491  
FXUS61 KCTP 201151  
AFDCTP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE STATE COLLEGE PA  
651 AM EST FRI DEC 20 2024  
   
SYNOPSIS
 
 
* LIGHT SNOW ACCUMULATION MAY RESULT IN SLIPPERY ROAD CONDITIONS  
AND TRAVEL DISRUPTIONS TODAY AND TONIGHT  
* BRISK AND MUCH COLDER THIS WEEKEND WITH SNOW SHOWERS SATURDAY  
AND FRIGID WIND CHILLS SATURDAY NIGHT INTO EARLY SUNDAY  
* SEASONABLY COLD START NEXT WEEK FOLLOWED BY A GRADUAL WARMUP  
THROUGH CHRISTMAS DAY  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
WEAKENING 1014MB CLIPPER SYSTEM ANALYZED OVER NORTHERN INDIANA  
AT 08Z WILL YIELD TO AN AREA OF LOW PRESSURE ORGANIZING ALONG A  
STRENGTHENING FRONTAL BOUNDARY OFF THE CAROLINA COAST. BROAD  
UPPER LEVEL DIVERGENCE OUT AHEAD OF THE 250-500MB MEAN TROUGH  
AXIS WILL SUPPLY SUFFICIENT ASCENT ALOFT IN TANDEM WITH THE  
RESIDUAL MOISTURE AND LLVL WAA FROM THE CLIPPER SYSTEM TO  
SUPPORT A "BURST" OF SNOW OVER CENTRAL PA BETWEEN 12-18Z. HIRES  
ENSEMBLE DATA SHOWS A GRADUAL RAMP IN HOURLY SNOWFALL RATES  
DURING THIS TIMEFRAME PEAKING IN THE 0.50-0.75" RANGE AS SNOW  
SPREADS FROM WEST TO EAST. BLEND OF NBM/WPC/HREF DATA INDICATES  
A GENERAL 1-3" ACCUMULATION NEAR AND NORTH OF I80 (HIGHEST ON  
THE RIDGETOPS) WITH A COATING-1" FCST ACROSS THE LAUREL  
HIGHLANDS AND MOST OF SOUTH CENTRAL PA (LOWEST AMOUNTS 0-0.5" IN  
THE LOWER SUSQ VALLEY WHERE SOME RAIN/SNOW MIX IS POSSIBLE).  
 
TIMING OF THE LIGHT TO MODERATE SNOW IS A BIT OF A CONCERN  
IMPACT-WISE, AND WILL LIKELY ISSUE A SPS TO DRAW AWARENESS TO  
POTENTIAL FOR SLIPPERY ROAD CONDITIONS AND TRAVEL DISRUPTIONS.  
MARGINAL AIR/ROAD TEMPERATURES SUGGEST BULK OF ACCUMULATION MAY  
BE ON THE GRASS OR NON-PAVED SURFACES WITH ELEVATION DEPENDENCE  
PARTICULARLY NEAR AND TO THE EAST OF I99/I80 CORRIDOR. ROADS ARE  
MOST LIKELY TO BE JUST WET ACROSS THE MAJORITY OF THE LOWER  
SUSQUEHANNA VALLEY.  
 
FOCUS HEADING INTO THE EVENING AND OVERNIGHT WILL BE ON A  
CONVERGENCE BOUNDARY THAT CAMS ARE KEYING ON -- PROGGED TO SETUP  
BENEATH THE LEFT EXIT REGION OF A MID/UPPER LEVEL JET STREAK.  
HIRES DATA IS TRENDING BULLISH ON A SLOWLY PIVOTING BAND OF  
DEFORMATION SNOW GRADUALLY SINKING SOUTHWARD ACROSS 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 A 0.5" OR SO IF THIS PIVOTING BAND COMES TO FRUITION. 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 SATURDAY NIGHT/
 
 
THE PATTERN TURNS BRISK AND MUCH COLDER TO START WEEKEND WITH  
LAKE EFFECT SNOW SHOWERS AND FLURRIES INTO SATURDAY NIGHT.  
MODELS SHOW A HURON CONNECTION WITH SNOW BANDS DEVELOPING OVER  
THE WESTERN MTNS. SOME PLACES 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.  
 

 
   
LONG TERM /SUNDAY THROUGH THURSDAY/
 
 
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.  
 
