505
FXUS61 KPHI 012024
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
424 PM EDT TUE SEP 1 2026
WHAT HAS CHANGED
INCREASED CONFIDENCE IN THE TIMING OF STORMS LATER TODAY.
FOR WEDNESDAY, MODELS TRENDING SLIGHTLY COLDER FOR MUCH OF THE
REGION, LIMITING THE INSTABILITY WITH STORM CHANCES.
THE CHANCE FOR SHOWERS AND THUNDERSTORMS SHIFTED A BIT NORTH ON
FRIDAY. FRIDAY AFTERNOON HIGH TEMPERATURES ALSO INCHED UP A FEW
DEGREES.
KEY MESSAGES
1. SCATTERED SEVERE THUNDERSTORMS ARE FORECAST TO DEVELOP LATE THIS
AFTERNOON AND EVENING ACROSS PORTIONS OF NEW JERSEY AND EASTERN
PENNSYLVANIA. DAMAGING WIND GUSTS, LARGE HAIL, AND A TORNADO OR TWO
WILL BE POSSIBLE.
2. ON WEDNESDAY, A SHORTWAVE TROUGH COULD SPARK ANOTHER ROUND OF
SHOWERS AND STORMS, BUT IT WILL BE WORKING AGAINST A RELATIVELY
STABLE BOUNDARY LAYER.
3. HOT AND HUMID CONDITIONS ARE FORECAST ACROSS THE REGION ON
THURSDAY.
4. UNSETTLED CONDITIONS WILL CONTINUE ON THURSDAY WITH THE POTENTIAL
FOR SEVERE THUNDERSTORMS. SCATTERED THUNDERSTORMS ARE AGAIN POSSIBLE
ON FRIDAY, MAINLY FROM PHILADELPHIA SOUTH.
5. THE LABOR DAY WEEKEND WILL FEATURE MOSTLY DRY WEATHER WITH AT OR
BELOW NORMAL TEMPERATURES AND LOWER HUMIDITY.
DISCUSSION
KEY MESSAGE 1...SCATTERED SEVERE THUNDERSTORMS ARE FORECAST TO
DEVELOP LATE THIS AFTERNOON AND EVENING ACROSS PORTIONS OF NEW
JERSEY AND EASTERN PENNSYLVANIA. DAMAGING WIND GUSTS, LARGE HAIL,
AND A TORNADO OR TWO WILL BE POSSIBLE.
THE NOW STATIONARY FRONT IS NORTH OF OUR REGION NOW. AN APPROACHING
MID LEVEL TROUGH IS EXPECTED TO RESULT IN SHOWERS AND STORMS
DEVELOPING ALONG THE FRONT AND THEN PROGRESSING SOUTHWARD THROUGH
THE EVENING. THE MAIN TIMING FOR THIS ROUND OF SHOWERS AND STORMS
APPEARS TO BE FROM 6 PM THROUGH MIDNIGHT. AS FAR AS THE HAZARDS WITH
THE STORMS, IT STILL APPEARS THAT THE PRIMARY HAZARDS ARE DAMAGING
WINDS AND CLOUD-TO-GROUND LIGHTNING, BUT THERE IS POTENTIAL ALSO FOR
LARGE HAIL, HEAVY RAIN, AND TORNADOES.
SURFACE BASED CAPE VALUES ABOVE 2000 J/KG WILL BE POSSIBLE AS THE
STORMS APPROACH, THANKS IN PART TO THE BREAKS IN THE CLOUDS THAT WE
HAVE SEEN SINCE THE EARLIER LINE OF SHOWERS MOVED SOUTH OF THE
REGION. EFFECTIVE SHEAR STILL LOOKS LIKE IT WILL BE IN THE 30 - 40
KT RANGE, EVEN WELL SOUTH OF THE FRONT. HOWEVER, AS MENTIONED BY THE
PREVIOUS SHIFT, LOW LEVEL SHEAR IS LIMITED FOR MOST OF THE REGION,
BUT DIRECTIONAL SHEAR IS SUFFICIENT FOR AT LEAST SOME TORNADO RISK,
PARTICULARLY FOR CENTRAL AND NORTHERN JERSEY. ALL THAT TO SAY,
DAMAGING WINDS STILL APPEAR TO BE THE PRIMARY THREAT, WITH LARGE
HAIL AND TORNADOES LESS LIKELY, BUT STILL A THREAT.
