514
FXUS61 KCTP 201952
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
252 PM EST FRI DEC 20 2024
SYNOPSIS
LIGHT SNOW ACCUMULATION MAY RESULT IN SLIPPERY ROAD CONDITIONS
AND TRAVEL DISRUPTIONS INTO TONIGHT. WINDY AND MUCH COLDER
CONDITIONS ARRIVE TONIGHT AND SATURDAY, WITH COLD WEATHER
LASTING THROUGH SUNDAY AND MONDAY, FOLLOWED BY A GRADUAL WARMUP
THROUGH CHRISTMAS DAY
NEAR TERM /THROUGH TONIGHT/
NO REAL SURPRISES SO FAR WITH THE LIGHT SNOWFALL ASSOCIATED WITH
A VIGOROUS ALBERTA CLIPPER DIVING WELL SOUTHWEST OF THE REGION.
LIGHT TO LOCALLY MODERATE SNOWFALL BLOSSOMED ACROSS CENTRAL PA
THIS MORNING AHEAD OF THE ADVANCING 5H TROUGH DIGGING ESE INTO
OHIO AND WESTERN PA, WITH WIDESPREAD 1-2" ACCUMS EXTENDING FROM
THE ALLEGHENIES TO THE NORTHERN TIER, WITH LOCALLY HIGHER
AMOUNTS EXPECTED OVER THE NORTHERN TIER AND PORTIONS OF THE
MIDDLE SUSQ. THE WAA IS SHUTTING OFF OVER CENTRAL PA, BUT
REGIONAL RADAR MOSAIC AND SATELLITE IMAGERY INDICATE STRONG
CONVERGENCE IN THE DEFORMATION OVER EASTERN PA THAT WILL YIELD
SEVERAL MORE HOURS OF LIGHT AND POTENTIALLY A PERIOD OF MODERATE
SNOW LATE THIS AFTERNOON AND EVENING OVER FAR SOUTHEAST PA.
MAIN CHANGES TO FORECAST WERE TO REMOVE ANY RAIN/SNOW MIX FROM
THE LOWER SUSQ AS BOUNDARY LAYER TEMPS, OBVSERATIONS AND MODEL
FORECAST SOUNDINGS INDICATE ALL SNOW. GIVEN MARGINAL AIR TEMPS
THIS SHOULDN'T SUBSTANTIALLY CHANGE ACCUMS, BUT DID ADJUST
ACCUMS UPWARD BY A FEW TO SEVERAL TENTHS TO ACCOUNT FOR THIS AND
MORESO FOR THE CONVERGENCE THAT'S ALREADY STARTING TO BE SEEN IN
THE DEFORMATION ZONE OVER SOUTHEAST PA. MOST ROADS OVER SOUTHERN
AND SOUTHEASTERN PA ARE LIKELY TO REMAIN WET, BUT AN UPTICK IN
RATES WITH THIS CONVERGENCE IS POSSIBLE LATE THIS AFTERNOON AND
EVENING, AND HAS BEEN MESSAGED TO OUR PARTNERS.
FOCUS HEADING INTO THE EVENING AND OVERNIGHT WILL CONTINUE TO BE
ON THE AFOREMTIONED DEFORMATION THAT MAY SUPPORT A SLOWLY
PIVOTING BAND OF STEADIER SNOW GRADUALLY SINKING SOUTHWARD
ACROSS MAINLY EASTERN PORTIONS OF THE FORECAST AREA INTO EARLY
SATURDAY MORNING. THE HIGHER TERRAIN IN SULLIVAN AND NORTHERN
SCHUYLKILL COUNTIES ARE A CONCERN AND MOST LIKELY AREAS TO PICK
UP ANOTHER 1-2" BETWEEN 00-12Z SAT. WE WOULD ALSO NOT BE
SURPRISED IF THE LOWER SUSQ VALLEY PICKS UP ANOTHER 0.5"+ IF
THIS PIVOTING BAND ISN'T TOO FAR EAST. THE LATEST HRRR SUGGESTS
LIGHT SNOW COULD CONTINUE FOR MOST OF THE NIGHT BEFORE TAPERING
OFF FROM NW TO SE BEHIND PUSH OF MUCH COLDER/DRIER ARCTIC AIR
POISED TO SURGE INTO THE AREA FOR THE WEEKEND.
