907
FXUS61 KPHI 210549
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1249 AM EST SAT DEC 21 2024
SYNOPSIS
LOW PRESSURE IMPACTS THE REGION INTO EARLY SATURDAY. A STRONG
AND COLD HIGH PRESSURE SYSTEM BEGINS TO BUILD IN LATER SATURDAY,
HOLDING INFLUENCE OVER THE REGION THROUGH MONDAY AND BRINGING
FRIGID TEMPERATURES WITH IT. NEXT LOW PRESSURE SYSTEM COULD
IMPACT THE REGION MONDAY NIGHT INTO CHRISTMAS EVE.
NEAR TERM /THROUGH TODAY/
1 AM UPDATE: THE HEAVIER ACCUMULATING SNOWFALL IS BEGINNING TO
WANE IN INTENSITY. THIS IS EVIDENT IN LESSENING RADAR
REFLECTIVITY AND IMPROVING ASOS VISIBILITIES. HOWEVER, PERIODS
OF LIGHT SNOW AND SOME ADDITIONAL ACCUMULATIONS OF A FEW TENTHS
OF AN INCH ARE POSSIBLE WITHIN THE ADVISORY AND ADJACENT AREAS,
SO WE'LL LEAVE THE ADVISORY IN EFFECT FOR NOW. SO FAR,
WIDESPREAD AMOUNTS OF 1-4" HAVE BEEN REPORTED GENERALLY NEAR THE
PHILLY METRO AND NORTH.
AS OF 1015 PM, GIVEN ADDITIONAL MODEL GUIDANCE AND SNOWFALL
REPORTS SO FAR OPTED TO EXPAND THE WINTER WEATHER ADVISORY TO
INCLUDE THE LEHIGH VALLEY, BUCKS COUNTY, MERCER TO SOMERSET
COUNTIES NORTHWARD. STORM TOTALS OF 2-4 INCHES OVERALL IN THESE
AREAS. FARTHER SOUTH AND WEST, THE SNOW IS GRADUALLY LESSENING
WITH THE MORE FOCUSING TENDING TO SHIFT FARTHER NORTH WHERE
GUIDANCE DEVELOPS MORE SNOW OVERNIGHT INTO EARLY SATURDAY
MORNING.
AS OF 915 PM, AN UPPER AIR ANALYSIS SHOWED AN UPPER-LEVEL
TROUGH AXIS OVER OUR AREA WITH STRONG VORTICITY ADVECTION
CONTINUING TO MOVE THROUGH. THIS IS PROVIDING AMPLE FORCING FOR
ASCENT AND WIDESPREAD PRECIPITATION ACROSS MOST OF THE AREA.
THERE HAS BEEN MUCH LESS PRECIPITATION ACROSS OUR DELMARVA
ZONES, HOWEVER SOME LIGHT RAIN AND SNOW HAS BEEN REPORTED IN
SOME AREAS. A SURFACE ANALYSIS SHOWS A WEAK TROUGH WHICH HAS
SHIFTED A BIT NORTHWARD FROM EARLIER AND RUNS FROM ABOUT JUST
NORTH OF ATLANTIC CITY TO BETWEEN TRENTON AND PHILADELPHIA AND
INTO THE POCONOS. THE RADAR TRENDS ALSO SHOW THE ENHANCED AREA
OF SNOW, MORE LARGER SNOWFLAKES RESULTING IN MORE EFFICIENT
ACCUMULATIONS, ALSO GRADUALLY SHIFTING EAST AND NORTH. SOME
HIGHER SNOW TOTALS ON THE ORDER OF 2-3 INCHES HAVE BEEN REPORTED
SO FAR IN PARTS OF THE LEHIGH VALLEY, POCONOS INTO UPPER
BUCKS/MONTGOMERY COUNTIES. GUIDANCE, ESPECIALLY THE HRRR,
FOCUSES ADDITIONAL SNOW ACROSS OUR NORTHERN TO CENTRAL AREAS
OVERNIGHT AS THE SURFACE TROUGH LIFTS A BIT MORE NORTHWARD.
THERE ARE SOME MODELS HOWEVER THAT SNOW ADDITIONAL SNOW FARTHER
SOUTH SOME FOR A TIME OVERNIGHT INTO EARLY SATURDAY MORNING.
UPDATED THE SNOW AMOUNTS TO REFLECT SOME HIGHER ADDITIONAL
ACCUMULATIONS WITH AROUND AN INCH IN THE IMMEDIATE PHILLY METRO
INCLUDING THE ADJACENT NEW JERSEY ZONES WITH 1-3 INCHES FARTHER
NORTH. THERE WILL BE SLIPPERY CONDITIONS THOUGH DUE TO WET
PAVEMENT AND WHERE SOME LIGHT SNOW ACCUMULATIONS OCCUR ON ROADS,
PARKING LOTS AND WALKWAYS.