SURFACE HIGH PRESSURE IS PROGGED BY THE BULK OF MODEL GUIDANCE  
TO CONTINUE DRIFT OFF THE EAST COAST SUNDAY EVENING INTO MONDAY,  
PROMOTING GENERALLY CLEAR SKIES ON SUNDAY AND INTO THE FIRST  
HALF OF MONDAY. THIS WILL ALLOW FOR PEAK WARMING DURING THE  
DAYTIME HOURS AND RADIATIONAL COOLING SUNDAY EVENING INTO  
MONDAY, THUS HAVE UNDERCUT NBM MINTS IN THIS TIMEFRAME. THE  
INFLUENCE OF HIGH PRESSURE WILL KEEP WINDS LIGHTER, SO WIND  
CHILLS WILL BE LESS ON A CONCERN MONDAY MORNING.  
 
CLOUDS BEING TO INCREASE ACROSS WESTERN PENNSYLVANIA BY MIDDAY  
ON MONDAY AND INCREASING AREA WIDE THROUGH MONDAY NIGHT. THERE  
REMAINS CONSIDERABLE SPREAD IN MODEL GUIDANCE IN THE TUESDAY TO  
WEDNESDAY TIMEFRAME WITH GFS MODEL GUIDANCE OUTLINING LOW  
PRESSURE MOVING TO THE NORTH AND BRINING HIGHER SNOWFALL CHANCES  
WHILE THE ECMWF OUTLINES A WEAKER DISTURBANCE WITH SNOWFALL  
CONFINED TO THE NORTHERN TIER, MAINLY ON TUESDAY. THE MAIN  
DEVIATION FROM NBM GUIDANCE IN THIS TIMEFRAME WAS TO TRIM POPS  
ACROSS THE LOWER SUSQUEHANNA VALLEY ON WEDNESDAY MORNING, WHERE  
MODEL GUIDANCE DOES INDICATE SOME DRIER AIR POTENTIALLY LIMITING  
PRECIPITATION CHANCES. THE UNSETTLED PATTERN IS EXPECTED TO  
CONTINUE INTO THURSDAY, WITH LITTLE DEVIATION FROM NBM GUIDANCE  
DUE TO THE AFOREMENTIONED UNCERTAINTY IN MODEL GUIDANCE TOWARDS  
THE END OF THE LONG-TERM FORECAST PERIOD.  
 

 
   
AVIATION /12Z FRIDAY THROUGH TUESDAY/
 
 
SNOW SHOWERS HAVE BEGUN TO OVERSPREAD ACROSS THE CENTRAL  
PENNSYLVANIA AIRSPACE. THE WESTERN SITES OF BFD/JST/AOO HAVE  
ALREADY BEGUN TO SEE REDUCTIONS IN FLIGHT CATEGORY DUE TO LOSS  
OF VISIBILITY AND LOW CEILINGS FROM SNOW. THESE SNOW SHOWERS  
WILL BECOME MORE WIDESPREAD THROUGHOUT THE DAY. ALL SITES SHOULD  
EXPECT TO EXPERIENCE IFR OR LOWER FLIGHT CATEGORIES. TEMPO  
GROUPS HAVE BEEN INCLUDED AT JST/IPT WHERE CONFIDENCE IS  
GREATEST IN BURSTS OF HEAVIER SNOW REDUCING VISIBILITY BELOW 1  
MILE. HREF PROBABILITIES ARE ALSO OUTLINING LIFR CONDITIONS AT  
BFD WHERE CONFIDENCE IN BURSTS OF HEAVIER SNOW IS GREATEST.  
 
THERE REMAINS SOME UNCERTAINTY WITH REGARDS TO THE INITIAL FALL  
IN CEILINGS/VISIBILITIES AT MDT/LNS WITH GLAMP GUIDANCE  
OUTLINING AN INITIAL FALL TOWARDS MVFR CEILINGS BEFORE IFR  
PREVAILS 1-2 HOURS LATER WITH RAP MODEL SOUNDINGS OUTLINING A  
MORE DRASTIC FALL IN VISIBILITIES. GRADUAL IMPROVEMENT WILL BE  
EXPECTED FOR MOST SIZES AFTER 0Z SATURDAY TO BORDERLINE MVFR. A  
FEW LINGERING SNOW SHOWERS ARE POSSIBLE, ESPECIALLY AT BFD  
WHERE SOME LAKE EFFECT SNOW COULD OCCUR. VFR CONDITIONS ARE NOT  
LIKELY TO BE SEEN DURING THIS TAF PACKAGE.  
 
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...STEINBUGL  
NEAR TERM...STEINBUGL  
SHORT TERM...STEINBUGL  
LONG TERM...NPB  
AVIATION...NPB/BOWEN  
CLIMATE...STEINBUGL  
 
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