094
FXUS61 KCTP 191221
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
721 AM EST THU DEC 19 2024
SYNOPSIS
*MOSTLY CLOUDY TODAY WITH SCATTERED SNOW SHOWERS AND FLURRIES
DIMINISHING DOWNWIND OF LAKE ERIE OVER THE ALLEGHENY PLATEAU
*WIDESPREAD LIGHT SNOW ACCUMULATION PROBABLE FRIDAY-FRIDAY NIGHT
BEFORE ANOTHER ARCTIC COLD SNAP ARRIVES THIS WEEKEND
*CHILLY AND DRY START NEXT WEEK FOLLOWED BY A GRADUAL WARMUP AND
MIXED PRECIPITATION POTENTIAL CHRISTMAS EVE AND CHRISTMAS DAY
NEAR TERM /THROUGH TONIGHT/
SEASONABLY COLD NW FLOW IS PRODUCING A COUPLE OF SKINNY SNOW BANDS
STREAMING DOWNWIND OF LAKE ERIE OVER THE ALLEGHENY PLATEAU AND
LAUREL HIGHLANDS EARLY THIS MORNING. FCST SOUNDINGS CONTINUE TO
SHOW VERY SHALLOW AND SATURATED MOISTURE PROFILES WITH NO ICE
INTRODUCTION ALOFT; THEREFORE STILL EXPECT SOME PATCHY FREEZING
DRIZZLE TO OCCUR ALONG WITH THE SNOW SHOWERS PARTICULARLY IN
THE LAURELS WHERE KJST CONTINUES TO REPORT UP AT TIMES. A WINTER
WX ADVY REMAINS IN EFFECT UNTIL 8AM.
INVERSION HEIGHTS WILL CONTINUE TO LOWER THROUGH MIDDAY WITH
INCREASING LARGE SCALE SUBSIDENCE AND VEERING/WEAKENING BL FLOW
ASSOCIATED WITH HIGH PRESSURE MIGRATING EASTWARD FROM THE GREAT
LAKES AND OHIO VALLEY. THIS WILL BRING AN END TO ANY LINGERING
SNOW SHOWERS OR FLURRIES. EXPECT SOME BREAKS IN THE CLOUDS
OVER THE LOWER SUSQ VALLEY TO START THE DAY (IR SAT SHOWING
CLEAR POCKETS AT 09Z) WITH HIGHER CLOUDS PEELED OFF TO THE
EAST. MOSTLY CLOUDY SKIES WILL PREVAIL ELSEWHERE WITH MAX TEMPS
NEAR TO AS MUCH AS 5 DEGREES BELOW MID/LATE DECEMBER CLIMO IN
THE 30-40F RANGE.
CLOUDY TONIGHT WITH LOWS IN THE 25-30F RANGE. HIRES MODELS HINT
AT LIGHT SNOW POSSIBLY BREAKING OUT TOWARD DAYBREAK OVER THE
WESTERN ALLEGHENIES. THIS WOULD BE DRIVEN BY INCREASING LLVL
WAA DOWNSTREAM OF PRIMARY CLIPPER SFC-850MB LOW OVER IN/OH AND
SYNOPTIC SCALE LIFT ASSOCIATED WITH 500MB SHORTWAVE TROUGH
AMPLIFICATION UPSTREAM. SHORT TERM ENSEMBLE DATA SHOWS A 150M
HEIGHT FALL CENTER REACHING THE CENTRAL APPALACHIANS BY 12Z
FRIDAY.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/
AS FORCING CONTINUES TO INCREASE, EXPECT COVERAGE OF LIGHT SNOW
TO GRADUALLY EXPAND OVER CPA FRIDAY MORNING. MODELS ARE IN
AGREEMENT IN SECONDARY LOW DEVELOPMENT OFF THE MID ATLANTIC
COAST BY FRIDAY AFTERNOON AS THE PARENT UPPER TROUGH DIGS AND
TAKES ON A NEGATIVE TILT. FOCUS BY THIS TIME WILL HINGE ON
STRENGTH OF LLVL EASTERLY FLOW AND CONVERGENCE AXIS PROGGED TO
SETUP BENEATH THE LEFT EXIT REGION OF A MID/UPPER LEVEL JET
STREAK. THE POTENTIAL INTERACTION OF THESE FEATURES COULD ALLOW
FOR A SLOWLY PIVOTING NNW-SSE ORIENTED BAND OF DEFORMATION SNOW
TO ORGANIZE OVER THE EASTERN PART OF THE FORECAST AREA FRIDAY