STORM MOTIONS LOOK TO BE FAST ENOUGH TO LIMIT THE FLOODING THREAT,
AND THERE DOESN'T APPEAR MUCH RISK FOR TRAINING STORMS. IF THERE IS
HEAVY ENOUGH RAIN IN A SHORT AMOUNT OF TIME, THERE COULD BE SOME
ISSUES WITH THE MORE FLASH FLOOD VULNERABLE AREAS, SUCH AS HIGHLY
URBANIZED AREAS, BUT THAT THREAT IS LIMITED.
AS FOR THE HEAT ADVISORY, HEAT INDEX VALUES IN THE URBAN CORRIDOR
ARE FLIRTING WITH 100 DEGREES, SO WILL KEEP THE ADVISORY GOING AS
IS.
KEY MESSAGE 2...ON WEDNESDAY, A SHORTWAVE TROUGH COULD SPARK ANOTHER
ROUND OF SHOWERS AND STORMS, BUT IT WILL BE WORKING AGAINST A
RELATIVELY STABLE BOUNDARY LAYER.
IN THE WAKE OF THE STORMS TUESDAY NIGHT, THE FRONT IS EXPECTED TO
SINK BACK SOUTH OF THE REGION BY WEDNESDAY MORNING, LEAVING OUR
REGION IN THE RELATIVELY COOLER AND MORE STABLE AIR MASS NORTH OF
THE FRONT. THE NET RESULT IS THAT OUR REGION SHOULD BE IN
NORTHEASTERLY FLOW, AND RELATIVELY CLOUDY CONDITIONS FOR MUCH OF THE
DAY. AS A RESULT, SURFACE-BASED INSTABILITY IS GOING TO BE ALMOST
NON-EXISTENT, THOUGH MODEL SOUNDINGS DO SHOW ELEVATED INSTABILITY
FOR PARCELS ABOVE 900 MB.
CONSEQUENTLY, THE RISK FOR SEVERE STORMS IS STILL QUITE CONDITIONAL
AND UNCERTAIN. GIVEN HOW SHARP OF A MID LEVEL SHORT WAVE TROUGH IS
APPROACHING, THERE WILL BE AMPLE FORCING, BUT IT IS A QUESTION OF IF
THE ELEVATED INSTABILITY WILL BE ENOUGH TO SUSTAIN STORMS IN OUR
REGION.
KEY MESSAGE 3...HOT AND HUMID CONDITIONS ARE FORECAST ACROSS THE
REGION ON THURSDAY.
AFTER A COOL DOWN ON WEDNESDAY FOR MOST NEIGHBORHOODS (5 TO 10
DEGREES LOWER - LESS ACROSS DELMARVA), HOT AND HUMID CONDITIONS ARE
ONCE AGAIN EXPECTED ACROSS THE REGION ON THURSDAY AS THE FRONTAL
BOUNDARY LIFTS NORTH. WITH THE FRONT TO THE NORTH, HIGH TEMPERATURES
ARE FORECAST TO CLIMB INTO THE UPPER 80S TO MID 90S FOR MANY AREAS
(AROUND 80 OR LOW 80S FAR N AND W). THESE TEMPERATURES COMBINED WITH
DEWPOINTS IN THE LOW TO MID 70S WILL AGAIN RESULT IN HEAT INDICES
WELL INTO THE 90S TO LOW 100S SOUTH OF I-78, PERHAPS EVEN AS HIGH AS
105 DEGREES FOR DELMARVA.
ANOTHER HEAT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE AREA ON
THURSDAY IF THIS TREND CONTINUES.
