500
FXUS61 KPHI 211042
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
642 AM EDT TUE JUL 21 2026
WHAT HAS CHANGED
UPDATED AVIATION SECTION FOR THE 12Z TAFS.
THE TIMING FOR THE SEVERE THUNDERSTORM RISK TODAY LOOKS TO BE
DELAYED SOME.
KEY MESSAGES
1. THERE CONTINUES TO BE AN ELEVATED RISK FOR SEVERE THUNDERSTORMS
AND FLASH FLOODING TODAY AND WEDNESDAY, WITH THE GREATER RISK THIS
AFTERNOON AND THIS EVENING.
DISCUSSION
KEY MESSAGE 1...THERE CONTINUES TO BE AN ELEVATED RISK FOR SEVERE
THUNDERSTORMS AND FLASH FLOODING TODAY AND WEDNESDAY, WITH THE
GREATER RISK THIS AFTERNOON AND THIS EVENING.
A STRONG UPPER-LEVEL TROUGH IS FORECAST TO PIVOT INTO AND ACROSS THE
NORTHEAST AND MID-ATLANTIC LATER THIS AFTERNOON AND TONIGHT, THEN
REMAIN IN PLACE THROUGH WEDNESDAY. THIS WILL DRIVE SURFACE LOW
PRESSURE WELL TO OUR NORTH, HOWEVER AN ASSOCIATED WARM FRONT WILL
LIFT NORTH ACROSS OUR REGION TODAY FOLLOWED BY A COLD FRONT LATE
THIS AFTERNOON AND TONIGHT.
AN INCREASE IN THE LOW-LEVEL WARM AIR ADVECTION THIS MORNING
WILL BE ENHANCED BY A SOUTHERLY LOW-LEVEL JET OF ABOUT 30 KNOTS.
THIS IS PROVIDING LIFT WITHIN A MOISTENING AIR MASS TO GENERATE
SOME SHOWERS AND THUNDERSTORMS THIS MORNING, WITH THIS MAINLY
FOCUSED NORTH AND WEST OF I-95. THERE IS SOME 850 MB CONVERGENCE
NORTH OF I-78 EARLY THIS MORNING, AND THIS IS WITHIN AN AXIS OF
INCREASING INSTABILITY. THIS IS LIKELY DRIVING THE ONGOING
CLUSTER OF CONVECTION MOVING NORTHEASTWARD ACROSS OUR FAR
NORTHWEST ZONES. THESE CELLS SHOULD BE FASTER MOVING THEREFORE
THE FLASH FLOOD RISK SHOULD REMAIN LIMITED. AS A WARM FRONT
ADVANCES NORTHWARD, INCREASING DEW POINTS AND AT LEAST SOME
SUNSHINE SHOULD PROMOTE PLENTY OF INSTABILITY THIS AFTERNOON AND
EVENING. THE NORTHWARD MOVEMENT OF THE WARM FRONT WILL
DETERMINE THE EXTENT OF THE GREATER INSTABILITY. THE LOW-LEVEL
FLOW IS MORE BACKED THROUGH THE MORNING BEFORE IT STARTS TO VEER
SOME THIS AFTERNOON, THEREFORE WILL NEED TO WATCH FOR SOME
ROTATION IF STRONGER CONVECTIVE ELEMENTS (MORE DISCRETE) CAN
BECOME REALIZED BY EARLY AFTERNOON. AS THE MAIN UPPER-LEVEL
TROUGH ARRIVES DURING THE AFTERNOON AND THE SURFACE COLD FRONT
ALSO STARTS TO APPROACH, STRONG MID TO UPPER LEVEL FLOW WILL
FOSTER GREATER FORCING FOR ASCENT. THIS IS EXPECTED TO RESULT IN
AN INCREASE IN CONVECTIVE DEVELOPMENT, ESPECIALLY TO OUR WEST,
WITH AN INITIAL FOCUS ALONG A PRE- FRONTAL TROUGH. CONVECTION
SHOULD TEND TO ORGANIZE INTO CLUSTERS OR ONE OR MORE LINE
SEGMENTS AS THE LOW- LEVEL FLOW VEERS SOME MORE BY EVENING. THIS
VEERING HOWEVER WILL BE DELAYED THOUGH IF THE WARM FRONT IS
SLOWER TO ADVANCE NORTHWARD, THEREFORE ANY STRONGER CELLS THAT
ESPECIALLY INTERACT WITH THE WARM FRONT WILL NEED TO BE WATCHED
MORE CLOSELY FOR A TORNADO RISK. OTHERWISE, TALL INITIAL CAPE
PROFILES MAY TEND TO WIDEN SOME INTO THIS EVENING AND WITH STEEP
LOW-LEVEL LAPSE RATES THE DCAPE WILL INCREASE. AREAS OF
DAMAGING STRAIGHT-LINE WINDS WILL BE THE MAIN SEVERE WEATHER
HAZARD, WITH THIS POTENTIALLY BECOMING MORE ENHANCED IF
CONVECTION DEVELOPS A COLD POOL WITH BOWING SEGMENTS. SOME MORE
ROBUST CONVECTIVE CORES COULD PRODUCE SEVERE HAIL. THE SEVERE
RISK WILL CONTINUE FOR A TIME THIS EVENING AS INSTABILITY MAY
REMAIN FAVORABLE AS THE UPPER-LEVEL TROUGH AMPLIFIES SOME INTO
THE REGION. CONVECTION MAY TEND TO BECOME MESSY WITH COMPETING
OUTFLOWS WHICH COULD ALSO ENHANCE THE LOCALLY HEAVY RAIN/FLASH
FLOODING RISK.