AFTERNOON THROUGH FRIDAY NIGHT. THIS OUTCOME WOULD FAVOR HIGHER
SNOWFALL TOTALS TO PERHAPS ADVISORY LEVELS PARTICULARLY OVER
THE HIGHER TERRAIN IN SCHUYLKILL AND SULLIVAN COUNTIES. BUT FOR
NOW, WE STAYED CLOSE TO NBM/WPC QPF/SNOW OUTPUT AND SLRS WITH
OVERALL AMOUNTS RANGING FROM 1-3" IN THE WESTERN AND NORTHERN
MTNS TO A COATING-1" FOR MOST AREAS ALONG AND TO THE SOUTHEAST
OF THE I99/I80 CORRIDOR FROM THE SOUTH CENTRAL ALLEGHENIES
THROUGH THE MID AND LOWER SUSQUEHANNA VALLEY.
INCREASINGLY COLDER NWLY UPSLOPE FLOW ON THE BACKSIDE OF THE
SYSTEM MAY ALSO ENHANCE SNOW TOTALS OVER THE LAUREL HIGHLANDS
THROUGH FRIDAY NIGHT. WPC PROBS ARE SLIGHTLY BETTER THAN 50/50
FOR >4" OF SNOW IN THE TYPICALLY FAVORED WINDWARD SLOPES, SKI
AREAS, AND SUMMITS ABOVE 2000FT PARTICULARLY IN WESTERN
SOMERSET COUNTY NEAR INTERSECTION OF WESTMORELAND/FAYETTE LINE.
THE PATTERN TURNS BRISK AND MUCH COLDER TO START WEEKEND WITH
LAKE EFFECT SNOW SHOWERS AND FLURRIES INTO SATURDAY NIGHT.
MODELS SHOW A POTENTIAL HURON CONNECTION OVER THE WESTERN MTNS
WITH AN ADDITIONAL INCH OR SO POSSIBLE IN THE HIGHER TERRAIN.
HIGHS ON SATURDAY WILL BE 10 TO 15 DEGREES BELOW THE HISTORICAL
AVERAGE WITH MAX TEMPS IN THE 20-30F RANGE. A BRISK AND GUSTY
NW WIND WILL MAKE IT FEEL LIKE THE SINGLE DIGITS/TEENS TO
AROUND 20F. SATURDAY NIGHT WILL BE QUITE COLD WITH MIN TEMPS IN
THE +SINGLE DIGITS TO UPPER TEENS WITH MINIMUM WIND CHILLS FROM
-5F TO +10F INTO EARLY SUNDAY MORNING.
LONG TERM /SUNDAY THROUGH WEDNESDAY/
NORTHWESTERLY FLOW CONTINUES INTO THE BEGINNING STAGES OF THE
LONG-TERM WITH LINGERING LAKE EFFECT SNOW SHOWERS INTO PORTIONS
OF NW PA THROUGH SUNDAY MORNING. NBM POPS DURING THIS TIME SEEM
UNDERDONE, SO HAVE UPPED POPS COMPARED TO PREVIOUS FORECAST
CYCLES WITH A MULTITUDE OF ENSEMBLE GUIDANCE INDICATING SOME
SNOW SHOWERS ACROSS WARREN/MCKEAN/POTTER COUNTIES. NW'LY FLOW
ACROSS PORTIONS OF THE LAUREL HIGHLANDS WILL SUPPORT SOME
MENTIONS OF SNOW SHOWERS; HOWEVER, MUCH LESS CONFIDENCE ON
COVERAGE THIS FAR SOUTH, SO HAVE CAPPED MENTIONS TO A SCHC
MAINLY AHEAD OF SUNRISE SUNDAY. MODEL GUIDANCE DOES CONTINUE TO
INDICATE TEMPERATURES WELL BELOW SEASONAL AVERAGES WITH THE
COLDEST WIND CHILLS ACROSS NE PA BY DAYBREAK SUNDAY. THIS
FORECAST CYCLE CONTINUES TO OUTLINE -5 TO -10 DEGREE WIND CHILLS
ACROSS PORTIONS OF POTTER/TIOGA/SULLIVAN COUNTIES WITH SOME
SIGNALS FOR WIND CHILLS DIPPING BELOW THE -10 DEGREE MARK AT
HIGHER ELEVATIONS OF POTTER COUNTY. NO PLANS ON ANY HEADLINES AT
THIS TIME DUE TO LOWER CONFIDENCE IN TEMPERATURES REACHING
BELOW THRESHOLDS; HOWEVER, WANT TO STRESS THAT IT WILL BE COLD
ACROSS PORTIONS OF NE PA SUNDAY MORNING.