INCREASINGLY COLDER NWLY UPSLOPE FLOW ON THE BACKSIDE OF THE
SYSTEM MAY ALSO ENHANCE SNOW TOTALS OVER THE LAUREL HIGHLANDS
LATER TONIGHT INTO SATURDAY AS HURON CONNECTION BECOMES
ESTABLISHED.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
NO CHANGES IN THINKING FOR THE REMAINDER OF THE WEEKEND AS
SHARPLY COLDER AIR RETURNS WITH A BRISK NW WIND DRIVING WIND
CHILLS INTO THE SINGLE DIGITS AND TEENS ON SATURDAY. LAKE
EFFECT SNOW SHOWERS AND FLURRIES WILL PERSIST INTO SATURDAY
NIGHT, BUT ALL INDICATIONS ARE FOR SUB-ADVISORY AMOUNTS IN THE
USUAL SPOTS WEST AND NORTH. HOWEVER, A HURON CONNECTION APPEARS
LIKLEY WITH NNW TO SSE-ORIENTED SNOW BANDS DEVELOPING OVER THE
WESTERN MTNS, AND SOME OF THOSE AREAS COULD RECEIVE AN
ADDITIONAL INCH OR TWO WITH CAMS TARGETING SOUTHERN SOMERSET
COUNTY.
HIGHS ON SATURDAY WILL BE 10 TO 15 DEGREES BELOW THE HISTORICAL
AVERAGE WITH MAX TEMPS IN THE 20-30F RANGE. A BRISK AND GUSTY
NW WIND WILL MAKE IT FEEL LIKE THE SINGLE DIGITS/TEENS TO
AROUND 20F. SATURDAY NIGHT WILL BE QUITE COLD WITH MIN TEMPS IN
THE +SINGLE DIGITS TO UPPER TEENS WITH MINIMUM WIND CHILLS FROM
-10F TO +10F INTO EARLY SUNDAY MORNING.
MODEL GUIDANCE CONTINUES TO INDICATE NORTHWESTERLY FLOW SUNDAY
MORNING, WITH THE HIGHEST CHANCES OF LINGERING LAKE EFFECT SNOW
SHOWERS ACROSS NW PA DURING THE PRE-DAWN HOURS. NORTHWESTERLY
FLOW WILL CONTINUE TO PROMOTE CHANCES THROUGH THE LATE MORNING
HOURS ON SUNDAY BEFORE CHANCES DECREASE. ANOTHER ASPECT OF THE
FORECAST ON SUNDAY WILL BE SEASONABLY COOL TEMPERATURES WITH
BREEZY WINDS THAT WILL PROMOTE SUB-ZERO WIND CHILLS ACROSS
NORTHEASTERN PORTIONS OF THE AREA AT SUNRISE SUNDAY MORNING.
LONG TERM /MONDAY THROUGH FRIDAY/
MODEL CONSENSUS INDICATES SURFACE HIGH PRESSURE DRIFTING OFF
THE EAST COAST MONDAY, SUPPORTING GENERALLY CLEAR SKIES ON
SUNDAY THROUGH THE FIRST HALF OF MONDAY.
STRONG RADIATION COOLING UNDER CLEAR SKIES AND WEAK GRADIENT
WILL LEAD TO THE COLDEST TEMPS OF THIS OUTBREAK WITH DAYBREAK
READINGS ON MONDAY WITHIN A FEW DEG F EITHER SIDE OF ZERO ACROSS
THE NORTH AND 5-10F ACROSS MUCH OF CENTRAL AND SOUTHERN PA.
WIND CHILLS WILL BE LESS OF A CONCERN MONDAY MORNING WITH JUST A
LIGHT NORTH TO EASTERLY BREEZE AT LESS THAN 5 MPH.
