867
FXUS61 KCTP 191907
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
207 PM 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 OF THE LONG
TERM, WITH LINGERING LAKE EFFECT SNOW SHOWERS ACROSS NW PA
FINALLY TAPERING OFF ON SUNDAY. IT WILL BE ANOTHER COLD DAY,
HOWEVER, WITH HIGHS ACROSS CENTRAL PA RUNNING WELL BELOW
AVERAGE (MID TEENS NORTH TO UPPER 20S SOUTH).
THE SFC HIGH IS PROGGED TO DRIFT OF THE EAST COAST SUNDAY NIGHT
INTO MONDAY, WITH A LIGHT SOUTHEASTERLY FLOW DEVELOPING. AFTER
A VERY CHILLY START TO THE DAY, MONDAY AFTERNOON WILL BE A FEW
DEGREES MILDER THAN SUNDAY BUT STILL CHILLY.
CLOUDS WILL BE ON THE INCREASE MONDAY NIGHT, WITH OUR NEXT
WEATHER MAKER BRINGING LIGHT SNOW OR A RAIN/SNOW MIX INTO THE
REGION LATE MONDAY NIGHT INTO TUESDAY. THE WEATHER WILL REMAIN
A BIT UNSETTLED THROUGH THE MIDDLE OF NEXT WEEK, ALTHOUGH WE
SHOULD CONTINUE TO SEE A TREND TOWARDS SLIGHTLY MILDER
TEMPERATURES AS THE WEEK PROGRESSES.
AVIATION /19Z THURSDAY THROUGH TUESDAY/
STILL SOME LINGERING FLURRIES OVER THE LAUREL HIGHLANDS AT MID
MORNING, BUT THESE SHOULD DWINDLE INTO EARLY AFTERNOON AS
INVERSION HEIGHTS SLOWLY LOWER. CEILINGS ACROSS THE ALLEGHENIES
(BFD/JST) WILL GRADUALLY IMPROVE TO HIGH-END MVFR/LOW-END VFR
CRITERIA BY EARLY AFTERNOON 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
NONE.
SYNOPSIS...DEVOIR/STEINBUGL
NEAR TERM...DEVOIR/STEINBUGL
SHORT TERM...DEVOIR/STEINBUGL
LONG TERM...EVANEGO/NPB
AVIATION...GUSEMAN/DEVOIR/FITZGERALD
CLIMATE...STEINBUGL
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