610
FXUS61 KCTP 182052
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
352 PM EST SAT JAN 18 2025
SYNOPSIS
*QUICK-HITTING, PLOWABLE TO LOCALLY HEAVY SNOWFALL ON SUNDAY
WITH HIGHEST ACCUMULATIONS ACROSS THE SOUTHEAST.
*ARCTIC BLAST AND DANGEROUSLY COLD WIND CHILLS MONDAY-WEDNESDAY
*DRY CONDITIONS LATER THIS WEEK WITH SCATTERED SNOW SHOWERS.
NEAR TERM /UNTIL 3 AM SUNDAY MORNING/
CURRENT RADAR OUTLINES DECAYING SHOWERS ACROSS MAINLY THE
NORTHERN HALF OF CENTRAL PENNSYLVANIA, WITH RAIN THE PREDOMINANT
PRECIPITATION TYPE OUTSIDE OF FAR NW PA. LOW-LEVEL DRY AIR
OBSERVED ON RECENT MODEL SOUNDINGS PROMOTE DECREASING CHANCES OF
PRECIPITATION OVER THE NEXT COUPLE OF HOURS; HOWEVER,
SOUTHWESTERLY FLOW DOES PROMOTE RETAINING CHANCES ACROSS THE
FAVORED UPSLOPE ZONES OF WESTERN PENNSYLVANIA WITH MINIMAL
ACCUMULATIONS FO RAIN/SNOW. THE BULK OF PRECIPITATION IS
EXPECTED TO TAPER OFF CLOSER TO MIDNIGHT, WITH LINGERING SHOWER
CONFINED TO THE HIGHEST ELEVATIONS OF SOMERSET COUNTY.
RECENT MODEL GUIDANCE DOES SUGGEST SOME BREAKS IN CLOUD COVER
DURING THE LATE AFTERNOON/EARLY EVENING HOURS, BUT HAVE RETAINED
SKY COVER THROUGHOUT THE NEAR-TERM WITH RECENT SATELLITE TRENDS
OUTLINING MORE CLOUD COVER COMPARED TO HI-RES MODEL GUIDANCE AS
CLOUD COVER GETS REINFORCED BY LOW-LEVEL MOISTURE STREAMING
INTO THE AREA FROM THE SOUTHWEST. WITH THE AFOREMENTIONED CLOUD
COVER, TEMPERATURES ARE NOT EXPECTED TO CLIMB MUCH MORE THIS
AFTERNOON AHEAD OF SUNSET WITH MAXTS RANGING FROM THE MID-30S
ACROSS THE HIGHER ELEVATIONS TO THE LOWER 40S ACROSS THE LOWER
SUSQUEHANNA VALLEY, TRACKING CLOSE TO 3PM EST OBSERVATIONS.
SHORT TERM /3 AM SUNDAY MORNING THROUGH MONDAY/
THE BEGINNING STAGES OF THE SHORT-TERM WILL BE HONED IN ON THE
NEXT SYSTEM, IN THE FORM OF A FORMING COASTAL LOW ALONG THE
MID-ATLANTIC COAST THAT IS EXPECTED TO BRING PLOWABLE SNOWFALL
TO EASTERN PENNSYLVANIA. FIRSTLY, ONSET OF PRECIPITATION HAS
TRENDED SLIGHTLY LATER WITH A LESS PROGRESSIVE UPPER-LEVEL JET,
THUS HAVE TRENDED BACK ONSET OF SNOWFALL CLOSER TO SUNRISE WITH
COOLING TEMPERATURES DURING THE OVERNIGHT PERIOD CONTINUING TO
OUTLINE AN "ALL-SNOW" EVENT FOR THE REGION.
