211
FXUS61 KCTP 171713
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1213 PM EST FRI JAN 17 2025
SYNOPSIS
HIGH PRESSURE WILL BUILD ACROSS THE AREA TODAY WITH A BRIEF
PERIOD OF DRY CONDITIONS WITH DECREASING CLOUDS THIS AFTERNOON
AND EVENING. 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/
SFC RIDGE AXIS IS MOVING ACROSS THE SUSQ VALLEY ACCOMPANIED BY A
PECULIAR, SHARP/SMALL CIRCULAR AREA OF CLEARING (ABOUT 30-40 NM
IN DIAMETER) MOVING SE ACROSS THE MDT, MUI AND LNS AREAS LATE
THIS MORNING. THE ORIGINAL MECHANISM THAT CAUSED THIS
ORIGINATED ACROSS THE NCENT MTNS BEFORE DAYBREAK AND PROGRESSED
SE TO WHERE IT IS NOW. PERHAPS AN SMALL POCKET OF ANOMALOUSLY
LOW PWAT AIR ACCENTUATED BY LLVL STREAMLINE
DIVERGENCE/SUBSIDENCE AND DOWNSLOPING OFF TERRAIN.
EXPECT TO SEE SOME PARTIAL EROSION OF THE SHALLOW/WARMING
STRATOCU DECK THIS AFTERNOON AND LIKELY SEVERAL HOURS OF
CLEARING LATER THIS AFTERNOON AND EVENING AS THE WESTERN EDGE OF
THE CLOUD LAYER (NOW JUST EAST OF THE PA/OHIO BORDER) IS MOVING
NE AT 25-30 KTS.
CLEARING FIRST TO THE SE OF THE MTNS WILL HELP TEMPS CLIMB TO
NEAR 40F FOR A HIGH THIS AFTERNOON, BUT READINGS WILL BE CAPPED
OFF IN THE UPPER 20S TO NEAR 30F OVER THE NW MTNS (WITHIN 3F
EITHER SIDE OF DAILY NORMALS).
SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/
CLOUDS WILL THICKEN-UP OVERNIGHT AND 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.
LONG TERM /SUNDAY THROUGH THURSDAY/
LATE MORNING UPDATE.
UPDATED THE GRIDS AS OF LATE MORNING.
EARLIER INFORMATION BELOW.
SUNDAY...
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.
SUNDAY NIGHT INTO LATE WEEK.
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. SEVERAL YEARS IN THE
1970S FEATURED LONG DURATION COLD AS WELL.
THE UPPER-LEVEL TROUGH WILL BEGIN TO LIFT OUT OF THE AREA BY
LATE NEXT WEEK, WHICH SHOULD RESULT IN SLOWLY MODERATING
TEMPERATURES.
AVIATION /18Z FRIDAY THROUGH WEDNESDAY/
A GRADUAL IMPROVING TREND WILL OCCUR ACROSS THE REGION THIS
AFTERNOON (WITH LOCATIONS ACROSS THE CENTRAL AND WESTERN MTNS
THAT WERE STILL MVFR EXPECTED TO BECOME VFR BY 21Z).
VFR WILL EXTEND THROUGH THE OVERNIGHT HOURS.
LLWS WILL BECOME A FACTOR LATER TONIGHT INTO SAT MORNING,
MAINLY ACROSS OUR WESTERN MTNS AIRFIELDS (KJST TO KBFD) AS A
RESULT OF INCREASING SOUTHWEST WINDS ALOFT, COMBINED WITH
RELATIVELY LIGHT SURFACE WINDS.
WE HAVE LLWS TO THESE TAFS BETWEEN 00-06Z SAT.
OUTLOOK...
SAT...LLWS WEST EARLY. LIGHT SNOW AND MVFR TO IFR CIGS EXPECTED.
RAIN/SNOW MIX AND EVENING FOG POSSIBLE IN SOUTHEAST PA.
SUN...AM LOW CIGS W MTNS AND SOUTHEAST PA. SNOW/IFR CONDITIONS
INCREASINGLY LIKELY FOR AT LEAST THE SOUTHERN AND SOUTHEASTERN
1/2 TO 1/3 OF THE AREA SUNDAY PM.
MON...MVFR TO IFR IN SNOW SHOWERS ACROSS WESTERN PA.
TUE...NO SIG WX EXPECTED; VERY COLD.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...LAMBERT
NEAR TERM...LAMBERT
SHORT TERM...LAMBERT/COLBERT
LONG TERM...FITZGERALD/MARTIN/EVANEGO/COLBERT
AVIATION...LAMBERT/STEINBUGL
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