LOW-MID LEVEL WARM ADVECTION FROM THE WEST MONDAY LEADS TO AN
AREA OF GENERALLY NON-PRECIPITATING MID CLOUDS SPREADING ACROSS
PENNSYLVANIA FOLLOWING BY LOWERING CLOUD BASES AND SOME LIGHT
SNOW LATE MONDAY INTO TUESDAY AS A FAIRLY FAST MOVING, NORTHERN
STREAM SHORTWAVE CROSSES PA. BEST CHANCE FOR -SN AND A LIGHT
ACCUM OF A COATING TO 2 INCHES WILL BE ACROSS THE NORTHERN MTNS
OF THE STATE.
GFS AND ITS ENSEMBLES ARE FURTHER NORTH WITH THE TRACK OF THE
MID AND UPPER LEVEL TROUGH, BUT QPF ALONG THE TRAILING COLD
FRONT LEADS TO A SIMILAR OUTCOME TO THE EC WITH RESPECT TO SNOW
PROBS/AMOUNTS.
DAY TO DAY MAX TEMP RISES FROM SUNDAY TO TUESDAY WILL BE ABOUT 7
DEG F.
MORE OF A BLOCKY/SPLIT FLOW PATTERN DEVELOPS ACROSS THE ENTIRE
CONUS AS WE HEAD THROUGH CHRISTMAS EVE AND CHRISTMAS DAY. MODELS
TO INDICATE A GENERAL DRY AND CHILLY CHRISTMAS DAY WITH MAX TEMPS
RANGING FROM THE LOW TO MID 30S NE TO THE LOW 40S IN THE
METRO AREAS OF SOUTHERN PA.
A STALLED OUT FRONTAL BOUNDARY TO OUR SOUTH COULD LIFT INTO
SOUTHERN PA AND BRING A LOW PROBABILITY FOR A LIGHT WINTRY MIX
LATER CHRISTMAS DAY INTO THURSDAY.
THE MAIN CHANGE FROM THE PREVIOUS FORECAST PACKAGES WAS TO TRIM
POPS BY ABOUT 20 PERCENT ACROSS THE BOARD WHERE MODELS SHOW A
FAIRLY EXPANSIVE SFC HIGH FROM NRN NEW ENGLAND TO THE CENTRAL
APPALACHIANS.
AVIATION /20Z FRIDAY THROUGH WEDNESDAY/
PERIODS OF LIGHT SNOW WITH WIDESPREAD IFR TO LOW END MVFR
CONDITIONS TO CONTINUE THROUGH THIS EVENING WITH SLOW
IMPROVEMENT AS WE HEAD INTO EARLY SATURDAY.
CONDITIONS FOR MOST SITES AFTER 05Z SATURDAY WILL BE
BORDERLINE MVFR. A FEW LINGERING SNOW SHOWERS ARE POSSIBLE,
ESPECIALLY AT BFD WHERE SOME LAKE EFFECT SNOW COULD OCCUR.
VFR CONDITIONS WILL BE LIKELY ACROSS THE CENTRAL RIDGE AND
VALLEY REGION AFTER 11Z SAT, WHILE PA WESTERN MTN AIRFIELDS
SHOULD STAY MVFR TO HIGH END IFR IN OCCASIONAL SNOW SHOWERS IN
BANDS STREAMING SE OFF THE GREAT LAKES.
OUTLOOK...
SAT...LINGERING SHSN NW/SW PA; GUSTY WINDS ~25-30KTS ACROSS THE
HIGHER ELEVATIONS DURING THE LATE AM/PM HOURS.
SUN...SHSN FAR NW PA; OTHERWISE, NO SIG WX.
MON...NO SIG WX.
TUE...SNOW ENTERS W PA AM, OVERSPREADS AREA BY AFTERNOON.
CLIMATE
ASTRONOMICAL WINTER (SOLSTICE) BEGINS ON SATURDAY, DECEMBER 21ST
AT 4:19 A.M. EST.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...DEVOIR/STEINBUGL
NEAR TERM...DEVOIR/STEINBUGL
SHORT TERM...DEVOIR/STEINBUGL
LONG TERM...LAMBERT/NPB
AVIATION...LAMBERT/NPB/BOWEN
CLIMATE...STEINBUGL
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