974
FXUS61 KPHI 202339
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
639 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 635 PM, AN UPPER AIR ANALYSIS SHOWED A TROUGH AXIS NEARLY
OVER OUR AREA WITH STRONG VORTICITY ADVECTION MOVING THROUGH.
THIS IS HELPING TO PROVIDE AMPLE FORCING FOR ASCENT AND
WIDESPREAD PRECIPITATION ACROSS MOST OF THE AREA. IT HAS BEEN
DRIER DOWN IN DELMARVA BUT SOME RADAR RETURNS CONTINUE TO
DEVELOP THERE. MUCH OF THE PRECIPITATION IS IN THE FORM OF SNOW
AS COOLING CONTINUES TO ARRIVED FROM THE WEST, ALTHOUGH SOME
LINGERING RAIN CLOSEST TO THE COAST WHICH SHOULD MIX WITH AND
CHANGE TO SOME SNOW AT TIMES. SNOWFALL AMOUNTS HAVE BEEN AS HIGH
AS 1 TO NEARLY 2 INCHES IN PARTS OF THE LEHIGH VALLEY AREA SO
FAR. THERE IS A WEAK SURFACE TROUGH FROM SOUTHEAST NEW JERSEY
NORTHWESTWARD TO NEAR PHILADELPHIA THEN INTO THE LEHIGH VALLEY.
IT IS ROUGHLY IN THIS ZONE WHERE ADDITIONAL SNOW MAY BECOME
MORE FOCUSED THROUGH THE OVERNIGHT. OVERALL, NO SIGNIFICANT
CHANGES MADE TO THE FORECAST WITH THIS UPDATE.
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.
AS WE GO THROUGH THIS EVENING, THE LOW OVER THE OCEAN WILL
CONTINUE TO DEEPEN WHILE PULLING AWAY BUT THERE WILL STILL BE
MULTIPLE IMPULSES OF UPPER LEVEL ENERGY ROTATING THROUGH THE
SLOWING MOVING UPPER LEVEL TROUGH STILL CENTERED NEAR THE COAST.
THIS WILL KEEP PERIODS OF PRECIPITATION GOING ACROSS THE AREA
THAT MAY TEND TO BECOME A LITTLE MORE FOCUSED NEAR AN INVERTED
TROUGH HANGING BACK FROM THE DEPARTING LOW. THAT SAID, MOST OF
THE MODEL GUIDANCE CONTINUES TO DEPICT THIS FEATURE AS BEING
FAIRLY POORLY DEFINED. THE COMBINATION OF DYNAMIC COOLING, WINDS
BACKING MORE TO N/NW AND THE DIURNAL CYCLE WILL LEAD TO THE
RAIN/SNOW LINE COLLAPSING SOUTH/EAST WITH A CHANGE OVER
OCCURING NEAR THE COAST OVERNIGHT, EXCEPT EARLIER IN THE EVENING
OVER PORTIONS OF MONMOUTH COUNTY. THIS WILL OCCUR AS LOW
TEMPERATURES BY MORNING DROP INTO THE UPPER 20S TO LOW 30S FOR
MOST AREAS.
IN TERMS OF SNOWFALL AMOUNTS, ONCE AGAIN, NOT TOO MUCH HAS CHANGED.
GREATEST SNOWFALL TOTALS AROUND 2-3" (LOCALLY 4") ARE EXPECTED
ACROSS THE POCONO PLATEAU OF CARBON AND MONROE COUNTIES AND EXTREME
NORTHERN NEW JERSEY. FOR MOST PORTIONS OF EASTERN PA INTO
CENTRAL/NORTHERN NJ JUST SOUTH OF HERE GENERALLY EXPECT 1-2 WITH
LOCALLY UP TO 3 INCHES. MEANWHILE THE I-95 CORRIDOR, INCLUDING
PHILLY, SHOULD SEE A LIGHT COATING UP TO AN INCH OR SO WITH A LOT OF
THE ACCUMULATION BEING ON GRASSY SURFACES AS OPPOSED TO ROADS WHICH
COULD REMAIN MAINLY WET.
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 /00Z SATURDAY THROUGH WEDNESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
TONIGHT...VARYING CEILINGS, HOWEVER THESE SHOULD SETTLE TO MVFR
AND IFR FOR AWHILE BEFORE IMPROVING SOME TOWARD MORNING.
PERIODS OF LIGHT SNOW WILL RESULT IN MVFR TO IFR VISIBILITIES.
ANY RAIN OR RAIN/SNOW MIX AT KILG, KMIV TO KACY SHOULD
TRANSITION TO SOME SNOW AT TIMES. NORTH-NORTHEAST TO NORTH-
NORTHWEST WINDS MAINLY 5-10 KNOTS. LOW CONFIDENCE WITH THE
DETAILS ESPECIALLY CEILINGS.
SATURDAY...IMPROVING CONDITIONS TO VFR BY MID MORNING, AS ANY
LINGERING LIGHT SNOW ENDS EARLY. NORTHWEST WINDS INCREASING TO 15-20
KNOTS WITH GUSTS TO 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. NE WINDS SHIFTING TO NW AND
MAY DIMINISH FOR A TIME THIS EVENING BEFORE RAMPING UP BY 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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