979
FXUS61 KPHI 192012
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
412 PM EDT TUE MAY 19 2026
WHAT HAS CHANGED
ALL OF THE HEAT ADVISORY NOW IN EFFECT THROUGH 8 PM WEDNESDAY.
AN ISOLATED STRONG TO SEVERE THUNDERSTORM POSSIBLE THROUGH EARLY
THIS EVENING MAINLY NORTH/WEST OF I-95.
SMALL CRAFT ADVISORY HAS BEEN CANCELLED.
KEY MESSAGES
1. HOT AND HUMID CONDITIONS CONTINUE, WITH RECORD SETTING EARLY
SEASON HEAT PROBABLE, THROUGH WEDNESDAY.
2. A STRONG COLD FRONT BRINGS SOME SHOWERS AND POSSIBLY ISOLATED
SEVERE THUNDERSTORMS TO THE REGION WEDNESDAY AFTERNOON AND EVENING.
3. SIGNIFICANTLY COOLER TEMPERATURES AND SHOWERS FOR THE END OF
THIS WEEK AND THE HOLIDAY WEEKEND.
DISCUSSION
KEY MESSAGE 1...HOT AND HUMID CONDITIONS CONTINUE, WITH RECORD
SETTING EARLY SEASON HEAT PROBABLE, THROUGH WEDNESDAY.
A STRONG UPPER-LEVEL RIDGE CENTERED OFF THE SOUTHEAST U.S.
COAST WILL REMAIN IN PLACE THROUGH TONIGHT BEFORE IT STARTS TO
FLATTEN ON ITS NORTHWEST SIDE DURING WEDNESDAY. THIS ALONG WITH
SURFACE HIGH PRESSURE ANCHORED IN THE WESTERN ATLANTIC WILL
CONTINUE TO DRIVE A SOUTHWESTERLY FLOW OF EARLY SEASON
(ANOMALOUS) HEAT ACROSS OUR AREA THROUGH WEDNESDAY.
TEMPERATURES PEAK IN THE 90S FOR MANY AREAS AGAIN THIS
AFTERNOON AND AGAIN WEDNESDAY AFTERNOON, EXCEPT COOLER ALONG THE
COASTS AND THE HIGHER TERRAIN. WHILE THE SURFACE DEW POINTS
WILL MIX OUT SOME DURING PEAK HEATING THIS AFTERNOON DUE TO THE
DRIER GROUND AND BOUNDARY LAYER, THIS STRETCH OF EARLY SEASON
HEAT, WITH ADDITIONAL RECORD BREAKING HIGH TEMPERATURES
PROBABLE, WILL HAVE POTENTIALLY GREATER IMPACTS. THE HEAT
ADVISORY REMAINS IN PLACE ACROSS MUCH OF THE REGION, WHERE THE
HEAT INDEX CRITERIA STARTS AT 100F (THE URBAN I-95 CORRIDOR
CRITERIA STARTS AT 96F THROUGH JUNE). WHILE SOME AREAS WILL
PROBABLY FALL A LITTLE SHORT, THE POTENTIAL FOR GREATER IMPACTS
(LACK OF ACCLIMATION) CONTINUES TO DRIVE OUR DECISION. WHERE THE
WIND TURNS MORE FROM THE SOUTH AND ESPECIALLY SOUTHEAST WILL
RESULT IN QUITE A BIT OF COOLING DUE TO THE CHILLY OCEAN AND
THEREFORE CONTINUED TO NOT INCLUDE THE IMMEDIATE COASTAL ZONES
IN THE HEAT ADVISORY. PEAK HEAT INDICES WILL BE NEAR 100
DEGREES, WITH THE CORE OF THE HEAT SHIFTING A BIT MORE SOUTH AND
EAST DURING WEDNESDAY AS A STRONG COLD FRONT STARTS TO ARRIVE.
