307
FXUS61 KPHI 301738
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1238 PM EST MON DEC 30 2024
SYNOPSIS
A COLD FRONT SHIFTS OFFSHORE EARLY THIS MORNING AS STRONG LOW
PRESSURE MOVES ACROSS THE GREAT LAKES AND INTO SOUTHERN CANADA.
A WEAK AREA OF HIGH PRESSURE THEN BUILDS ACROSS OUR AREA TONIGHT
BEFORE MOVING OFFSHORE TUESDAY. LOW PRESSURE MOVES ACROSS THE
AREA TUESDAY NIGHT INTO EARLY WEDNESDAY FOLLOWED BY A COLD FRONT
ON WEDNESDAY. BEYOND THIS TIME, IT TURNS MUCH COLDER AS A STRONG
NORTHWEST FLOW OCCURS THROUGH THE END OF THE WEEK AND INTO THE
WEEKEND.
NEAR TERM /THROUGH TONIGHT/
ONLY SOME MINOR ADJUSTMENTS WILL BE MADE TO THE DATABASE AS THE
FORECAST IS ON TRACK.
A TIGHTENING PRESSURE GRADIENT ALONG WITH SOME COLD AIR
ADVECTION THOUGH THROUGH THE DAY WILL RESULT IN DEEPER MIXING
OCCURRING AS THE BOUNDARY LAYER REMAINS ON THE MILD SIDE. THIS
WILL RESULT IN A NOTABLE INCREASE IN A WEST-SOUTHWEST BREEZE
WITH GUSTS UP TO ABOUT 30 MPH. SOME STRATOCUMULUS OR CUMULUS
MAY DEVELOP OR HANG ON FROM ABOUT THE I-95 CORRIDOR ON NORTH AND
WEST. THE MOST CLOUD COVER MAY LAST THE LONGEST IN THE VICINITY
OF THE POCONOS. WHILE IT WILL BE A MILD DAY, JUST ENOUGH COLD
AIR ADVECTION SHOULD KEEP THE HIGH TEMPERATURES SEVERAL DEGREES
LOWER THAN WHAT WAS OBSERVED YESTERDAY. THERE WILL ALSO BE A
DECENT AMOUNT OF DRY AIR ADVECTION OCCURRING TODAY AND THEREFORE
THE SURFACE DEW POINTS WILL LOWER INTO AND THROUGH THE 40S AND
EVENTUALLY INTO THE 30S BY THE END OF THE DAY.
THE UPPER-LEVEL TROUGH LIFTS NORTHWARD AND FARTHER AWAY FROM
OUR AREA TONIGHT AND THE PRESSURE GRADIENT THEREFORE RELAXES
ESPECIALLY AS SOME WEAK MIDLEVEL RIDGING ARRIVES. THE SKY SHOULD
BE MOSTLY CLEAR FOR NEARLY THE ENTIRE AREA, HOWEVER THE NEXT
SYSTEM IN THE FORM OF SHORTWAVE TROUGH WILL BE MOVING INTO THE
OHIO VALLEY OVERNIGHT. THIS SHOULD START TO SEND SOME HIGH LEVEL
CLOUDS OUR WAY OVERNIGHT. IT WILL TURN COLDER TONIGHT AS THE
WINDS DIMINISH IN THE EVENING, WITH LOW TEMPERATURES FALLING
INTO THE UPPER 20S TO LOW TO MID 30S ACROSS THE REGION.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
WEAK RIDGING WITH MAINLY CLEAR SKIES WILL BE PRESENT OVER THE AREA
TO START THE DAY TUESDAY. HOWEVER THIS WILL GIVE WAY TO INCREASING
CLOUDS THROUGH THE DAY AS THE NEXT AREA OF LOW PRESSURE APPROACHES.
EXPECT THAT BY LATE IN THE DAY A PRIMARY LOW WILL BE MOVING NORTH
AND EAST INTO OHIO / WESTERN PA WITH A SECONDARY LOW STARTING TO
TAKE SHAPE ACROSS DELMARVA NEAR THE SYSTEM'S TRIPLE POINT WHERE
THERE WILL BE STRONG PVA SETTING UP AS A FAIRLY POTENT UPPER TROUGH
SWINGS THROUGH. THIS SHOULD START TO SPREAD SOME RAIN INTO DELMARVA
AS WELL AS PARTS OF SE PA AND SOUTHERN NJ BY LATE AFTERNOON. IT WILL
BE ANOTHER MILD DAY FOR THIS TIME OF YEAR WITH HIGHS MOSTLY IN THE
50S EXCEPT 40S OVER THE SOUTHERN POCONOS AND NW NJ.