KEY MESSAGE 4...UNSETTLED CONDITIONS WILL CONTINUE ON THURSDAY WITH
THE POTENTIAL FOR SEVERE THUNDERSTORMS. SCATTERED THUNDERSTORMS ARE
AGAIN POSSIBLE ON FRIDAY, MAINLY FROM PHILADELPHIA SOUTH.
ANOTHER ROUND OF SEVERE THUNDERSTORMS ARE POSSIBLE ON THURSDAY.
FRIDAY COULD ALSO EXPERIENCE A FEW SEVERE STORMS ACROSS DELMARVA,
DEPENDING ON HOW QUICKLY THE FRONTAL BOUNDARY PUSHES SOUTH.
SPC HAS A SLIGHT RISK (LEVEL 2 OUT OF 5) FOR SEVERE THUNDERSTORMS
ON THURSDAY FROM ABOUT WILMINGTON TO WILDWOOD NJ SOUTHWARD AND A
MARGINAL RISK (LEVEL 1) TO THE NORTH OF THIS.
THE NORTHWEST FLOW PATTERN WILL REMAIN IN PLACE ON THURSDAY AND WILL
CONTINUE TO BE SUPPORTIVE OF ALL SEVERE THREATS, INCLUDING DAMAGING
WINDS, LARGE HAIL, AND A FEW TORNADOES, DEPENDING ON HOW ALL THE
MESOSCALE DETAILS PAN OUT. THE THREAT FOR FLASH FLOODING IS
TYPICALLY LOWER WITH THESE PATTERNS, BUT NOT ZERO. TRAINING CAN
STILL OCCUR AND A SINGLE LOCALE COULD HAVE MULTIPLE DAYS WITH HEAVY
RAINFALL.
FRIDAY'S SPC'S 15% PROBABILITIES FOR SEVERE THUNDERSTORMS HAVE
SHIFTED JUST SOUTH OF OUR DELMARVA ZONES, THOUGH THERE IS STILL SOME
UNCERTAINTY WITH THIS. OUR LATEST FORECAST HAS ABOUT A 30-40% CHANCE
OF SHOWERS AND THUNDERSTORMS SOUTH OF ABOUT PHILADELPHIA.
KEY MESSAGE 5...THE LABOR DAY WEEKEND WILL FEATURE MOSTLY DRY
WEATHER WITH AT OR BELOW NORMAL TEMPERATURES AND LOWER HUMIDITY.
BY SATURDAY, CURRENT MODEL CONSENSUS INDICATES THE FRONTAL BOUNDARY
WILL BE PUSHING SOUTH OF OUR REGION WITH CANADIAN HIGH PRESSURE
BUILDING ACROSS THE NORTHEAST AND MID-ATLANTIC. THIS WILL LARGELY
END ANY SHOWER AND THUNDERSTORM POTENTIAL. THUS, LABOR DAY WEEKEND
IS STILL SHAPING UP TO FEATURE NICE WEATHER, WITH TEMPERATURES
TRENDING AT OR SLIGHTLY BELOW NORMAL AND LOWER HUMIDITY. THE ONLY
ROAD BUMP AT THE MOMENT, COULD BE A COLD FRONT THAT APPROACHES THE
FORECAST AREA VERY LATE ON MONDAY.
AVIATION /20Z TUESDAY THROUGH SUNDAY/
THROUGH TONIGHT...EXPECT A BROKEN LINE OF STORMS TO MOVE FROM NORTH
TO SOUTH ACROSS THE TAF SITES BETWEEN 22 AND 04Z. AHEAD OF THIS
LINE, EXPECT VFR CONDITIONS. WITH AND BEHIND THIS LINE, EXPECT MVFR
CONDITIONS, ESPECIALLY WITH MVFR CEILINGS BEHIND THE LINE, TO
DEVELOP. WINDS SHOULD BE MOSTLY OUT OF THE SW AHEAD OF THE STORMS.
WITH AND BEHIND THE LINE OF STORMS, EXPECT AN ABRUPT SHIFT TO
NORTHEASTERLY WINDS, BUT WIND SPEEDS (OUTSIDE OF THE VICINITY OF ANY
THUNDERSTORMS) SHOULD STAY NEAR OR BELOW 10 KT.