ANOTHER RISK IS AREAS OF EXCESSIVE RAINFALL THAT COULD LEAD TO FLASH
FLOODING. AS A WARM FRONT LIFTS NORTHWARD, WINDS TURN MORE SOUTHERLY
WITH MOISTURE BEING TRANSPORTED NORTHWARD. PRECIPITABLE WATER VALUES
ARE FORECAST TO SURGE TO 2.00-2.25 INCHES IN THE WAKE OF THE WARM
FRONT. WITHIN THE WARM AIR ADVECTION BURST THROUGH THIS MORNING,
SOME CONVECTION IS ANTICIPATED ESPECIALLY NORTH AND WEST OF I-95.
WHILE THIS ACTIVITY COULD PRODUCE LOCALLY HEAVY RAIN, STORM MOTIONS
SHOULD LIMIT THIS. THE WARM FRONT MAY STALL NEAR THE NJ/NY/PA
BORDER, BUT THIS IS UNCERTAIN. AS ADDITIONAL CONVECTION DEVELOPS
THIS AFTERNOON AND EVENING, DEEPER CONVECTION WILL LIKELY INCREASE
THE RAINFALL RATES WITH THE STRONG CONVECTIVE CORES CAPABLE OF
PRODUCING 1-3 INCHES PER HOUR. SOME AREAS ARE SATURATED, ESPECIALLY
IN NORTHERN NJ AND PORTIONS OF THE PHILADELPHIA METRO, WHICH REMAIN
MORE VULNERABLE TO EXCESSIVE RAINFALL AFTER THIS PAST SEVERAL DAYS.
EXCESSIVE RAINFALL RATES, ESPECIALLY FOR THE URBAN AREAS, COULD LEAD
TO FLASH FLOODING. THIS RISK WILL BECOME ENHANCED WHERE CONVECTION
ENDS UP BEING MORE FOCUSED. THERE WILL BE SOME AREAS THAT COULD GET
2-4 INCHES OF RAIN WHILE SOME AREAS GET MUCH LESS. GIVEN THE
CONTINUED RISK FOR FLASH FLOODING ACROSS THE URBAN CORRIDOR, A FLASH
FLOOD WATCH REMAINS IN EFFECT FOR TODAY THROUGH LATER TONIGHT
(THE MAIN TIME FRAME LOOKS TO BE THIS AFTERNOON AND THIS EVENING).
ON WEDNESDAY, THE COLD FRONT WILL SAG FARTHER SOUTH AND EAST AND
DEPENDING ON HOW QUICKLY THIS CLEARS OUR AREA THERE WILL BE SOME
SHOWERS AND THUNDERSTORMS, ESPECIALLY AS ADDITIONAL SHORTWAVES MOVE
THROUGH THE FLOW WITHIN THE UPPER-LEVEL TROUGH OVERHEAD. THIS LOOKS
TO BE MORE CONCENTRATED ACROSS SOUTHERN NEW JERSEY TO DELMARVA BUT
COULD EXTEND INTO THE I-95 CORRIDOR FOR A TIME. THERE IS SOME SEVERE
WEATHER RISK MAINLY NEAR AND SOUTH/EAST OF THE I-95 CORRIDOR WITH
LOCALLY DAMAGING WIND GUSTS THE MAIN THREAT. THE GREATER INSTABILITY
AND SHEAR LOOKS TO RESIDE ACROSS DELMARVA ON SOUTHWARD, WHERE A
LITTLE HIGHER SEVERE THUNDERSTORM RISK IS INDICATED. SOME LOCALLY
EXCESSIVE RAINFALL IS POSSIBLE WITH SOME LOCAL FLASH FLOOD RISK,
HOWEVER THIS LOOKS TO BE LESS COMPARED TO TODAY GIVEN THE SHIFT
FARTHER SOUTH AND MORE INTO THE COASTAL PLAIN. ONCE THE FRONT MOVES
AWAY BY LATER WEDNESDAY, IT TURNS DRIER FOR THURSDAY/FRIDAY AND
RIGHT INTO THE WEEKEND.