FOR TUESDAY NIGHT, SECONDARY COASTAL LOW DEEPENS AND MOVES RIGHT
OVER THE AREA AS VORT MAX ALOFT SWINGS THROUGH. THIS WILL BRING
THE AREA A PERIOD OF RAIN, POTENTIALLY HEAVY AT TIMES, TUESDAY
EVENING INTO THE EARLY PART OF THE OVERNIGHT BEFORE PRECIP
STARTS TO TAPER OFF FROM SW TO NE LATE. GENERALLY EXPECT
RAINFALL AMOUNTS OF ONE THIRD TO TWO THIRDS OF AN INCH WITH
LOCALLY UP TO AN INCH POSSIBLE IN PLACES. SO NOT ENOUGH TO CAUSE
ANY HYDRO CONCERNS AND WE ALSO DON'T EXPECT ANY WINTRY PRECIP
CONCERNS THROUGH TUESDAY NIGHT AS LOWS WILL BE MAINLY IN THE
UPPER 30S AND 40S.
BY WEDNESDAY, A STILL DEEPENING COASTAL LOW WILL BE MOVING AWAY FROM
THE AREA IS IT MOVES N/E ALONG THE COAST OF NEW ENGLAND WHILE AN
ELONGATED ARCTIC HIGH WILL BE BUILDING IN TO OUR WEST AS IT EXTENDS
FROM THE CANADIAN ROCKIES INTO THE CENTRAL US. THIS WILL HELP USHER
A COLD FRONT THROUGH THE AREA WITH A VERY STRONG PRESSURE GRADIENT
ALSO SETTING UP. EXPECT WESTERLY WINDS INCREASING TO 15 TO 25
GUSTING 30 TO 40 MPH OR SO MEANING NOT TOO FAR OFF FROM WIND
ADVISORY LEVELS. THERE MAY ALSO BE SOME LINGERING RAIN/SNOW SHOWERS
AROUND ON THE BACKSIDE OF THE SYSTEM, ESPECIALLY OVER THE SOUTHERN
POCONOS AND NW NJ AS THESE AREAS COULD SEE THE TAIL END OF SOME LAKE
EFFECT INFLUENCES. WITH THE COLD ADVECTION PATTERN IN PLACE, ANY
RAIN OR MIXED PRECIP SHOWERS WILL CHANGE OVER TO SNOW SHOWERS BY
LATE DAY. OTHERWISE EXPECT PARTLY TO MOSTLY CLOUDY SKIES TO
ACCOMPANY THE STRONG WINDS WITH HIGHS MAINLY IN THE UPPER 40S TO LOW
50S EXCEPT AROUND 40 OVER THE POCONO PLATEAU.
THE COLD ADVECTION PATTERN WITH BLUSTERY CONDITIONS CONTINUES
WEDNESDAY NIGHT AS THE STRONG PRESSURE GRADIENT REMAINS IN PLACE.
THIS WILL RESULT IN LOWS BY THURSDAY MORNING GETTING DOWN INTO THE
20S TO LOW 30S UNDER MAINLY CLEAR TO PARTLY CLOUDY SKIES. HOWEVER
THE CONTINUING WINDY CONDITIONS WILL MAKE IT FEEL EVEN COLDER WITH
THE WIND CHILL FACTORED IN.
LONG TERM /THURSDAY THROUGH SUNDAY/
ONCE THE MID-WEEK STORM SYSTEM DEPARTS THE AREA, MID-LEVEL TROUGHING
CAN BE EXPECTED TO SETTLE INTO MUCH OF THE EASTERN US LATE THIS WEEK
AND INTO THE WEEKEND. ACROSS THE AREA, 500 MB NORTHWESTERLY FLOW ON
THE ORDER OF 35-45 KT WILL CONTINUE INTO SATURDAY, WITH SURFACE COLD
ADVECTION CONTINUING. THE RESULT WILL BE BELOW NORMAL TEMPERATURES
ACROSS THE AREA. THE WARMEST DAY OF THE EXTENDED PERIOD LOOKS TO BE
THURSDAY, WITH HIGH TEMPERATURES RANGING FROM THE LOW 40S ACROSS
PORTIONS OF THE DELMARVA AND SOUTHERN NEW JERSEY TO THE UPPER 20S
AND LOWER 30S ACROSS THE POCONOS. BEYOND THAT, HIGH TEMPERATURES
THROUGH THE WEEKEND LOOK TO RANGE FROM THE MID-UPPER 20S TO THE MID
30S AREAWIDE, WITH LOW TEMPERATURES IN THE TEENS AND 20S.
