553
FXUS61 KCTP 181504
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1004 AM EST WED DEC 18 2024
SYNOPSIS
* PRECIPITATION ARRIVES THIS AFTERNOON WITH RAIN LIKELY SOUTH
OF I-80 AND SNOW OR A WINTRY MIX ACROSS THE NORTHERN MOUNTAINS
* A CLIPPER WILL BRING LIGHT SNOW TO MOST OF THE AREA ON FRIDAY
* CONSIDERABLY COLDER FOR THE WEEKEND.
NEAR TERM /UNTIL 6 PM THIS EVENING/
MID TO HIGH CLOUDS STREAMING EASTWARD WITH THE MIDDLE TO LOWER
SUSQ LIKELY TO CLOUD OVER BY MIDDAY AS WEAK SFC HIGH RETREATS.
THE DECK OF HIGH CLOUDS WILL CONTINUE TO SHIFT EASTWARD ACROSS
PENNSYLVANIA THIS MORNING AHEAD OF A A WEAK AND FAST-MOVING
SURFACE LOW MOVING THROUGH THE OHIO VALLEY. MOST LOCATIONS
SHOULD STAY DRY THROUGH LUNCHTIME WITH HIGH TEMPERATURES (PRIOR
TO PRECIPITATION ONSET) RANGING FROM THE MID 30S IN THE
NORTHWEST MOUNTAINS TO NEAR 50 IN EXTREME SOUTHEAST PA.
PRECIPITATION IS OVERSPREADING THE ALLEGHENIES LATE THIS MORNING
AND WILL MOVE ACROSS THE AREA RAPIDLY THIS AFTERNOON.
ISOTHERMAL SOUNDINGS STRADDLING THE ZERO LINE THROUGH THE
BOUNDARY LAYER LIE ACROSS THE I-80 CORRIDOR. WHILE A FEW WET
FLAKES MAY MIX IN IMMEDIATELY SOUTH OF I-80, PREDOMINANT PTYPE
IS RAIN FOR STATE COLLEGE JOHNSTOWN AND ALTOONA GIVEN LACK OF
VIGOROUS UVV ACROSS CENTRAL AND NORTHERN PA, WITH BEST LIFT AT
THE NOSE OF 850 MB JET NOSING INTO SOUTH CENTRAL AND SOUTHEAST
PA. NORTH OF I-80, SLUSHY COATINGS TO LOCALLY 1-2"+ ARE EXPECTED
WITH HIGHEST AMOUNTS OVER THE NW MOUNTAINS. WAA AND CONVERGENCE
ALONG THE AFOREMENTIONED LLJ SUPPORT CATEGORICAL POPS THIS
AFTERNOON AND EVENING.
SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/
EXPECT PRECIPITATION TO TAPER OFF FROM WEST TO EAST THIS
EVENING, AS THE WAVE OF LOW PRESSURE SLIDES EAST OF PA. ENSEMBLE
MEAN QPF BY THIS EVENING RANGES FROM 0.15 TO 0.40 INCHES, WITH
THE HEAVIEST AMOUNTS OVER SOMERSET AND SCHUYLKILL COUNTIES,
WHERE OROGRAPHIC ENHANCEMENT IS MAXIMIZED. FORECAST SOUNDINGS
INDICATE SNOW WILL BE CONFINED TO THE N MTNS WEDNESDAY, WHERE
1-2 INCHES ARE POSSIBLE OVER THE HIGHER TERRAIN.
RESIDUAL LOW LEVEL MOISTURE ASCENDING THE ALLEGHENIES SHOULD
RESULT IN LINGERING LIGHT RAIN/SNOW OVER THE WESTERN COUNTIES
EARLY THIS EVENING, WHILE A DOWNSLOPING NORTHWEST FLOW RESULTS
IN DEVELOPING BREAKS IN THE OVERCAST FURTHER EAST. THE AIRMASS
CROSSING THE GRT LKS THEN BECOMES COLD ENOUGH TO SUPPORT
SCATTERED, OROGRAPHICALLY-ENHANCED, LAKE EFFECT SNOW SHOWERS
OVER THE W MTNS LATE WED NIGHT. LOW INVERSION HEIGHTS INDICATE
ANY ACCUMULATIONS WILL BE VERY LIGHT (<0.5 INCHES). MODEL
SOUNDINGS ACTUALLY INDICATE SHALLOW CLOUD DEPTHS MAY RESULT IN
PATCHY -FZDZ, RATHER THAN -SHSN, OVER THE RIDGETOPS OF THE
LAUREL HIGHLANDS.
THE WINDOW FOR LAKE EFFECT SNOW SHOWERS OVER NW PA EXTENDS INTO
MIDDAY THURSDAY WITH GENERALLY LIGHT ACCUMS EXPECTED. TYPICAL
NORTHWEST FLOW PATTERN ON THURSDAY WITH BREAKS IN THE CLOUDS IN
SE PA DURING THE AFTERNOON AND PERSISTENT STRATOCUMULUS FARTHER
NORTHWEST. HIGHS ON THURSDAY WILL TREND CLOSE TO NORMAL WITH
HIGHS IN THE LOW 30S TO LOW 40S. AN APPROACHING CLIPPER SYSTEM
WILL TURN WINDS EASTERLY THURSDAY NIGHT, SUPPORTING A DRY BUT
DREARY NIGHT WITH PLENTY OF LOW CLOUDS AND PERHAPS SOME REDUCED
VISIBILITY. LOWS IN THE MID 20S WILL COOL THE GROUND ENOUGH TO
ALLOW ANY SNOW THAT FALLS ON FRIDAY TO STICK TO
UNTREATED/ELEVATED SURFACES.
