953
FXUS61 KPHI 131959
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
359 PM EDT TUE OCT 13 2026
WHAT HAS CHANGED
UPDATED KEY MESSAGE 1 AND THE AVIATION SECTION FOR THE 18Z
TAFS.
INCREASING POTENTIAL FOR STRONG WINDS WITH A COLD FRONT PASSAGE
ON FRIDAY.
INCREASING POTENTIAL FOR WIDESPREAD FROST AND FREEZE CONDITIONS
FOR SATURDAY NIGHT.
KEY MESSAGES
1. SURGE OF WARMTH AND HUMIDITY THROUGH WEDNESDAY AHEAD OF A
COLD FRONT.
2. A STRONG COLD FRONT PASSAGE ON FRIDAY WILL BRING WINDY
CONDITIONS, SHOWERS AND POTENTIAL FOR SOME THUNDERSTORMS, AND
COLDER TEMPERATURES INTO THE WEEKEND.
3. THERE IS POTENTIAL FOR WIDESPREAD FROST AND FREEZE CONDITIONS
SATURDAY NIGHT.
DISCUSSION
KEY MESSAGE 1...SURGE OF WARMTH AND HUMIDITY THROUGH WEDNESDAY
AHEAD OF A COLD FRONT.
A FRONTAL ZONE DRAPED TO OUR NORTH TODAY WILL RESULT IN SURFACE
LOW PRESSURE RIDING ALONG IT THROUGH WEDNESDAY, PULLING A COLD
FRONT ACROSS OUR AREA BY LATER WEDNESDAY. AHEAD OF THIS FEATURE,
SOUTHERLY FLOW WILL BOOST THE LOW-LEVEL WARM AIR ADVECTION
REGIME, RESULTING IN MUCH WARMER AIR SURGING INTO OUR AREA
THROUGH WEDNESDAY. HIGH TEMPERATURES WILL BE IN THE UPPER 70S TO
AROUND 80 DEGREES FOR MANY AREAS TODAY. WEDNESDAY'S HIGHS ARE
FORECAST TO MAINLY RANGE IN THE LOW TO MID 80S, WITH EVEN SOME
UPPER 80S TO NEAR 90 DEGREES POSSIBLE OVER SOUTHERN DELAWARE.
IN ADDITION, DEW POINTS WILL INCREASE BACK THROUGH THE 60S INTO
WEDNESDAY. THIS WILL RESULT IN A MUCH MORE HUMID FEEL OVER THE
NEXT COUPLE DAYS, WITH IT BEING THE MOST HUMID ON WEDNESDAY
(HEAT INDEX VALUES SHOULD APPROACH 90F FOR AREAS FROM ABOUT
PHILADELPHIA SOUTH AND EAST; AWAY FROM THE COAST). THERE DOES
NOT APPEAR TO BE MUCH IN THE WAY OF FORCING, THEREFORE JUST A
SLIGHT CHANCE (LESS THAN 25%) FOR SHOWERS IS EXPECTED. AFTER THE
FRONT MOVES THROUGH, COOLER AIR WILL BRIEFLY RETURN ON
THURSDAY.
KEY MESSAGE 2...A STRONG COLD FRONT PASSAGE ON FRIDAY WILL
BRING WINDY CONDITIONS, SHOWERS AND POTENTIAL FOR SOME
THUNDERSTORMS, AND COLDER TEMPERATURES INTO THE WEEKEND.
A SHARP UPPER-LEVEL TROUGH IS FORECAST TO ARRIVE ACROSS THE
EAST COAST ON FRIDAY, THEN GRADUALLY LIFT OUT OVER THE WEEKEND.
THIS WILL DRIVE RAPIDLY STRENGTHENING SURFACE LOW PRESSURE JUST
NORTH OF OUR AREA FRIDAY, WITH AN ASSOCIATED STRONG COLD FRONT
SWEEPING THROUGH. GUIDANCE HAS COME INTO CONSENSUS THAT THE FAST
MOVING COLD FRONTAL PASSAGE WILL OCCUR BETWEEN THE MID
AFTERNOON TO EVENING HOURS LIKELY MOVING FROM OUR WESTERN MOST
ZONES AND OFFSHORE WITHIN ABOUT 3 HOURS OR SO.