FRONTOGENESIS IN THE 850-700MB LAYER HAS CONTINUED TO HIGHLIGHT
AN INCREASING POTENTIAL FOR A HEAVIER SNOWBAND, WITH SNOWFALL
RATES APPROACHING (AND POTENTIALLY EXCEEDING) ONE INCH AN HOUR
RATES ACROSS PORTIONS OF THE LOWER SUSQUEHANNA VALLEY. OF NOTE,
RECENT HREF GUIDANCE ALSO DOES OUTLINE SOME BANDING POTENTIAL
FURTHER NORTH, WITH A SECONDARY AREA OF CONCERN ACROSS
SCHUYLKILL/COLUMBIA COUNTY THAT HAS LED TO AN INCREASE IN
SNOWFALL TOTALS FOR THESE ZONES, PUSHING THEM ABOVE WARNING
CRITERIA FOR THE EVENT. WHILE SOME MODEL DISCREPANCIES WITH
RESPECT TO TIMING DO STILL EXIST (WITH CURRENT FORECAST
OUTLINING LATE MORNING TO EARLY AFTERNOON AS THE BEST TIMING FOR
SNOW BANDING), FRONTOGENETIC FORCING REMAINS CONSTANT IN
BETWEEN MODEL CYCLES, INCREASING CONFIDENCE THAT THERE WILL BE A
HEAVIER SNOWBAND WITH SOME UNCERTAINTY WITH WHERE THE BAND WILL
SET UP. A FURTHER NORTH SOLUTION WOULD PROMOTE SOME EXPANSION
OF ADVISORIES FURTHER NORTH; HOWEVER, THIS SEEMS TO BE A LOWER
CONFIDENCE SOLUTION AT THIS TIME.
AS MENTIONED, HEAVIER SNOWFALL ACROSS THE LOWER SUSQUEHANNA
VALLEY IS EXPECTED TO LEAD TO LOCALLY HIGHER ACCUMULATIONS FOR
THIS COASTAL LOW EVENT, WITH THE BEST SIGNAL FOR SNOWFALL TOTALS
EXCEEDING 5" ACROSS THE LSV AND SLIGHTLY NORTH INTO SCHUYLKILL
COUNTY (WHERE WARNING CRITERIA IS 6"). HAVE COLLABORATED WITH
WFO PHI/BGM/PBZ/LWX, AND GIVEN THESE SIGNALS, WE HAVE UPGRADED
TO A WARNING FOR THE LOWER SUSQUEHANNA VALLEY, ALONG WITH
COLUMBIA/SCHUYLKILL WHERE 6" IS INCREASINGLY LIKELY GIVEN RECENT
MODEL GUIDANCE WITH A TIER OF ADVISORIES ON THE NORTH-END AND
INTO THE LAUREL HIGHLANDS WHERE LINGERING UPSLOPE ACCUMULATIONS
COULD PUSH ACCUMULATIONS CLOSER TO THE 3-4" RANGE.
COLD, DRY AIR ENTERS BEHIND THE SYSTEM SUNDAY NIGHT, ALLOWING
FOR A QUICK DRYING TREND IN PRECIPITATION WITH COLDER
TEMPERATURES BEGINNING TO TAKE HOLD OVER THE REGION, WITH MINTS
INTO MONDAY MORNING RANGING FROM THE SINGLE DIGITS ACROSS THE
LAURELS TO NEAR 15 DEGREES ACROSS THE LOWER SUSQUEHANNA VALLEY.
WINDS WILL BEGIN TO BECOME BREEZY TO GUSTY LATE SUNDAY EVENING
INTO MONDAY MORNING, WHICH COUPLED WITH THE AFOREMENTIONED COLD
TEMPERATURES ALLOWING FOR WIND CHILLS TO RANGE FROM THE -10/-15F
RANGE TO THE LOWER SINGLE DIGITS ACROSS THE LOWER SUSQUEHANNA
VALLEY. THIS CYCLE, HAVE DECIDED TO RIDE THE EXTREME COLD WATCH
GIVEN SOME MARGINALITY IN TEMPERATURES; HOWEVER, SOMERSET AND
CAMBRIA COUNTIES WILL BE THE FIRST COUNTIES IN CONSIDERATION FOR
EXTREME COLD WARNINGS, BUT CONFIDENCE REMAINS TOO LOW AT THIS
TIME.
LONG TERM /MONDAY NIGHT THROUGH SATURDAY/
NOT A LOT OF CHANGE TO THIS SECTION.
LOOKING AT A IMPRESSIVE STRETCH OF FRIGID AIR. ONLY FACTOR
THAT HELPS IS WINDS NOT AS STRONG AS SOME EVENTS, SUCH AS
THE DECEMBER EVENT BEFORE CHRISTMAS A FEW YEARS AGO.
ALSO WINDS BACK MORE TO THE SOUTHWEST ON TUESDAY, LIMITING
ANYTHING OFF THE GREAT LAKES.
SOUTHERN SYSTEM LATE TUESDAY COULD BRUSH THE FAR SOUTH.
TEMPERATURES DO WARM TO NEAR NORMAL LATER IN THE WEEK, WITH
SMALL ROUNDS OF SNOW SHOWERS. NEXT COLD FRONT BY NEXT WEEKEND.
