815
FXUS61 KCTP 171107
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
607 AM EST FRI JAN 17 2025
SYNOPSIS
AREAS OF GENERALLY LIGHT SNOW WILL CONTINUE ACROSS PORTIONS OF
CENTRAL PA TONIGHT, TAPERING OFF TOWARD DAYBREAK AS A POTENT
SHORTWAVE TROUGH MOVES OUT OF THE REGION. HIGH PRESSURE WILL
BUILD IN ON FRIDAY, THEN A COLD FRONT WILL PUSH THROUGH THE
STATE LATE SATURDAY WITH A PERIOD OF SNOW AND RAIN. A DEEP UPPER
LEVEL TROUGH WILL PIVOT EASTWARD INTO PENNSYLVANIA SUNDAY,
BRINGING ANOTHER CHANCE FOR SNOW ACROSS AT LEAST THE EASTERN
HALF OF PA, FOLLOWED BY DANGEROUS COLD FOR SEVERAL DAYS NEXT
WEEK.
NEAR TERM /THROUGH TONIGHT/
WITH THE SHORTWAVE TROUGH AXIS NOW EAST OF PA, MUCH OF THE
LARGER SCALE FORCING FOR THE SNOW LAST EVENING IS WANING. WITH
ONLY LIGHT FLURRIES REMAINING, WE WERE ABLE TO END THE WSW 2
HOURS AHEAD OF SCHEDULE AT 5 AM.
LAKE EFFECT (NW MTNS) AND OROGRAPHIC SNOW (LAURELS) WILL END
QUITE QUICKLY BY NOON FRIDAY AS A SFC RIDGE BUILDS OVERHEAD AND
THE SUBSIDENCE INVERSION CRASHES TO 3KFT AGL, AND LOWER IN THE
AFTERNOON.
CLEARING TO THE SE OF THE MTNS WILL HELP TEMPS CLIMB TO NEAR
40F FOR A HIGH FRIDAY AFTERNOON, BUT READINGS WILL BE CAPPED OFF
IN THE UPPER 20S TO NEAR 30 OVER THE NW MTNS (WITHIN 3F EITHER
SIDE OF DAILY NORMALS). ANY LINGERING LES SNOW BANDS SHOULD LIFT
N OF THE NY STATE LINE BY EARLY AFTN, AND EVEN SOME SUNSHINE IS
LIKELY ACROSS THE LAUREL HIGHLANDS AND NW MTNS DURING THE MID
TO LATE AFTERNOON AS THE STRATOCU DISSIPATES PRIOR TO THE HIGHER
CLOUD COVER IN ADVANCE OF THE NEXT WEATHER MAKER THICKENING UP.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
SATURDAY WILL FEATURE (RELATIVELY) MILD TEMPERATURES AS A COLD
FRONT CROSSES THE COMMONWEALTH, ACCOMPANIED BY LIGHT SNOW ACROSS
THE NORTHERN TIER AND SNOW MIXING WITH OR TRANSITIONING TO RAIN
(OR EVEN SOME POCKETS OF FREEZING RAIN) ELSEWHERE. HIGHS WILL
RANGE FROM THE LOW TO MID 30S ACROSS THE NORTHERN MOUNTAINS TO
THE LOW 40S SOUTHEAST OF THE MOUNTAINS.
THE FRONT WILL PULL TO OUR EAST SATURDAY NIGHT INTO SUNDAY,
ALTHOUGH ITS FORWARD PROGRESS WILL SLOW. COLDER AIR WILL BEGIN
TO FILTER INTO THE REGION SATURDAY NIGHT INTO SUNDAY AS WELL.
CONFIDENCE IS INCREASING IN A PERIOD OF ACCUMULATING SNOW ACROSS
THE SOUTH AND EAST SUNDAY AS A WAVE OF LOW PRESSURE DEVELOPS
ALONG THE THERMAL BOUNDARY ALONG THE NORTH CAROLINA COASTLINE.