A WARM AND INCREASINGLY MOIST AIRMASS AHEAD OF THIS SYSTEM WILL
PROVIDE MODEST INSTABILITY AND DECENT BOUNDARY LAYER MIXING AS
THE STRONG COLD FRONT APPROACHES ON FRIDAY. LARGE SCALE FORCING
FOR ASCENT WILL INCREASE WITH THE ARRIVAL OF THE ROBUST UPPER-
LEVEL TROUGH AND COLD FRONT, THEREFORE SHOWERS WILL INCREASE IN
COVERAGE AND INTENSITY THURSDAY NIGHT INTO FRIDAY. HOWEVER, THE
EXACT DETAILS REGARDING THE CONVECTIVE EVOLUTION REMAIN UNCLEAR.
SOME THUNDERSTORMS ARE POSSIBLE GIVEN THE STRENGTH OF THE
SYSTEM AND INSTABILITY, HOWEVER THIS WILL ULTIMATELY DEPEND ON
THE MAGNITUDE OF THE INSTABILITY AND TIMING OF THE COLD FRONT.
CANNOT RULE OUT SOME SEVERE THUNDERSTORM POTENTIAL, ESPECIALLY
IF ANY MORE ROBUST CONVECTION CAN MATERIALIZE ALONG THE COLD
FRONT.
WHILE IT WILL BE MOSTLY CLOUDY, STRONG WARM ADVECTION WILL BOOST
TEMPERATURES UP WELL INTO THE 70S AND LOW 80S AHEAD OF THE
FRONT. AS SURFACE PRESSURE FALLS RAPIDLY AMID A STRENGTHENING
SOUTHWESTERLY GRADIENT, BREEZY CONDITIONS WILL LIKELY DEVELOP
OUTSIDE OF ANY SHOWERS AND STORMS WITH GUSTS OF 25-35 MPH
POSSIBLE.
DURING AND AFTER COLD FRONTAL PASSAGE, STRONG COLD AIR
ADVECTION WILL OCCUR AS THE SHARP TROUGH ALOFT SWEEPS THROUGH.
THIS WILL SUPPORT EFFICIENT MIXING OF WINDS ALOFT DOWN TOWARD
THE SURFACE IN THE FORM OF FREQUENT WIND GUSTS AS TEMPERATURES
PLUMMET INTO THE 50S THEN 40S OVERNIGHT. BOUNDARY LAYER WINDS
COULD BE AS HIGH AS 40 KTS INLAND, WHICH COULD TRANSLATE TO A
PERIOD OF NORTHWEST WINDS GUSTING 40-50 MPH FOR A FEW HOURS IN
THE WAKE OF THE FRONT. THE TIMING OF THE PEAK WINDS APPEARS TO
BE FOCUSED DURING THE EVENING AND EARLY OVERNIGHT HOURS,
DIMINISHING SOME AFTER MIDNIGHT FRIDAY NIGHT.
THE COLDEST AIRMASS SO FAR THIS SEASON WILL SETTLE INTO THE AREA
SATURDAY INTO SATURDAY NIGHT. HIGH TEMPERATURES SATURDAY ARE
ONLY IN THE LOW TO MID 50S IN MOST AREAS (40S NORTH OF I-78).
BREEZY CONDITIONS WILL CONTINUE, WITH NORTHWEST WINDS GUSTING
30-40 MPH POSSIBLE IN THE MORNING BEFORE GRADUALLY DIMINISHING
LATER IN THE DAY.
KEY MESSAGE 3...THERE IS POTENTIAL FOR WIDESPREAD FROST AND
FREEZE CONDITIONS SATURDAY NIGHT.
AS STRONG SURFACE HIGH PRESSURE SETTLES NEARLY OVERHEAD INTO
SATURDAY NIGHT, TEMPERATURES WILL COOL SIGNIFICANTLY WITH
RADIATIONAL COOLING. THIS SHOULD RESULT IN WIDESPREAD LOW
TEMPERATURES IN THE 30S SATURDAY NIGHT INTO SUNDAY MORNING, AND
POTENTIALLY INTO THE UPPER 20S NORTH OF I-78. THIS WILL
INTRODUCE OUR FIRST WIDESPREAD FROST AND FREEZE POTENTIAL OF THE
SEASON. A FREEZE APPEARS UNLIKELY SOUTH OF I-78, BUT THE USUAL
COLD SPOTS COULD DROP TO NEAR THE FREEZING MARK. OTHERWISE,
AREAS OF FROST ARE POSSIBLE.