AN EXTREME COLD WATCH FROM 4AM MONDAY THROUGH 12PM WEDNESDAY
FOR LOCATIONS NORTH AND WEST OF THE ALLEGHENY FRONT REMAINS
IN EFFECT.
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.
AVIATION /21Z SATURDAY THROUGH THURSDAY/
A MIXED BAG OF OBSERVATIONS REMAINS WITH RESTRICTIONS AT ALL
AIRFIELDS ACROSS THE LOWER SUSQUEHANNA VALLEY (MDT/LNS) THIS
AFTERNOON. GENERALLY EXPECT IFR/MVFR CEILINGS AND VISIBILITIES
AT BFD/JST THROUGHOUT MUCH OF THE TAF PERIOD, WITH MODEL
GUIDANCE INDICATING A BRIEF WINDOW AT AOO/UNV/IPT WHERE DRIER
AIR IN THE LOWER LEVELS WILL ALLOW FOR SOME SCATTERING OUT OF
THE LOWER LEVEL CLOUD DECK NEAR 06Z SUNDAY. THIS WINDOW IS
GENERALLY EXPECTED TO RANGE FROM 2-3 HOURS WITH MODERATE (~50%)
CONFIDENCE ON TIMING, AND HIGHER CONFIDENCE (~70%) ON THE TIMING
WINDOW OF THESE VFR CONDITIONS. FURTHER SOUTHEAST, GENERALLY
EXPECT VFR CONDITIONS TO CONTINUE OUTSIDE OF THE 22Z SATURDAY TO
06Z SUNDAY WINDOW, WHERE RAP MODEL SOUNDINGS INDICATE SOME LOW-
LEVEL MOISTURE WITH SHOWERS MAKING CLOSE APPROACH TO THE
AIRFIELDS.
A COASTAL LOW WILL BRING ABOUT SNOW, ESPECIALLY ACROSS
AIRFIELDS ACROSS THE LAURELS (JST/AOO) AND SOUTHEASTERN
PENNSYLVANIA (MDT/LNS) WITH INCREASING CONFIDENCE ON IFR-TO-LIFR
CONDITIONS DURING THE LATE MORNING TO AFTERNOON HOURS (AFTER
15Z SUNDAY), ESPECIALLY ACROSS MDT/LNS. HEAVIER SNOW IS ALSO
POSSIBLE CLOSER TO IPT/UNV; HOWEVER, IMPACTS OF HEAVIER SNOW
WILL BE LIMITED TO 1-2 HOURS AND CONFIDENCE REMAINS FAIRLY LOW
COMPARED TO AIRFIELDS FURTHER SOUTH/EAST, SO HAVE PROGGED TIMING
WITH A PROB30 GROUP DUE TO SOME MODEL DISPARITY. FURTHER NW AT
BFD, HEAVIER SNOW ASSOCIATED WITH THE SURFACE LOW IS NOT
EXPECTED THROUGH 18Z SUNDAY; HOWEVER, LOW-LEVEL MOISTURE PROGGED
BY RAP SOUNDINGS AND SUPPORTED IN RECENT HREF
GUIDANCE/PROBABILITIES WARRANT IFR TO LOW-END MVFR MENTIONS
AFTER 12Z SUNDAY, WITH BEST WINDOW FOR MVFR CONDITIONS COMING IN
THE LATE MORNING HOURS.
OUTLOOK...
MON...MVFR TO IFR IN SNOW SHOWERS ACROSS WESTERN PA; GUSTY WEST
WINDS.
TUE...NO SIG WX EXPECTED; VERY COLD.
WED...SCATTERED SNOW SHOWERS POSSIBLE, BRINGING LOCALIZED
RESTRICTIONS.
THU...NO SIG WX EXPECTED; COLD.
CTP WATCHES/WARNINGS/ADVISORIES
EXTREME COLD WATCH FROM LATE SUNDAY NIGHT THROUGH WEDNESDAY
MORNING FOR PAZ004>006-010>012-017-018-024-033-037-041-042.
WINTER WEATHER ADVISORY FROM 4 AM TO 10 PM EST SUNDAY FOR
PAZ019-024>028-033>035-042-045-046-049>052.
WINTER STORM WARNING FROM 4 AM TO 10 PM EST SUNDAY FOR PAZ036-
053-056>059-063>066.
SYNOPSIS...NPB
NEAR TERM...NPB
SHORT TERM...NPB
LONG TERM...MARTIN
AVIATION...NPB
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