DESPITE IT BEING A LITTLE COOLER FROM BERKS COUNTY, THE LEHIGH
VALLEY INTO NORTHERN NEW JERSEY WEDNESDAY, IT WILL BE ANOTHER
DAY OF HOT AND HUMID CONDITIONS. GIVEN THE CONSECUTIVE STRETCH
OF THIS EARLY SEASON HEAT, OPTED TO CONTINUE THE CURRENT HEAT
ADVISORY THROUGH 8 PM WEDNESDAY BUT EXTENDED THE FAR NORTH AND
WEST SEGMENT (ALSO THROUGH 8 PM WEDNESDAY). HIGH TEMPERATURES ON
WEDNESDAY WILL DEPEND ON HOW QUICKLY CLOUD COVER ARRIVES ALONG
WITH SHOWERS AND SOME THUNDERSTORMS, ESPECIALLY NORTH AND WEST
OF I-95. EITHER WAY, WE WILL HAVE A HIGH LAUNCHING PAD ONCE
AGAIN FOR TEMPERATURES TO START WEDNESDAY AND IT WILL STILL BE
RATHER HOT.
THIS AFTERNOON AND INTO THIS EVENING WILL MAINLY PRECIPITATION-
FREE, HOWEVER AN ISOLATED SHOWER OR THUNDERSTORM CANNOT BE RULED
OUT MAINLY NORTH AND WEST OF I-95 GIVEN THE AMOUNT OF HEAT AND
INSTABILITY COMBINED WITH A THERMAL TROUGH NEARBY. THIS WOULD
MOST LIKELY BE TERRAIN INDUCED OR ISOLATED ACTIVITY ARRIVING
FROM THE WEST. GIVEN STEEP LOW-LEVEL LAPSE RATES, DRY BOUNDARY
LAYER (HIGH DCAPE) BUT RATHER WEAK FORCING, ANY CONVECTION
SHOULD BE SHORT-LIVED AND PULSE VARIETY WITH LOCALLY GUSTY WINDS
(DOWNBURSTS) POSSIBLE.
KEY MESSAGE 2...A STRONG COLD FRONT BRINGS SOME SHOWERS AND
POSSIBLY ISOLATED SEVERE THUNDERSTORMS TO THE REGION WEDNESDAY
AFTERNOON AND EVENING.
A STRONG COLD FRONT WILL SETTLE ACROSS OUR AREA WEDNESDAY
AFTERNOON AND WEDNESDAY NIGHT BEFORE STALLING NEAR DELMARVA INTO
THURSDAY. SHOWERS AND SOME THUNDERSTORMS WILL DEVELOP AHEAD OF
THE FRONT, AND THERE LOOKS TO BE A ZONE OF HIGHER INSTABILITY
ACROSS OUR CENTRAL AND SOUTHERN ZONES WEDNESDAY AFTERNOON. IT IS
IN THESE AREAS WHERE CONVECTION MAY TRY TO ORGANIZE A BIT MORE
AS IT DEVELOPS EASTWARD AND ENCOUNTERS PLENTY OF INSTABILITY.
THE DEEP-LAYER SHEAR IS ON THE MARGINAL SIDE (STRONGEST SHEAR TO
OUR NORTHWEST) AS ARE THE MID LEVEL LAPSE RATES, HOWEVER A HOT
BOUNDARY LAYER WILL RESULT IN STEEP LOW-LEVEL LAPSE RATES. THE
COMBINATION OF THE STEEP LOW-LEVEL LAPSE RATES AND ANY STRONGER
CONVECTIVE CORES, LOCALLY STRONG TO DAMAGING WINDS (DOWNBURSTS)
WILL BE POSSIBLE.