OTHERWISE, A COMPLEX SYSTEM CONTINUES TO EVOLVE AS IT'S
AFFECTING THE AREA WITH SOME RAIN AND SNOW. AT THE SURFACE, A
PRIMARY LOW HAS WEAKENED OVER OHIO WHILE A SECONDARY LOW
DEVELOPING A COUPLE HUNDRED MILES EAST OF DELMARVA IS
STRENGTHENING AND MOVING NORTH AND EAST. THIS IS OCCURING AS A
DEEPENING UPPER LEVEL TROUGH IS PIVOTING TOWARDS THE COAST
PLACING THE AREA IN A FAVORABLE SPOT FOR LIFT AS DISTURBANCES
CONTINUE TO ROTATE AROUND THE BASE OF THE TROUGH. IT'S IN THE
20S ACROSS THE POCONO PLATEAU WHERE WE MAINTAIN A WINTER WEATHER
ADVISORY FOR CARBON AND MONROE COUNTIES.
LOW TEMPERATURES INTO THE UPPER 20S TO LOW 30S FOR MOST AREAS,
THEREFORE WATCH FOR SOME ICY SPOTS ON WET UNTREATED SURFACES
ESPECIALLY BRIDGES AND OVERPASSES.
PRECIPITATION WILL COME TO AN END WEST TO EAST LATE TONIGHT
INTO SATURDAY MORNING AS THE LOW CONTINUES TO PULL AWAY TO THE
NORTH AND EAST WHILE CONTINUING TO RAPIDLY DEEPEN. BEHIND THE
DEPARTING LOW, A VERY TIGHT PRESSURE GRADIENT WILL FORM AS
STRONG CANADIAN HIGH PRESSURE WILL BUILD IN FROM THE NORTH AND
WEST, LEADING TO WINDY CONDITIONS DURING THE DAY SATURDAY WITH
NW WINDS 15-20 MPH AND GUSTS UP TO 30 MPH. COMBINED WITH
AFTERNOON TEMPERATURES IN THE UPPER 20S TO MID 30S, WE WILL BE
LOOKING AT WIND CHILLS IN THE TEENS AND 20S FOR MUCH OF THE DAY.
WIND CHILLS IN THE POCONOS LOOK TO LINGER IN THE SINGLE DIGITS
ALL DAY.
SHORT TERM /TONIGHT THROUGH MONDAY/
AS OUR LOW PRESSURE SYSTEM EXITS, WE SEE A PRESSURE GRADIENT
TIGHTEN WITH CANADIAN HIGH PRESSURE BUILDING INTO THE REGION
FROM THE NORTH AND WEST. THIS WILL LEAD TO WINDY CONDITIONS WITH
A NW WIND OF 10-15 MPH AND GUSTS UPWARDS OF 30 MPH. THE REAL
STORY AT THIS POINT BECOMES THE COLD CONDITIONS WE WILL
EXPERIENCE. SINGLE DIGITS FOR THE POCONOS AND WIDESPREAD TEENS
ELSEWHERE AS THIS ARCTIC AIR FILTERS IN. WHEN YOU FACTOR IN THE
WIND THAT WAS MENTIONED ABOVE, WIND CHILLS WILL BE IN THE SINGLE
DIGITS FOR MOST, EVEN FEELING SEVERAL DEGREES BELOW ZERO FOR
THE POCONO PLATEAU! ZOOMING IN ON THE POCONOS AND GIVEN THE
FORECAST, A COLD WEATHER ADVISORY HAS BEEN ISSUED FOR CARBON AND
MONROE COUNTY. THE CRITERIA FOR THE ADVISORY IS -10 WHICH IS
EXPECTED TO BE MET WITH WIND CHILLS REACHING AS LOW AS -10 TO
-12 SATURDAY NIGHT.
DAYTIME HIGHS ON SUNDAY WILL BE VERY COLD! HIGHS WILL BE IN THE
TEENS FOR THE POCONOS AND PLENTY OF 20S ELSEWHERE. ONE POSITIVE
IS THAT THE WIND DECREASES THROUGHOUT THE DAY SUNDAY AS HIGH
PRESSURE MOVES OVERHEAD. WIND CHILLS WILL BE IN THE TEENS
(POCONOS WILL SEE WIND CHILLS DOWN TO THE SINGLE DIGITS). COME
SUNDAY NIGHT INTO EARLY MONDAY MORNING, WINDS WILL BECOME MOSTLY
CALM, BUT STRONG RADIATIONAL COOLING IS EXPECTED WITH A CLEAR
SKY. AS A RESULT, WE WILL RADIATE VERY EFFICIENTLY AND
TEMPERATURES ARE EXPECTED TO CRATER INTO THE SINGLE DIGITS FOR
MUCH OF THE REGION WITH THE PHILLY METRO, COASTAL AREAS, AND THE
DELMARVA IN THE LOW-TEENS. GIVEN THE CALMER WINDS, HOWEVER,
WIND CHILLS WILL NOT BE TOO DIFFERENT, BUT STILL BE IN THE
SINGLE DIGITS FOR MOST OF THE REGION.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
BEGINNING ON MONDAY EVENING,ENHANCED MID AND UPPER-LEVEL FLOW
FROM AN APPROACHING TROUGH WILL BEGIN TO OVERSPREAD THE REGION.