WEDNESDAY...PREVAILING VFR. THERE IS A 20 TO 40% CHANCE FOR SHOWERS
AND STORMS THROUGH THE DAY TIME THAT COULD RESULT IN TEMPORARY MVFR
OR LOWER CONDITIONS, HOWEVER, THERE IS CONSIDERABLE UNCERTAINTY TO
THE EXTENT OF STORM DEVELOPMENT TOMORROW. WINDS PRIMARILY OUT OF THE
NORTHEAST AND EAST AROUND 10 KT THROUGH THE DAY.
OUTLOOK...
THURSDAY AND FRIDAY...SUB-VFR CONDITIONS ARE POSSIBLE IN SHOWERS AND
THUNDERSTORMS EACH DAY (20-40% CHANCE), MAINLY DURING THE AFTERNOON
TO EVENING HOURS.
SATURDAY AND SUNDAY...PRIMARILY VFR CONDITIONS EXPECTED.
MARINE
WINDS AND SEAS ARE EXPECTED TO STAY BELOW SMALL CRAFT ADVISORY
CONDITIONS. HOWEVER, GUSTY AND ERRATIC WINDS ARE POSSIBLE IN THE
VICINITY OF ANY STORMS, PARTICULARLY TONIGHT.
OUTLOOK...
THURSDAY THROUGH SUNDAY...SUB-SCA CONDITIONS ARE EXPECTED THROUGH
THE PERIOD. THERE IS A CHANCE (40 TO 50%) FOR THUNDERSTORMS
THURSDAY, MAINLY IN THE AFTERNOON AND EVENING HOURS. FOR FRIDAY, THE
CHANCE OF THUNDERSTORMS (30 TO 40%) SHIFTS SOUTH A BIT, BASICALLY
EXTENDING FROM MANASQUAN INLET, NJ DOWN TO FENWICK ISLAND, DE.
RIP CURRENTS...
ON WEDNESDAY, NORTHEAST FLOW WILL RANGE FROM 10 TO 15 MPH WITH
GUSTS UP TO 20 MPH ALONG THE NEW JERSEY COAST. THERE WILL BE
SOUTHEAST SWELLS WITH A PERIOD AROUND 10 SECONDS AND BREAKING
WAVES OF 2 TO 3 FEET. AS A RESULT, THERE IS A MODERATE RISK FOR
THE DEVELOPMENT OF DANGEROUS AND LIFE THREATENING RIP CURRENTS
FOR THE JERSEY SHORE ALONG MONMOUTH, OCEAN, AND ATLANTIC
COUNTIES, AND A LOW RISK FOR THE DEVELOPMENT OF DANGEROUS AND
LIFE THREATENING RIP CURRENTS FOR THE JERSEY SHORE IN CAPE MAY
COUNTY AND DELAWARE BEACHES.
FOR THURSDAY, WINDS BECOME SOUTHWEST AT 10 TO 15 MPH WITH GUSTS
UP TO 20 MPH ALONG THE JERSEY SHORE. BREAKING WAVES WILL RANGE
FROM 1 TO 3 FEET WITH LIGHT EASTERLY SWELLS WITH A PERIOD AROUND
6 SECONDS. AS A RESULT, THERE IS A MODERATE RISK FOR THE
DEVELOPMENT OF DANGEROUS AND LIFE THREATENING RIP CURRENTS FOR
THE JERSEY SHORE ALONG MONMOUTH, OCEAN, AND ATLANTIC COUNTIES,
AND A LOW RISK FOR THE DEVELOPMENT OF DANGEROUS AND LIFE
THREATENING RIP CURRENTS FOR THE JERSEY SHORE IN CAPE MAY COUNTY
AND DELAWARE BEACHES.
PHI WATCHES/WARNINGS/ADVISORIES
PA...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR PAZ070-071-102-
104-106.
NJ...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR NJZ015-017>019.
DE...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR DEZ001.
MD...NONE.
MARINE...NONE.
DISCUSSION...
AVIATION...WFO PHI
MARINE...MPS
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