DUE TO THE LOWER SHEAR CONVECTION MAY STRUGGLE TO ORGANIZE,
HOWEVER GIVEN THE HOT AIR MASS IN PLACE SOME LINEAR OR SMALL
CLUSTERING COULD DEVELOP FROM ABOUT THE PHILADELPHIA METRO ON
SOUTH AND EASTWARD LATE IN THE AFTERNOON AND EVENING. THE
COVERAGE OF STRONGER CONVECTION IS OF LOWER CONFIDENCE, HOWEVER
GIVEN THE LOWER SHEAR VALUES THE SEVERE THUNDERSTORM RISK LOOKS
ISOLATED. GENERAL RAINFALL TOTALS ARE 0.10- 0.50 INCHES, HOWEVER
GIVEN PRECIPITABLE WATER VALUES OF 1.5-2.0 INCHES, LOCALIZED
HIGHER AMOUNTS ARE QUITE POSSIBLE WITH ANY STRONGER SHOWERS OR
THUNDERSTORMS. ANY THUNDERSTORMS SHOULD END BY LATE WEDNESDAY
EVENING, WITH SOME SHOWERS LINGERING IN THE WAKE OF THE COLD
FRONT.
KEY MESSAGE 3...SIGNIFICANTLY COOLER TEMPERATURES AND SHOWERS
FOR THE END OF THIS WEEK AND THE HOLIDAY WEEKEND.
A COLD FRONT IS FORECAST TO SETTLE AND THEN STALL TO OUR SOUTH
THURSDAY AND INTO THE HOLIDAY WEEKEND. SOME RIPPLES OF ENERGY
RIDE ALONG AND NORTH OF IT AND THIS LOOKS TO BRING SOME ROUNDS
OF SHOWERS TO OUR REGION. A MORE ORGANIZED SURFACE LOW WELL TO
OUR WEST MAY PROVIDE AN INCREASE IN SHOWERS OR A PERIOD OF RAIN
LATER FRIDAY AND SATURDAY. THE PRECIPITATION MAY BECOME ENHANCED
SOME AS SURFACE HIGH PRESSURE TO OUR NORTHEAST WEDGES
SOUTHWESTWARD INTO OUR AREA CREATING SOME COOL AIR DAMMING. THIS
WILL ALL RESULT IN MUCH COOLER TEMPERATURES THURSDAY THROUGH
SATURDAY, THEN SOME WARMING SHOULD TAKE PLACE SUNDAY AND INTO
MEMORIAL DAY. THE PATTERN LOOKS ACTIVE THOUGH AND THEREFORE SOME
ADDITIONAL SHOWERS ARE QUITE POSSIBLE RIGHT INTO MEMORIAL DAY.
WHILE NOT GREAT TIMING, OUR REGION NEEDS RAIN AS A LONG-TERM
DROUGHT CONTINUES.
AVIATION /20Z TUESDAY THROUGH SUNDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
THIS AFTERNOON...VFR. AN ISOLATED SHOWER OR THUNDERSTORM CANNOT
BE RULED OUT TOWARD EVENING MAINLY NORTH AND WEST OF KPHL.
SOUTHWESTERLY WINDS 8-12 KNOTS WITH SOME GUSTS TO 20 KNOTS. LOW
CONFIDENCE REGARDING SHOWER/THUNDERSTORM OCCURRENCE.
TONIGHT...VFR. SOUTHWEST WINDS 5-10 KNOTS, BECOMING LOCALLY
LIGHT AND VARIABLE. MODERATE CONFIDENCE.
WEDNESDAY...VFR OVERALL WITH INCREASING CLOUDS DURING THE DAY.
SOME SHOWERS AND THUNDERSTORMS ARRIVE LATER IN THE AFTERNOON AND
EVENING WITH AREAS OF SUB-VFR CONDITIONS. LOCALLY GUSTY WINDS
POSSIBLE WITH A STRONGER THUNDERSTORM. SOUTHWEST WINDS
INCREASING TO 10-15 KNOTS WITH SOME GUSTS TO 20 KNOTS. LOW
CONFIDENCE ON TIMING DETAILS.
OUTLOOK...
THURSDAY...A PERIOD OF SUB-VFR CONDITIONS WITH SOME SHOWERS.
FRIDAY THROUGH SUNDAY...PERIODS OF SUB-VFR CONDITIONS WITH
SHOWERS AT TIMES, ESPECIALLY LATE FRIDAY AND SATURDAY.