IN RESPONSE, A WEAK SURFACE LOW WILL TRAVERSE THE NORTHERN PARTS
OF OUR REGION, LEADING TO INCREASED CHANCES FOR PRECIPITATION
ACROSS THE AREA, PARTICULARLY FROM LATE MONDAY NIGHT AND INTO
THE DAY ON TUESDAY. RIGHT NOW, PRECIPITATION AMOUNTS APPEAR
LIGHT, AND TEMPERATURES LOOK TO WARM INTO THE MID/UPPER 30S
ACROSS MUCH OF THE AREA DURING THE DAY ON TUESDAY. WITH THAT
SAID, IT IS POSSIBLE THAT A LITTLE WINTRY PRECIPITATION COULD
OCCUR WITH THE PASSAGE OF THIS SYSTEM. AS OF RIGHT NOW, IT
APPEARS THAT THIS WOULD BE MOST LIKELY ACROSS CENTRAL AND
NORTHERN PORTIONS OF THE FORECAST AREA.
THERE IS SOME INDICATION THAT AN ADDITIONAL WEAK IMPULSE COULD
BRING A SLIGHT CHANCE FOR LIGHT RAIN AND SNOW ACROSS PORTIONS OF
THE AREA PRIMARILY ON THURSDAY. OTHERWISE, IT APPEARS THAT MID-
LEVEL RIDGING WILL BEGIN TO SET IN TOWARDS THE END OF THE WEEK
WITH DRY CONDITIONS AND TEMPERATURES NEAR SEASONAL NORMALS.
AVIATION /06Z SATURDAY THROUGH WEDNESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
TONIGHT...MVFR TO IFR CEILINGS, WHICH SHOULD IMPROVE SOME
TOWARD MORNING. PERIODS OF LIGHT SNOW WILL RESULT IN MVFR TO IFR
VISIBILITIES. NORTH-NORTHWEST WINDS 5-10 KNOTS, WHICH MAY
DECREASE SOME FOR A TIME OVERNIGHT. LOW CONFIDENCE WITH THE
DETAILS ESPECIALLY CEILINGS/VISIBILITIES.
SATURDAY...ANY MVFR IMPROVES TO VFR BY 15Z, AS ANY LINGERING
LIGHT SNOW ENDS EARLY. NORTHWEST WINDS INCREASING TO 15-20 KNOTS
WITH GUSTS 25-30 KNOTS. MODERATE CONFIDENCE.
OUTLOOK...
SATURDAY NIGHT THROUGH MONDAY...VFR CONDITIONS ARE EXPECTED
THROUGH AT LEAST MONDAY NIGHT. NO SIGNIFICANT WEATHER IS
EXPECTED.
TUESDAY...MVFR CONDITIONS POSSIBLE WITH A SYSTEM MOVING IN FROM
THE GREAT LAKES.
WEDNESDAY...CONDITIONS SHOULD IMPROVE TO VFR.
MARINE
SCA REMAINS IN EFFECT THROUGH SATURDAY. N WINDS SHIFTING TO NW
AND RAMPING UP LATER TONIGHT THROUGH SATURDAY WITH GUSTS UP TO
30 KNOTS SATURDAY. SEAS GENERALLY 4-7 FEET.
OUTLOOK...
SUNDAY THROUGH WEDNESDAY...SCA CONDITIONS MAY LINGER INTO EARLY
SUNDAY MORNING. OTHERWISE, MARINE CONDITIONS WILL REMAIN BELOW
ADVISORY CRITERIA THROUGH WEDNESDAY.
PHI WATCHES/WARNINGS/ADVISORIES
PA...WINTER WEATHER ADVISORY UNTIL 7 AM EST THIS MORNING FOR PAZ054-
055-061-062-105-106.
COLD WEATHER ADVISORY FROM 8 PM THIS EVENING TO 9 AM EST
SUNDAY FOR PAZ054-055.
NJ...WINTER WEATHER ADVISORY UNTIL 7 AM EST THIS MORNING FOR NJZ001-
007>010-015.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 5 AM EARLY THIS MORNING TO MIDNIGHT
EST TONIGHT FOR ANZ430-431.
SMALL CRAFT ADVISORY UNTIL 6 AM EST SUNDAY FOR ANZ450>455.
SYNOPSIS...FITZSIMMONS/MJL
NEAR TERM...FITZSIMMONS/GORSE/STAARMANN
SHORT TERM...GUZZO
LONG TERM...COOPER
AVIATION...COOPER/FITZSIMMONS/GORSE/GUZZO/STAARMANN
MARINE...COOPER/FITZSIMMONS/GUZZO
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