111
FXUS61 KCTP 170105
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
805 PM EST THU JAN 16 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 FRIDAY/
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 /FRIDAY NIGHT/
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 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. 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.
COLDER AIR WILL BEGIN TO FILTER INTO THE REGION SATURDAY NIGHT
INTO SUNDAY AS WELL, WITH A REINFORCING SHOT OF BITTERLY COLD
AIR ARRIVING 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 /01Z FRIDAY THROUGH TUESDAY/
THE MAIN AVIATION CONCERN OVERNIGHT WILL BE ACROSS THE W MTNS,
WHERE RESIDUAL MOISTURE BEHIND EXITING LOW PRESSURE WILL PRODUCE
LOW CIGS AND LINGERING LIGHT SNOW. UPSTREAM OBSERVATIONS AND
MODEL SOUNDINGS SUPPORT PREDOMINANTLY IFR CONDITIONS FROM KBFD
SOUTH THROUGH KJST OVERNIGHT.
ELSEWHERE, LIGHT SNOW OVER THE EASTERN HALF OF PA WILL TAPER
OFF THIS EVENING, AS AN ASSOCIATED WEAK LOW PRESSURE SYSTEM
PASSES OFF OF THE DELMARVA PENINSULA. RADAR TRENDS INDICATE
TEMPO MVFR CONDITIONS CAN BE EXPECTED FROM KIPT SOUTH THROUGH
KMDT/KLNS UNTIL AROUND 04Z, WITH A HIGH CONFIDENCE IN VFR
THEREAFTER. FURTHER WEST, MODEL SOUNDINGS INDICATE LINGERING
MVFR CIGS ARE LIKELY AT KUNV/KAOO THROUGH THE NIGHT.
A RIDGE OF HIGH PRESSURE BUILDING INTO PA FROM THE OHIO VALLEY
WILL BRING IMPROVING FLYING CONDITIONS FRIDAY, WITH LIGHT WINDS
ACROSS THE ENTIRE REGION. FORECAST SOUNDINGS INDICATE CIGS
ACROSS THE W MTNS SHOULD LIFT TO MVFR BY AROUND 15Z FOLLOWED BY BREAKING
CLOUDS LATE IN THE DAY. IMPROVEMENT SHOULD ARRIVE EARLIER
DOWNWIND (EAST) OF THE ALLEGHENIES, WITH WIDESPREAD VFR
ANTICIPATED BY 16Z.
INCREASING SOUTHWEST WINDS ALOFT, COMBINED WITH RELATIVELY LIGHT
SURFACE WINDS, COULD POTENTIALLY RESULT IN LLWS CRITERIA FRIDAY
EVENING ACROSS THE NW MTNS (KBFD).
OUTLOOK...
SAT...LIGHT SNOW/LOW CIGS LIKELY, MAINLY N AND W MTNS. EVENING
FOG POSSIBLE SOUTHEAST PA. EARLY AM LLWS ALSO POSSIBLE, MAINLY
NW MTNS.
SUN...AM LOW CIGS POSSIBLE W MTNS AND SOUTHEAST PA. SNOW
POSSIBLE SOUTHERN PA LATER IN THE DAY.
MON...LIGHT SNOW/VIS REDUCTIONS POSSIBLE W MTNS, MAINLY AM.
TUE...NO SIG WX EXPECTED.
CTP WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 7 AM EST FRIDAY FOR PAZ004-005-
010-017-024.
WINTER STORM WARNING UNTIL 7 AM EST FRIDAY FOR PAZ033.
SYNOPSIS...LAMBERT/COLBERT
NEAR TERM...LAMBERT/COLBERT
SHORT TERM...LAMBERT/COLBERT
LONG TERM...FITZGERALD/EVANEGO/COLBERT
AVIATION...FITZGERALD
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