MARINE
SOUTHERLY WINDS WILL BE GUSTY, TO 20 KNOTS, THROUGH WEDNESDAY,
HOWEVER A HOT AIR MASS OVER THE CHILLY OCEAN WATER IS RESULTING
IN A VERY STRONG INVERSION JUST ABOUT THE SURFACE. THIS IS
LIMITING THE VERTICAL MIXING. WHILE SEAS IN THE SOUTHERLY FLOW
COULD BUILD TO 5 FEET THROUGH WEDNESDAY, IT IS VERY MARGINAL AND
THEREFORE THE SMALL CRAFT ADVISORY WAS CANCELLED. THERE IS THE
POTENTIAL FOR ISOLATED GUSTY THUNDERSTORMS LATE WEDNESDAY
AFTERNOON AND ESPECIALLY WEDNESDAY EVENING.
OUTLOOK...
THURSDAY...THE CONDITIONS ARE ANTICIPATED TO BE BELOW SMALL CRAFT
ADVISORY CRITERIA.
FRIDAY AND SATURDAY...SMALL CRAFT ADVISORY CONDITIONS SHOULD OCCUR.
SUNDAY...SEAS MAY LINGER AROUND 5 FEET, OTHERWISE THE CONDITIONS
SHOULD BE BELOW SMALL CRAFT ADVISORY CRITERIA.
RIP CURRENTS...
ON WEDNESDAY, SOUTH TO SOUTHWEST WINDS WILL RANGE FROM 10 TO 15
MPH WITH GUSTS UP TO 20 MPH. THERE WILL BE A SOUTHEAST SWELL
WITH A PERIOD AROUND 6 SECONDS. AS A RESULT, THERE IS A MODERATE
RISK FOR THE DEVELOPMENT OF DANGEROUS RIP CURRENTS FOR THE
JERSEY SHORE AND A LOW RISK FOR DELAWARE BEACHES.
ON THURSDAY, WINDS BECOME NORTHEAST 10 TO 15 MPH AT THE JERSEY
SHORE IN MONMOUTH COUNTY, AND 15 TO 20 MPH AT THE REST OF THE
JERSEY SHORE AND AT DELAWARE BEACHES. THERE WILL BE A SOUTHERLY
SWELL WITH A PERIOD AROUND 6 SECONDS. BREAKING WAVES WILL BE 1
TO 3 FEET. AS A RESULT, THERE IS A LOW RISK FOR THE DEVELOPMENT
OF DANGEROUS AND LIFE THREATENING RIP CURRENTS AT THE JERSEY
SHORE IN MONMOUTH COUNTY AND A MODERATE RISK FOR THE REST OF THE
JERSEY SHORE AND DELAWARE BEACHES.
SURFACE TEMPERATURES INLAND WILL BE IN THE 90S AGAIN ON
WEDNESDAY, TEMPERATURES ALONG THE COASTS WILL MAINLY BE IN THE
70S TO NEAR 80 DUE TO OCEAN TEMPERATURES IN THE 50S. THESE COLD
WATER TEMPERATURES CAN QUICKLY CAUSE HYPOTHERMIA AND PHYSICAL
INCAPACITATION TO ANYONE SUDDENLY IMMERSED IN THE WATER.
FOR SPECIFIC BEACH FORECASTS, VISIT WEATHER.GOV/BEACH/PHI
CLIMATE
SOME RECORD BREAKING TEMPERATURES ARE FORECAST THROUGH WEDNESDAY.
HIGH TEMPERATURES TODAY AND LOW TEMPERATURES WEDNESDAY MORNING
COULD CHALLENGE MONTHLY ALL TIME RECORDS FOR MAY.
