792
FXUS61 KPHI 201056
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
656 AM EDT WED MAY 20 2026
WHAT HAS CHANGED
NO SIGNIFICANT CHANGES.
KEY MESSAGES
1. HOT AND HUMID CONDITIONS CONTINUE, WITH RECORD SETTING EARLY
SEASON HEAT PROBABLE, THROUGH TODAY.
2. A STRONG COLD FRONT BRINGS SOME SHOWERS AND POSSIBLY ISOLATED
SEVERE THUNDERSTORMS TO THE REGION THIS AFTERNOON AND EVENING.
3. SIGNIFICANTLY COOLER TEMPERATURES AND SEVERAL ROUNDS OF 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 TODAY.
A STRONG UPPER-LEVEL RIDGE CENTERED OFF THE SOUTHEAST U.S. COAST
STARTS TO FLATTEN ON ITS NORTHWEST SIDE TODAY. THOUGH, WITH
SURFACE HIGH PRESSURE ANCHORED IN THE WESTERN ATLANTIC A
SOUTHWESTERLY FLOW OF EARLY SEASON (ANOMALOUS) HEAT WILL
CONTINUE TO FLOW ACROSS OUR AREA TODAY.
TEMPERATURES PEAK IN THE 90S FOR MANY AREAS AGAIN THIS AFTERNOON,
EXCEPT COOLER ALONG THE COASTS AND THE HIGHER TERRAIN. HOW
QUICKLY CLOUD COVER ARRIVES, ALONG WITH SHOWERS AND SOME
THUNDERSTORMS FROM AN APPROACHING COLD FRONT, WILL ALSO
IMPACT HIGH TEMPERATURES TODAY, ESPECIALLY NORTH AND WEST OF
I-95. EITHER WAY THOUGH, WE WILL HAVE A HIGH LAUNCHING PAD
ONCE AGAIN FOR TEMPERATURES, WITH LOWS THIS MORNING ONLY IN THE
UPPER 60S TO LOW 70S, SO IT WILL STILL BE RATHER HOT THIS
AFTERNOON. 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. PEAK HEAT INDICES WILL BE NEAR 100
DEGREES, WITH THE CORE OF THE HEAT SHIFTING A BIT MORE SOUTH
AND EAST TODAY AS THE STRONG COLD FRONT STARTS TO ARRIVE.
THE HEAT ADVISORY REMAINS IN PLACE FOR ACROSS MUCH OF THE
REGION THROUGH 8 PM THIS EVENING. WHILE SOME AREAS WILL
PROBABLY FALL A LITTLE SHORT OF CRITERIA, PARTICULARLY IN BERKS
COUNTY, THE LEHIGH VALLEY, AND INTO NORTHERN NEW JERSEY WHERE
IT WILL BE COOLER TODAY AHEAD OF THE APPROACHING FRONT, IT WILL
STILL BE ANOTHER HOT AND HUMID DAY REGARDLESS. THE POTENTIAL FOR
GREATER IMPACTS, DUE TO LACK OF ACCLIMATION THIS EARLY IN THE
SEASON AND THE ACCUMULATIVE EFFECT WITH THIS BEING THE THIRD
STRAIGHT DAY OF HIGH HEAT, CONTINUES TO DRIVE OUR DECISION.
ALONG THE IMMEDIATE COAST, 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 THESE AREAS IN THE HEAT ADVISORY.
KEY MESSAGE 2...A STRONG COLD FRONT BRINGS SOME SHOWERS AND
POSSIBLY ISOLATED SEVERE THUNDERSTORMS TO THE REGION THIS
AFTERNOON AND EVENING.
A STRONG COLD FRONT WILL SETTLE ACROSS OUR AREA THIS AFTERNOON
AND TONIGHT 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 THIS 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 THIS
EVENING, WITH SOME SHOWERS LINGERING IN THE WAKE OF THE COLD
FRONT.
KEY MESSAGE 3...SIGNIFICANTLY COOLER TEMPERATURES AND SEVERAL
ROUNDS OF 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.