THE AIRMASS WILL START TO MODIFY SUNDAY AND INTO EARLY NEXT
WEEK. HIGHS SUNDAY SHOULD REBOUND INTO THE MID 50S TO NEAR 60
DEGREES IN MOST AREAS WITH WINDS 5-10 MPH MAKING FOR A MUCH MORE
PLEASANT DAY COMPARED TO SATURDAY. THERE COULD BE SOME FROST
POTENTIAL SUNDAY NIGHT, BUT LOWS ARE LIKELY TO REBOUND INTO THE
UPPER 30S TO LOW 40S IN MOST AREAS. TEMPERATURES WILL THEN
REBOUND TO NEAR NORMAL VALUES, WITH HIGHS WELL INTO THE 60S
EARLY NEXT WEEK AND DRY WEATHER EXPECTED.
AVIATION /19Z TUESDAY THROUGH SUNDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
REST OF TODAY... VFR WITH MAINLY CLEAR SKIES. SOUTHWEST WINDS
AROUND 10 KT. HIGH CONFIDENCE.
TONIGHT...VFR WITH MOSTLY CLEAR SKIES. A PERIOD OF LLWS IS
POSSIBLE MAINLY BETWEEN 00Z-08Z. WEST-SOUTHWEST WINDS 4-8 KT.
HIGH CONFIDENCE.
WEDNESDAY...VFR WITH INCREASING CLOUDS AFTER DAYBREAK. WEST
WINDS AROUND 5-10 KT EARLY, INCREASING TO 10-15 KT IN THE
AFTERNOON. A PERIOD OF SHOWERS IS POSSIBLE FROM WEST TO EAST,
BUT CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE IN TAFS AT THIS
TIME. MODERATE-HIGH CONFIDENCE OVERALL.
OUTLOOK...
WEDNESDAY NIGHT...VFR. SLIGHT CHANCE FOR BRIEF RESTRICTIONS IN
SHOWERS.
THURSDAY AND FRIDAY...PERIODS OF RESTRICTIONS PROBABLE DURING
THIS PERIOD, ESPECIALLY ON FRIDAY IN SHOWERS. POTENTIAL FOR
THUNDERSTORMS AS WELL. SOUTHWEST WINDS FRIDAY SHIFTING
NORTHWEST FRIDAY EVENING WITH GUSTS UP TO 40 KTS POSSIBLE.
SATURDAY THROUGH SUNDAY...VFR. NORTHWEST WINDS GUSTING UP TO 30
KTS ON SATURDAY.
MARINE
NO MARINE HEADLINES ARE IN EFFECT THROUGH WEDNESDAY. SOUTH-
SOUTHWEST WINDS ARE EXPECTED TO INCREASE TO AROUND 15-20 KT
LATER THIS AFTERNOON THROUGH TONIGHT WITH GUSTS UP TO 22-23 KT
POSSIBLE. WINDS WILL BECOME WEST AROUND 10-15 KT ON WEDNESDAY
FOLLOWING A COLD FRONTAL PASSAGE. SEAS AROUND 2-4 FEET. FAIR
WEATHER EXPECTED OUTSIDE OF GUSTY WINDS.
OUTLOOK...
WEDNESDAY NIGHT THROUGH THURSDAY...NO MARINE HAZARDS ARE
ANTICIPATED.
FRIDAY AND SATURDAY...SMALL CRAFT ADVISORY CONDITIONS DEVELOPING
DURING THE DAYTIME FRIDAY, THEN GALE FORCE WINDS LIKELY FRIDAY
NIGHT INTO SATURDAY AS A STRONG COLD FRONT PUSHES OFFSHORE
FRIDAY EVENING. SEAS BUILDING OVER 5 FEET.
SATURDAY NIGHT THROUGH SUNDAY...NO MARINE HAZARDS ARE
ANTICIPATED.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.
DISCUSSION...DESILVA/MJL/STAARMANN
AVIATION...DESILVA/STAARMANN
MARINE...DESILVA/STAARMANN
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page