SURFACE HIGH PRESSURE WILL KEEP CONDITIONS DRY WITH
TEMPERATURES SLOWLY MODERATING INTO MONDAY EVENING. MODEL
GUIDANCE BEGINS TO DIVERGE ON TUESDAY WITH RESPECT TO THE NEXT
WEATHER SYSTEM, WITH ECMWF TRENDING DRY THROUGH THE END OF THE
LONG-TERM PERIOD OUTSIDE OF SOME SNOWFALL CHANCES ACROSS THE
NORTHERN TIER WITH THE GFS OUTLINING A MORE ACTIVE PERIOD WITH
RAIN/SNOW ACROSS THE FORECAST AREA ON WEDNESDAY WITH SOME
POTENTIAL FOR DRIER CONDITIONS INTO THURSDAY/FRIDAY. THIS
FORECAST CYCLE STICKS FAIRLY CLOSE TO NBM GUIDANCE GIVEN THIS
SPREAD; HOWEVER, HAVE TAKEN OUT ANY MENTIONS OF FREEZING RAIN AS
CONFIDENCE REMAINS TOO LOW ON TIMING/TRACK TO MENTION ANYTHING
OUTSIDE OF A RAIN/SNOW MIX.
AVIATION /12Z THURSDAY THROUGH MONDAY/
STILL SOME PERIODS OF LIGHT FREEZING DRIZZLE AND SNOW ACROSS
THE AIRFIELDS WEST OF THE SUSQUEHANNA RIVER, BUT THIS WILL COME
TO AN END BY MID MORNING WITH DRY CONDITIONS PREVAILING THROUGH
THE DAY. MVFR/IFR CEILINGS ACROSS THE ALLEGHENIES (BFD/JST) WILL
GRADUALLY IMPROVE LATER THIS MORNING AND THIS AFTERNOON TO
HIGH-END MVFR/LOW-END VFR CRITERIA AS DRIER/SINKING AIR MOVES
IN.
CLOUDS WILL BEGIN TO INCREASE AND LOWER AGAIN THIS EVENING AND
OVERNIGHT AS A CLIPPER SYSTEM APPROACHES TONIGHT INTO FRIDAY,
BRINGING LIGHT SNOW TO THE CENTRAL PA AIRSPACE FRIDAY. BFD/JST
WILL STAND THE BEST CHANCE OF DEGRADING CEILINGS BETWEEN 06-12Z
FRIDAY.
OUTLOOK...
FRI...LIGHT SNOW/LOW CIGS LIKELY, MAINLY N AND W MTNS.
SAT...NW WINDS GUSTING TO AROUND 25KTS. AM SNOW SHOWERS
POSSIBLE N AND W MTNS.
SUN-MON...NO SIG WX EXPECTED.
CLIMATE
ASTRONOMICAL WINTER (SOLSTICE) BEGINS ON SATURDAY, DECEMBER 21ST
AT 4:19 A.M. EST.
CTP WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 8 AM EST THIS MORNING FOR PAZ024-
033.
SYNOPSIS...STEINBUGL
NEAR TERM...STEINBUGL
SHORT TERM...STEINBUGL
LONG TERM...NPB
AVIATION...GUSEMAN/FITZGERALD
CLIMATE...STEINBUGL
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