AVIATION /12Z TUESDAY THROUGH SATURDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
TODAY...VFR/MVFR CEILINGS THIS MORNING, POSSIBLY LOCALIZED IFR
CEILINGS FOR A TIME. THE MVFR CEILINGS THEN IMPROVE TO VFR FROM
SOUTH TO NORTH BETWEEN ABOUT 15-18Z. SOME SHOWERS AND A FEW
THUNDERSTORMS THIS MORNING ESPECIALLY NORTH AND WEST OF KPHL,
THEN MORE WIDESPREAD SHOWERS AND THUNDERSTORMS AFTER 18Z FROM
WEST TO EAST WITH MVFR/IFR CONDITIONS AT TIMES. LOCALLY STRONG
WINDS PROBABLE WITH STRONGER THUNDERSTORMS. SOUTHEAST TO SOUTH
WINDS 5-10 KNOTS EARLY THIS MORNING, THEN SOUTH TO SOUTHWEST
WINDS 10-15 KNOTS LATER THIS MORNING AND THIS AFTERNOON WITH
SOME LOCAL GUSTS TO AROUND 20 KNOTS. LOW CONFIDENCE ON SPECIFIC
TIMING DETAILS OF THUNDERSTORMS.
TONIGHT...TIMES OF MVFR/IFR CONDITIONS WITH SHOWERS AND THUNDERSTORMS
IN THE EVENING, THEN MVFR CEILINGS OVERNIGHT AS SHOWERS AND THUNDERSTORMS
TAPER OFF. SOUTH TO SOUTHWEST WINDS 10 KNOTS OR LESS. LOW CONFIDENCE.
OUTLOOK...
WEDNESDAY...SUB-VFR CONDITIONS AT TIMES ALONG WITH SOME SHOWERS
AND THUNDERSTORMS ESPECIALLY NEAR AND SOUTH/EAST OF KPHL.
THURSDAY THROUGH SATURDAY...VFR.
MARINE
SOUTHERLY FLOW INCREASES TODAY, AND SMALL CRAFT ADVISORY CONDITIONS
ARE EXPECTED TO DEVELOP THIS AFTERNOON AND CONTINUE TONIGHT. THE
CONDITIONS DO SUBSIDE THOUGH OVERNIGHT ON DELAWARE BAY. A SMALL
CRAFT ADVISORY REMAINS IN EFFECT STARTING THIS AFTERNOON. GUSTY
THUNDERSTORMS PROBABLE MAINLY LATER THIS AFTERNOON AND THIS EVENING.
OUTLOOK...
WEDNESDAY...SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE OCEAN
ZONES.
THURSDAY THROUGH SATURDAY...THE CONDITIONS ARE ANTICIPATED TO BE
BELOW SMALL CRAFT ADVISORY CRITERIA.
RIP CURRENTS...
FOR TODAY, SOUTHERLY WINDS INCREASE TO 15-25 MPH WITH EITHER A SHORE
PARALLEL OR SLIGHT ONSHORE FLOW EXPECTED DEPENDING ON LOCATION.
BREAKING WAVES OF 2-4 FEET WILL RESULT IN MORE ENERGY WITHIN THE
SURF ZONE. AS A RESULT, MAINTAINED A MODERATE RISK FOR THE
DEVELOPMENT OF DANGEROUS RIP CURRENTS AT ALL BEACHES.
FOR WEDNESDAY, WINDS TURN MORE SOUTHWESTERLY BUT STILL 10-20 MPH.
HOWEVER, BREAKING WAVE HEIGHTS ARE EXPECTED TO INCREASE, WITH
BREAKING WAVES IN THE SURF ZONE AS HIGH AS 5 FEET POSSIBLE. STILL A
7 SECOND PERIOD THOUGH WHICH WILL MITIGATE THE RIP CURRENT THREAT
SOME. HOWEVER, WILL CONTINUE WITH A MODERATE RISK FOR THE
DEVELOPMENT OF DANGEROUS RIP CURRENTS AT ALL BEACHES.
FOR SPECIFIC BEACH FORECASTS, VISIT WEATHER.GOV/BEACH/PHI
PHI WATCHES/WARNINGS/ADVISORIES
PA...FLOOD WATCH THROUGH LATE TONIGHT FOR PAZ070-071-101>106.
NJ...FLOOD WATCH THROUGH LATE TONIGHT FOR NJZ008>010-012>015-
017>019.
DE...FLOOD WATCH THROUGH LATE TONIGHT FOR DEZ001.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM NOON TODAY TO MIDNIGHT EDT TONIGHT
FOR ANZ430-431.
SMALL CRAFT ADVISORY FROM NOON TODAY TO 6 PM EDT WEDNESDAY FOR
ANZ450>455.
DISCUSSION...GORSE
AVIATION...GORSE
MARINE...GORSE/HOEFLICH
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