GIVEN HOW BROAD THE TROUGH IS, THERE IS ABOVE NORMAL UNCERTAINTY
IN THE EXACT PLACEMENT OF THE AXIS OF HEAVIEST SNOW, BUT AS OF
RIGHT NOW MODEL CONSENSUS IS FOR 2-4 INCHES OF SNOW ACCUMULATION
ACROSS THE SOUTHERN TIER AND THE LOWER SUSQ VALLEY ON SUNDAY. IT
SHOULD BE NOTED, HOWEVER, THAT THE REASONABLE WORST CASE
SCENARIO WOULD BE A SFC LOW DEVELOPING FASTER AND TRACKING
CLOSER TO THE MID ATLANTIC COAST, WHICH COULD BUT US IN A
POSITION WHERE THE LOWER SUSQ SEES WARNING CRITERIA TOTALS (5+
INCHES). FOR NOW, THE CHC OF WARNING CRITERIA SNOW TOTALS
REMAINS JUST BELOW 30%, AND IT IS MORE LIKELY THAT WE WOULD END
UP HOISTING A WINTER WEATHER ADVISORY IN THE COMING DAYS.
LONG TERM /MONDAY THROUGH THURSDAY/
A REINFORCING SHOT OF BITTERLY COLD AIR ARRIVES SUNDAY NIGHT
INTO MONDAY. TEMPERATURES WILL BOTTOM OUT TUESDAY, WITH HIGHS
RUNNING 20 TO 30 DEGREE BELOW AVERAGE. CONSIDERING THAT LATE
JANUARY IS THE CLIMATOLOGICAL COLDEST TIME OF THE YEAR, HIGHS
THAT FAR BELOW AVERAGE MEANS THAT WE ARE IN FOR A SIGNIFICANT
BOUT OF ARCTIC AIR.
TO PUT THE UPCOMING COLD IN HISTORICAL PERSPECTIVE, IF THE
FORECAST HOLDS, ABOUT 80 HOURS WITH TEMPERATURES IN THE MID
TEENS OR COLDER AT HARRISBURG AND WILLIAMSPORT RIVALS THE COLD
SNAP OF FEB 1996 IN TERMS OF DURATION.
THE UPPER-LEVEL TROUGH WILL BEGIN TO LIFT OUT OF THE AREA BY
LATE NEXT WEEK, WHICH SHOULD RESULT IN SLOWLY MODERATING
TEMPERATURES.
AVIATION /12Z FRIDAY THROUGH TUESDAY/
IFR/LIFR CONDITIONS AT KBFD AND KJST EXPECTED TO PERSIST INTO
MIDDAY BEFORE GRADUALLY IMPROVING TO VFR BY THE AFTERNOON. LIGHT
SNOW SHOWERS AND OCNL FREEZING DRIZZLE ARE PROBABLE EARLY THIS
MORNING THANKS TO RESIDUAL LLVL MOISTURE AND UPSLOPE FLOW.
A SIMILAR [IMPROVING] TREND IS ALSO EXPECTED AT KAOO AND KUNV
WITH MVFR CIGS LIFTING TO LOW END VFR BY 15-16Z. VFR WILL HOLD
ACROSS THE EASTERN AIRFIELDS THROUGH THE 17/06Z TAF CYCLE, WITH
WIDESPREAD VFR ANTICIPATED FOR THE MAJORITY OF THE SECOND HALF
OF THE PERIOD (18Z FRI TO 06Z SAT).
INCREASING SOUTHWEST WINDS ALOFT, COMBINED WITH RELATIVELY
LIGHT SURFACE WINDS, WILL RESULT IN LLWS FRIDAY EVENING ACROSS
NORTHWEST PA. THEREFORE, WE ADDED LLWS TO THE BFD TAF AFTER 00Z
SAT.
OUTLOOK...
SAT...LLWS NW MTNS EARLY. LIGHT SNOW AND IFR CIGS LIKELY,
MAINLY N AND W MTNS. RAIN/SNOW MIX AND EVENING FOG POSSIBLE
SOUTHEAST PA.
SUN...AM LOW CIGS W MTNS AND SOUTHEAST PA. SNOW/IFR CONDITIONS
INCREASINGLY LIKELY FOR AT LEAST THE SOUTHEAST 1/2 OF THE AREA
SUNDAY PM.
MON...MVFR TO IFR IN SNOW SHOWERS ACROSS WESTERN PA.
TUE...NO SIG WX EXPECTED.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...LAMBERT/COLBERT
NEAR TERM...LAMBERT/COLBERT
SHORT TERM...LAMBERT/COLBERT
LONG TERM...FITZGERALD/EVANEGO/COLBERT
AVIATION...FITZGERALD/STEINBUGL
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