. THE
MONTH HAS BEEN NEARLY 10 DEGREES COLDER THAN NORMAL UP TO THIS
POINT, WHICH IS NEARLY HALF OF DECEMBER.
EARLIER DISCUSSION BELOW.
ONE MORE SHORTWAVE TROUGH COULD BRUSH THE AREA WITH LIGHT SNOW
EARLY NEXT WEEK; OTHERWISE THERE IS GROWING CONFIDENCE IN A MID
TO LATE DECEMBER THAW AS THE PATTERN TRANSITIONS TO A MILDER SW
FLOW ALOFT WITH MEAN TROUGHING SHIFTED WESTWARD INTO THE CENTRAL
U.S. DRY WX IS FAVORED TUE-THU WITH HIGHS CLIMBING TOWARD THE
40-50F RANGE LATE IN THE WEEK - POSSIBLY IN ADVANCE OF THE NEXT
WIDESPREAD PRECIP EVENT.
AVIATION /09Z SATURDAY THROUGH WEDNESDAY/
CLOUDS WILL THICKEN UP FROM THE WEST EARLY THIS MORNING, WITH
MVFR CIGS SPREADING INTO UNV AND IPT BY 11-16Z. ANY SNOW DURING
THE DAYLIGHT HOURS WILL LIKELY BE ON THE LIGHT SIDE. JST HAS THE
HIGHEST CHANCE OF MVFR VSBY RESTRICTIONS AND IFR CIG
RESTRICTIONS PRIOR TO 21Z. AS STEADIER SNOW MOVES IN AFTER
SUNSET, A 4-8HR PERIOD OF LIFR VSBY WILL BE POSSIBLE AT JST.
IFR VSBYS ARE LIKELY AT BFD AND AOO TONIGHT, BUT CHANCES ARE
LOWER FOR IPT AND UNV AS SNOWFALL INTENSITY WILL WEAKEN AS
PRECIP CROSSES THE ALLEGHENY FRONT. HOWEVER, ANOTHER AREA OF
FORCING IS PROGGED TO INITIATE AN AREA OF STEADY LIGHT TO
MODERATE SNOW IN THE LOWER SUSQ VALLEY, LIKELY IMPACTING MDT AND
LNS WITH IFR VSBYS AFTER 02Z SUN AND CONTINUING THROUGH 07-09Z.
LNS WILL LIKELY BE WORSE THAN MDT WITH THE HEAVIEST SNOW
FALLING TO OUR SE (PHILLY/DC).
IT WILL GET WINDY (GUSTS 25-35KT) ON SUN AND INTO EARLY SUN
NIGHT AS VERY COLD AIR MOVES IN. THE WESTERN TERMINALS (BFD AND
JST) MAY HAVE A FEW HOUR BREAK SUN AM WITH LITTLE SNOW BEFORE
LAKE EFFECT KICKS BACK IN, AND CIGS/VSBYS DROP AGAIN SUN LATE
AM/AFTN.
OUTLOOK...
SUN...SHSN/IFC LINGER IN WESTERN HIGHLANDS. MVFR CIGS/ISOLD
SHSN AOO/UNV. MVFR/VFR CIGS ELSEWHERE. GUSTY WEST WIND.
MON...MVFR W/SCT SHSN BFD, NO SIG WX ELSEWHERE.
TUE-WED...NO SIG WX.
CLIMATE
ASTRONOMICAL WINTER (SOLSTICE) BEGINS AT 10:03 A.M. ON SUNDAY,
DECEMBER 21ST.
CTP WATCHES/WARNINGS/ADVISORIES
LAKE EFFECT SNOW WARNING FROM 10 AM THIS MORNING TO 7 AM EST
MONDAY FOR PAZ004-005.
WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 7 AM EST
MONDAY FOR PAZ010-017-024-033.
WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST
SUNDAY FOR PAZ065-066.
SYNOPSIS...LAMBERT/BOWEN
NEAR TERM...LAMBERT/BOWEN
SHORT TERM...LAMBERT/BOWEN
LONG TERM...MARTIN/NPB
AVIATION...GARTNER/COLBERT
CLIMATE...STEINBUGL
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