FURTHERMORE, WITH PWAT VALUES AROUND 1.50-1.90 INCHES OVER THE
WEEKEND, WHICH IS AROUND THE CLIMATOLOGICAL MAXIMUM FOR THIS
TIME OF THE YEAR, THERE IS AT LEAST A MARGINAL CHANCE FOR
EXCESSIVE RAINFALL ON SATURDAY. WE WILL BE KEEPING AN EYE ON HOW
STRONG THE BAROCLINIC FORCING GETS ALONG THE STALLED BOUNDARY
WEDGED BETWEEN THE HIGH TO THE NORTHEAST AND THE LOW TO THE WEST.
NORTHEAST FLOW ALONG WITH SEVERAL ROUNDS OF SHOWERS 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 /12Z WEDNESDAY THROUGH SUNDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
TODAY...VFR OVERALL WITH INCREASING CLOUDS DURING THE DAY. SOME
SHOWERS AND THUNDERSTORMS ARRIVE AFTER 19Z 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.
TONIGHT...MVFR CONDITIONS POSSIBLE WITH FOG/LOW STRATUS,
PARTICULARLY AT TERMINALS WHICH RECEIVE SHOWERS/STORMS THIS
EVENING. SOME LINGERING SHOWERS MAY ALSO CONTRIBUTE TO SUB-VFR
CONDITIONS, PARTICULARLY AT KMIV AND KACY. NORTHERLY WINDS
AROUND 5 KNOTS. LOW CONFIDENCE.
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 TODAY,
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 TODAY, IT IS VERY MARGINAL AND
THEREFORE LARGELY SUB-SCA CONDITIONS ARE EXPECTED. THERE IS THE
POTENTIAL FOR ISOLATED GUSTY THUNDERSTORMS LATE THIS AFTERNOON
AND ESPECIALLY THIS EVENING.
OUTLOOK...
THURSDAY...SMALL CRAFT ADVISORY CONDITIONS ARE POSSIBLE WITH
NORTHEAST WINDS GUSTING AROUND 20KTS.
FRIDAY AND SATURDAY...SMALL CRAFT ADVISORY CONDITIONS SHOULD OCCUR.
SUNDAY...SEAS MAY LINGER AROUND 4 TO 6 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
RECORD-SETTING TEMPERATURES OCCURRED ON TUESDAY, MAY 19TH. BELOW
IS A SUMMARY OF RECORDS THAT WERE TIED OR BROKEN.
RECORD HIGH TEMPERATURES BROKEN ON MAY 19TH
SITE RECORD/YEAR
PHILADELPHIA (PHL) 96/1962 (NEW RECORD 98*)
READING (RDG) 96/1962 (NEW RECORD 97*)
TRENTON (TTN) 96/1962 (RECORD TIED)
WILMINGTON (ILG) 95/1962 (NEW RECORD 96)
*THE RECORD HIGH OF 98 AT PHILADELPHIA (PHL) AND 97 AT READING
(RDG) ALSO BREAKS OR TIES THE ALL TIME RECORD HIGH FOR THE
MONTH OF MAY AT BOTH SITES.
RECORD WARMEST LOW TEMPERATURES BROKEN ON MAY 19TH
SITE RECORD/YEAR
ALLENTOWN (ABE) 65/2017 (RECORD TIED)
MOUNT POCONO (MPO) 60/1943 (NEW RECORD 66)
READING (RDG) 68/1962 (NEW RECORD 72*)
*THE RECORD WARMEST LOW OF 72 AT READING (RDG) ALSO TIED THE ALL
TIME RECORD WARMEST LOW OF 72 FOR THE MONTH OF MAY, SET BACK ON
MAY 28 & 31, 1939 AND MAY 31, 1991.
MORE RECORD BREAKING TEMPERATURES ARE POSSIBLE 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) 98/MAY 19, 2026 (NEW)
READING (RDG) 97/MAY 20, 1996 & MAY 19, 2026
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, & MAY 19, 2026
TRENTON (TTN) 75/MAY 31, 1895
WILMINGTON (ILG) 75/MAY 30, 1895
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(TIES)
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 THIS EVENING FOR PAZ060>062-070-
071-101>106.
NJ...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR NJZ007>010-012-
013-015-017>020-027.
DE...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR DEZ001.
MD...NONE.
MARINE...NONE.
DISCUSSION...AKL/GORSE/MJL
AVIATION...AKL/MJL
MARINE...AKL/MJL/MPS
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