548
FXUS61 KPHI 210217
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
917 PM EST FRI DEC 20 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 SATURDAY/
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 1-2 INCHES FARTHER NORTH. OPTED TO HOLD OFF ON EXPANDING
THE WINTER WEATHER ADVISORY AS MOST PLACES SHOULD STAY BELOW
CRITERIA AND WITH MORE ACCUMULATIONS ON GRASSY SURFACES COMPARED
TO ROADWAYS. 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 /SATURDAY NIGHT 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 /02Z 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 MID MORNING, 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 SATURDAY FOR PAZ054-055.
COLD WEATHER ADVISORY FROM 8 PM SATURDAY TO 9 AM EST SUNDAY
FOR PAZ054-055.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 5 AM SATURDAY TO MIDNIGHT EST
SATURDAY NIGHT FOR ANZ430-431.
SMALL CRAFT ADVISORY UNTIL 6 AM EST SUNDAY FOR ANZ450>455.
SYNOPSIS...FITZSIMMONS/MJL
NEAR TERM...FITZSIMMONS/GORSE
SHORT TERM...GUZZO
LONG TERM...COOPER
AVIATION...COOPER/FITZSIMMONS/GORSE/GUZZO
MARINE...COOPER/FITZSIMMONS/GUZZO
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