851
FXUS61 KCTP 130318
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1018 PM EST FRI DEC 12 2025
SYNOPSIS
* A PERIOD OF ACCUMULATING SNOW IS EXPECTED FROM LATE SATURDAY
MORNING INTO EARLY SUNDAY, FOLLOWED BY ANOTHER ARCTIC BLAST
AND LOCALLY HEAVY LAKE EFFECT AND UPSLOPE SNOW ACROSS NW PA.
* WIND WILL BECOME GUSTY ON SUNDAY LEADING TO POTENTIALLY
DANGEROUS WINDCHILLS WHEN COMBINED WITH THE COLD AIR.
* SIGNS OF A WARMER PATTERN CHANGE ON THE HORIZON BY THE MIDDLE
OF NEXT WEEK.
NEAR TERM /UNTIL 8 AM SATURDAY MORNING/
MAINLY CLEAR SKIES ARE PRESENT OVER CENTRAL PENNSYLVANIA AS OF 9
PM THIS EVENING. WINDS HAVE SLACKENED AND BECOME MOSTLY CALM
AFTER THE GUSTS FROM EARLIER TODAY. HIGH PRESSURE WILL SLOWLY
WEAKEN AND HIGH CLOUDS WILL BUILD IN FROM THE WEST AHEAD OF A
CLIPPER SYSTEM PROGRESSING OVER THE CENTRAL US. CONDITIONS WILL
STAY MAINLY DRY TONIGHT, BUT NORTHWESTERLY FLOW AHEAD OF THE
SYSTEM COULD BRING A FEW LAKE EFFECT SNOW SHOWERS ACROSS THE
NORTHWEST BY DAYBREAK. LOWS TONIGHT WILL RANGE FROM THE LOW
TEENS ACROSS THE NORTH TO THE UPPER 20S IN THE SOUTHEAST.
SHORT TERM /8 AM SATURDAY MORNING THROUGH MONDAY/
THE AFOREMENTIONED CLIPPER SYSTEM WILL ARRIVE SATURDAY
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 JET DYNAMICS MOVING WITH
THIS TROUGH. THE DEEP TROUGH AND STRONG FORCING 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 /02Z SATURDAY THROUGH WEDNESDAY/
MVFR CLOUDS RE-ESTABLISHED OVER WRN AND CENT MTNS, BUT HAVE
BEGUN TO RECEDE FROM THE EAST IN PAST 2HRS. WIND SHOULD BE
GETTING LIGHTER THROUGH THE AFTN AND EVENING, AND NEARLY CALM
OVERNIGHT. WIND WILL INCREASE SLIGHTLY ON SAT. CLOUDS WILL
THICKEN UP FROM THE WEST EARLY IN THE AM, WITH LIGHT TO MDT
SNOW HITTING THE GROUND IN THE WESTERN HIGHLANDS (ESP JST)
BEFORE NOON LOCAL/17Z. L/IFR IN SN WILL SPREAD EAST AND AFFECT
ALL OF THE AREA SAT AFTN AND NIGHT, BUT END IN IPT/AOO/UNV FIRST
(BY MIDNIGHT LOCAL (05Z). JST WILL BE LIFR FOR A 3-6HR PERIOD AS
THEY SHOULD HAVE THE STEADIEST SNOW OF ANY OF OUR TERMINALS FOR
THE LONGEST TIME SAT AFTN/EVENING. IFR MAY (50%) LINGER CLOSER
TO SUNRISE IN THE SE (MDT/LNS) WITH THE WORST CONDITIONS THERE
BETWEEN 04Z-09Z. LNS WILL LIKELY BE WORSE THAN MDT WITH THE
HEAVIEST SNOW FALLING TO OUR SE (PHILLY/DC). IT WILL GET WINDY
ON SUN AND INTO EARLY SUN NIGHT AS VERY COLD AIR MOVES IN. THE
WESTERN TERMINALS (BFD AND JST MAY (40%) HAVE A FEW HOUR BREAK
SUN AM 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 SATURDAY TO 7 AM EST
MONDAY FOR PAZ004-005.
WINTER WEATHER ADVISORY FROM 10 AM SATURDAY TO 7 AM EST MONDAY
FOR PAZ010-017-024-033.
SYNOPSIS...BOWEN
NEAR TERM...BOWEN
SHORT TERM...LAMBERT/BOWEN
LONG TERM...MARTIN/NPB
AVIATION...DANGELO
CLIMATE...STEINBUGL
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