THERE ARE SOME INDICATIONS IN MODEL GUIDANCE THAT A FEW WEAK MID-
LEVEL PERTURBATIONS IN COMBINATION WITH CONTINUING NORTHWESTERLY
FLOW COULD LEAD TO SOME LIGHT PRECIPITATION CHANCES ACROSS THE AREA
FRIDAY INTO SATURDAY. CHANCES FOR MEANINGFUL PRECIPITATION APPEAR TO
BE SMALL AT THIS TIME HOWEVER, WITH MOST LOCATIONS SIMPLY BEING DRY
AND COLD.
BY THE VERY END OF THE WEEKEND INTO EARLY NEXT WEEK, ATTENTION WILL
SHIFT TO A LOW PRESSURE SYSTEM APPROACHING FROM THE WEST.
SIGNIFICANT MODEL DISCREPANCIES EXIST REGARDING THE HANDLING OF THIS
POTENTIAL SYSTEM, AND IT IS TOO SOON TO SPECULATE ON EXACT IMPACTS
TO THE AREA. WITH THAT BEING SAID, WINTRY PRECIPITATION CHANCES WILL
BE ON THE INCREASE ACROSS PORTIONS OF THE AREA BEGINNING LATE THIS
WEEKEND.
AVIATION /18Z MONDAY THROUGH SATURDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
TODAY...VFR. WEST-SOUTHWEST 10-15 KNOTS WITH GUSTS UP TO 25
KNOTS BY MIDDAY. THE WINDS WILL THEN START TO DIMINISH TOWARD
LATE AFTERNOON. MODERATE CONFIDENCE.
TONIGHT...VFR. WEST-SOUTHWEST WINDS DIMINISHING TO 5-8 KNOTS EARLY
IN THE EVENING, THEN BECOMING LIGHT AND VARIABLE. MODERATE
CONFIDENCE.
OUTLOOK...
TUESDAY THROUGH TUESDAY NIGHT...PERIODS OF MVFR AND IFR CONDITIONS
WITH RAIN LATE DAY TUESDAY BUT ESPECIALLY TUESDAY NIGHT.
WEDNESDAY THROUGH FRIDAY...MAINLY VFR BUT WITH WESTERLY WINDS GUSTS
30 TO 35 KNOTS LIKELY WEDNESDAY AND THURSDAY.
MARINE
A SMALL CRAFT ADVISORY REMAINS IN IN EFFECT FOR THE ATLANTIC
COASTAL WATERS THROUGH TONIGHT. SOUTH TO SOUTHWEST WINDS WILL
CONTINUE TO DIMINISH EARLY THIS MORNING AS A LOW-LEVEL JET HAS
SHIFTED TO OUR EAST AND THEN IN THE WAKE OF A COLD FRONT. SEAS
5-7 FEET ACROSS OUR OCEAN ZONES HOWEVER WILL TAKE SOME TIME TO
SUBSIDE. FOR DELAWARE BAY, THE CONDITIONS ARE EXPECTED TO REMAIN
BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH TONIGHT.
OUTLOOK...
TUESDAY...ONCE SEAS SUBSIDE EARLY TUE MORNING, WINDS AND SEAS SHOULD
STAY BELOW SCA CRITERIA THROUGH THE DAY TIME ON TUESDAY.
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...SCA CONDITIONS ARE LIKELY
TUESDAY NIGHT WITH THE POTENTIAL FOR GALE CONDITIONS WEDNESDAY AND
WEDNESDAY NIGHT.
THURSDAY AND FRIDAY...WINDS AND SEAS WILL BE SUBSIDING DURING THIS
PERIOD BUT CONDITIONS COULD STILL BE AT SMALL CRAFT ADVISORY LEVELS
THROUGH THURSDAY AND MUCH OF THURSDAY NIGHT.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 AM EST TUESDAY FOR ANZ450>455.
SYNOPSIS...FITZSIMMONS/GORSE
NEAR TERM...GORSE/MPS
SHORT TERM...FITZSIMMONS
LONG TERM...COOPER/FITZSIMMONS
AVIATION...FITZSIMMONS/GORSE/MPS
MARINE...FITZSIMMONS/GORSE
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