RECORDS FOR OUR CLIMATE SITES ARE LISTED BELOW:
MONTHLY RECORD HIGH TEMPERATURES FOR MAY
SITE RECORD/DATE
ALLENTOWN (ABE) 97/MAY 19, 1962
AC AIRPORT (ACY) 99/MAY 29, 1969
AC MARINA (55N) 95/MAY 31, 1895 & MAY 23, 1925
GEORGETOWN (GED) 98/MAY 28, 1991
MOUNT POCONO (MPO) 94/MAY 22, 1911
PHILADELPHIA (PHL) 97/MAY 30 & 31, 1991
READING (RDG) 97/MAY 20, 1996
TRENTON (TTN) 99/MAY 23, 1911 & MAY 31, 1986
WILMINGTON (ILG) 98/MAY 10, 1895 & MAY 30, 1895
MONTHLY RECORD WARMEST LOW TEMPERATURES FOR MAY
SITE RECORD/DATE
ALLENTOWN (ABE) 71/MAY 31, 1975, MAY 28 & 31, 1991
AC AIRPORT (ACY) 73/MAY 24, 2004 & MAY 19, 2017
AC MARINA (55N) 73/MAY 30 & 31, 1987, & MAY 31, 1991
GEORGETOWN (GED) 74/MAY 23, 1953 & MAY 20, 2019
MOUNT POCONO (MPO) 68/MAY 21, 1996
PHILADELPHIA (PHL) 78/MAY 31, 1895
READING (RDG) 72/MAY 28 & 31, 1939, & MAY 31, 1991
TRENTON (TTN) 75/MAY 31, 1895
WILMINGTON (ILG) 75/MAY 30, 1895
RECORD HIGH TEMPERATURES
MAY 19
SITE RECORD/YEAR
ALLENTOWN (ABE) 97/1962
AC AIRPORT (ACY) 96/1962
AC MARINA (55N) 92/1998
GEORGETOWN (GED) 96/1962
MOUNT POCONO (MPO) 89/1962
PHILADELPHIA (PHL) 96/1962
READING (RDG) 96/1962
TRENTON (TTN) 96/1962
WILMINGTON (ILG) 95/1962
RECORD WARMEST LOW TEMPERATURES
MAY 19
SITE RECORD/YEAR
ALLENTOWN (ABE) 65/2017
AC AIRPORT (ACY) 73/2017
AC MARINA (55N) 68/1998
GEORGETOWN (GED) 73/2017
MOUNT POCONO (MPO) 60/1943
PHILADELPHIA (PHL) 74/1877
READING (RDG) 68/1962
TRENTON (TTN) 70/2017
WILMINGTON (ILG) 70/2017
RECORD HIGH TEMPERATURES
MAY 20
SITE RECORD/YEAR
ALLENTOWN (ABE) 92/1962 & 1996
AC AIRPORT (ACY) 96/1996
AC MARINA (55N) 93/1996
GEORGETOWN (GED) 95/1962
MOUNT POCONO (MPO) 89/1996
PHILADELPHIA (PHL) 94/1962 & 1996
READING (RDG) 97/1996
TRENTON (TTN) 94/1996
WILMINGTON (ILG) 96/1996
RECORD WARMEST LOW TEMPERATURES
MAY 20
SITE RECORD/YEAR
ALLENTOWN (ABE) 66/2019
AC AIRPORT (ACY) 68/1996
AC MARINA (55N) 69/1996
GEORGETOWN (GED) 74/2019
MOUNT POCONO (MPO) 61/1959
PHILADELPHIA (PHL) 71/2019
READING (RDG) 69/1959 & 1996
TRENTON (TTN) 68/1903, 1959, & 1962
WILMINGTON (ILG) 70/2019
PHI WATCHES/WARNINGS/ADVISORIES
PA...HEAT ADVISORY UNTIL 8 PM EDT WEDNESDAY FOR PAZ060>062-070-071-
101>106.
NJ...HEAT ADVISORY UNTIL 8 PM EDT WEDNESDAY FOR NJZ007>010-012-013-
015-017>020-027.
AIR QUALITY ALERT UNTIL 11 PM EDT THIS EVENING FOR NJZ012>021-
026-027.
DE...HEAT ADVISORY UNTIL 8 PM EDT WEDNESDAY FOR DEZ001.
MD...NONE.
MARINE...NONE.
DISCUSSION...GORSE
AVIATION...GORSE
MARINE...AKL/GORSE/MPS
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