270
FXUS61 KCTP 170630
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
130 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 TODAY/
WITH THE SHORTWAVE TROUGH AXIS NOW EAST OF PA, MUCH OF THE
LARGER SCALE FORCING FOR THE SNOW EARLIER TODAY IS WANING. A
VORT MAX ON THE BACK SIDE OF THE TROUGH WILL TRANSLATE SE FROM
LAKE ERIE ACROSS CENTRAL PA THROUGH 06Z MAINTAINING SNOW MAINLY
ACROSS THE FAVORED UPSLOPE REGION OF THE LAUREL HIGHLANDS, AS
WELL AS LAKE EFFECT SNOW IN THE NW MOUNTAINS, WHERE UP TO AN
ADDITIONAL 2 INCHES OF SNOW IS POSSIBLE THROUGH DAYBREAK FRI.
NEAR NEUTRAL LLVL TEMP ADVECTION FROM THE WEST AND PLENTY OF
CLOUD COVER THRU MOST OF THE NIGHT TONIGHT WILL LIMIT TEMPS FROM
FALLING BELOW THE UPPER TEENS NE, AND M20S IN THE SOUTH-
CENTRAL MTNS (0-10F ABOVE NORMALS).
SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/
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.
LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/
THE EXTENDED PERIOD WILL BEGIN WITH AN UPPER LEVEL RIDGE
PUSHING OFF THE EAST COAST. THE RIDGE WILL BE REPLACED BY UPPER
LEVEL TROUGHING THAT WILL PERSIST OVER THE EASTERN UNITED STATES
THROUGH AT LEAST THE MIDDLE OF NEXT WEEK.
SATURDAY WILL FEATURE (RELATIVELY) MILD TEMPERATURES AS A COLD
FRONT CROSSES THE COMMONWEALTH, ACCOMPANIED BY LIGHT SNOW
ACROSS NORTHERN PA AND LIGHT RAIN OR SNOW (OR EVEN A BIT OF
FREEZING RAIN) ACROSS THE SOUTH. 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.
WE WILL HAVE TO WATCH FOR THE POTENTIAL FOR AN AREA OF LOW
PRESSURE TO DEVELOP OFF THE CAROLINA COAST AND PUSH SOME LIGHT
SNOW NORTHWARD INTO SOUTHEASTERN PENNSYLVANIA ON SUNDAY. AT THIS
TIME, MODEL CONSENSUS IS FOR 1-3 INCHES OF SNOW ACCUMULATION
THROUGH THE LOWER SUSQ VALLEY ON SUNDAY.
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. FOR STATE COLLEGE, 3 DAYS
WITH HIGHS OF 12F OR LOWER ONLY HAPPENED ONCE IN THE PAST 100
YRS, IN FEB 1971. IT DID ALSO HAPPEN A FEW TIMES IN THE 1800S.
THE UPPER-LEVEL TROUGH WILL BEGIN TO LIFT OUT OF THE AREA BY
LATE NEXT WEEK, WHICH SHOULD RESULT IN SLOWLY MODERATING
TEMPERATURES.
AVIATION /06Z 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
WINTER WEATHER ADVISORY UNTIL 7 AM EST THIS MORNING FOR PAZ004-
005-010-017-024.
WINTER STORM WARNING UNTIL 7 AM EST THIS MORNING FOR PAZ033.
SYNOPSIS...LAMBERT/COLBERT
NEAR TERM...LAMBERT/COLBERT
SHORT TERM...LAMBERT/COLBERT
LONG TERM...FITZGERALD/EVANEGO/COLBERT
AVIATION...FITZGERALD/STEINBUGL
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