LONG TERM /FRIDAY THROUGH TUESDAY/
10PM UPDATE...AFTER THE FRIDAY CLIPPER IT WILL BE VERY COLD,
WITH MAXES ONLY IN THE 20S-L30S SATURDAY AND MIDTEENS-MID20S
SUNDAY. OVERNIGHT LOWS LIKELY CHALLENGE 0F IN THE N (SUN AM).
ALMOST EVERYONE WILL DROP INTO THE SINGLE DIGITS MON AM. WIND
CHILLS DO GET NEAR -10F SUN AM IN THE NE, BUT NOT ON MON AM
WHEN THE WIND IS LIGHTER/CALM UNDER THE SFC HIGH DESPITE THE
COLDER AIR TEMPS.
PREV...
A MOISTURE CHALLENGED CLIPPER SYSTEM WILL BRING A PERIOD OF
LIGHT SNOW OR SNOW SHOWERS OVER WESTERN AND CENTRAL PARTS OF PA
ON FRIDAY. THIS FEATURE LOSES ITS SURFACE REFLECTION LATE FRIDAY
AS ITS PARENT UPPER TROUGH PHASES OFF THE MID ATLANTIC SHORE TO
STRENGTHEN AN OCEAN STORM THAT RACES SOUTHEAST OF NEW ENGLAND
FRI NIGHT AND SATURDAY. RESIDUAL DEFORMATION ZONE FLURRIES OR
SNOW SHOWERS APPEAR LIKELY FRIDAY NIGHT INTO EARLY SATURDAY OVER
MAINLY THE ALLEGHENIES AND N CENTRAL MOUNTAINS, FOLLOWED BY
SOME LAKE EFFECT SNOW SHOWERS INTO THE NW MOUNTAINS FOR THE
REMAINDER OF SATURDAY AND INTO SUNDAY. ACCUMS WITH THE CLIPPER
FRIDAY APPEAR LIGHT, GENERALLY A COATING ACROSS CENTRAL AREAS
AND A COATING TO PERHAPS A FEW INCHES OVER THE HIGHER WESTERN
AND NORTHERN TERRAIN, WITH ADDITIONAL LIGHT LAKE EFFECT ACCUMS
CONFINED TO THE NW MOUNTAINS. EVEN COLDER CONDITIONS ARRIVE FOR
SUNDAY AS THE ARCTIC HIGH BUILDS OVER NW PA SUNDAY NIGHT
PRODUCING WIDESPREAD MINS IN THE SINGLE DIGITS ABOVE ZERO MONDAY
MORNING.
AVIATION /15Z WEDNESDAY THROUGH SUNDAY/
LIFR STRATUS AND DENSE FOG IMPACTING KBFD AND KIPT EARLY THIS
MORNING SHOULD PERSIST THROUGH SUNRISE WITH IMPROVEMENT MOST
LIKELY AT KIPT. ELSEWHERE, PREVAILING VFR WILL GRADUALLY TREND
LOWER THROUGH THE AFTERNOON TO MVFR AND IFR AS PRECIP SPREADS
FROM SOUTHWEST TO NORTHEAST ACROSS THE AIRSPACE. TEMPS WILL BE
COLD ENOUGH FOR SNOW AT KBFD. AS PRECIP EXITS THE EASTERN
TERMINALS 04-06Z, A WINDSHIFT TO 280-320 DEGREES WILL FAVOR
CONTINUED IFR/LIFR AT KBFD/KJST WHILE SITES TO THE EAST OF THE
MTNS BEGIN TO IMPROVE TO MVFR OR LOW END VFR. SNOW SHOWERS AND
PATCHY FREEZING DRIZZLE WILL LIKELY IMPACT KBFD AND KJST
OVERNIGHT INTO EARLY THURSDAY MORNING.
OUTLOOK...
THU...SNOW SHOWERS AND FLURRIES ENDING BY THURSDAY NIGHT.
MVFR/IFR WEST TO LOW VFR EAST.
FRI...IFR LIKELY IN LIGHT SNOW.
SAT-SUN...IFR/MVFR IN SNOW SHOWERS AT BFD/JST. MVFR TO LOW END
VFR ELSEWHERE WITH FLURRIES.
CLIMATE
ASTRONOMICAL WINTER (SOLSTICE) BEGINS ON SATURDAY, DECEMBER 21ST
AT 4:19 A.M. EST.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...DEVOIR/BANGHOFF
NEAR TERM...DEVOIR/FITZGERALD/BANGHOFF
SHORT TERM...FITZGERALD/BANGHOFF
LONG TERM...LAMBERT/DEVOIR/DANGELO/BAUCO
AVIATION...STEINBUGL
CLIMATE...STEINBUGL
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