023
FXUS61 KPHI 091817
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
217 PM EDT SAT MAY 9 2026
WHAT HAS CHANGED
MINOR ADJUSTMENTS TO THE TIMING OF THE STORMS TODAY - HIGHEST
RISK IS NOW THROUGH EARLY THIS EVENING.
THERE IS AN INCREASING RISK FOR PATCHY FOG OVERNIGHT INTO SUNDAY
MORNING.
KEY MESSAGES
1. WIDESPREAD SHOWERS AND A FEW STORMS ARE EXPECTED TODAY. THERE IS
A MARGINAL (1 OUT OF 5) RISK THAT A FEW STORMS COULD BE STRONG
TO SEVERE.
2. FOG IS POSSIBLE ACROSS THE REGION OVERNIGHT INTO SUNDAY
MORNING.
3. SEVERAL OPPORTUNITIES FOR MUCH NEEDED RAINFALL FROM LATE
SUNDAY THROUGH NEXT WEEK.
DISCUSSION
KEY MESSAGE 1...WIDESPREAD SHOWERS AND A FEW STORMS ARE
EXPECTED TODAY. THERE IS A MARGINAL (1 OUT OF 5) RISK THAT A FEW
STORMS COULD BE STRONG TO SEVERE.
THE WEAK AND DIFFUSE WARM FRONT HAS MADE IT THROUGH MUCH OF OUR
REGION AS OF MID DAY SATURDAY. THAT BEING SAID, THE HIGHEST RISK
FOR SEVERE STORMS STILL APPEARS TO BE PRIMARILY OVER THE COASTAL
PLAINS OF SOUTH JERSEY AND DELMARVA THAT SAW SOME CLEARING
EARLIER TODAY AND THUS HAS HAD TEMPERATURES INCREASE AS HIGH AS
THE MID 70S.
AS OF 2 PM, WE ARE STARTING TO SEE SCATTERED SHOWERS DEVELOP.
SO FAR, ONLY ONE STORM HAS HAD ANY LIGHTNING ACTIVITY WITH IT
(IN CENTRAL JERSEY), BUT WITH STILL A FEW MORE HOURS OF DIURNAL
HEATING, WOULD EXPECT SOME MORE SHOWERS TO DEVELOP INTO
THUNDERSTORMS.
INTERESTINGLY, MUCH OF THE SHOWER AND STORM ACTIVITY APPEARS TO
BE INITIATING OFF A WEAK BOUNDARY (I SUSPECT IT IS AN OUTFLOW
BOUNDARY FROM THE MORNING RAIN SHOWERS), THAT LIES TO THE
SOUTHEAST OF THE I-95 CORRIDOR. NORTH AND WEST OF THIS BOUNDARY,
WINDS HAVE SHIFTED IN SOME AREAS OUT OF THE NORTHWEST, WHICH
COULD SLIGHTLY LIMIT THE INSTABILITY IN THESE AREAS.
NO SIGNIFICANT CHANGES IN THE OVERALL NATURE OF THE SEVERE
THREAT. EVEN IN THE COASTAL PLAINS, CAPE VALUES ARE LIKELY TO BE
NEAR OR JUST ABOVE 500 J/KG. SO OVERALL NOT A LOT OF
INSTABILITY. HOWEVER, WINDS ALOFT WILL BE FAIRLY STRONG,
LEADING TO 0-6 KM SHEAR VALUES AROUND 40-45 KT. THE PRIMARY
HAZARD OF CONCERN IS STRONG WINDS, BUT SMALL HAIL IS ALSO
POSSIBLE.
ALL-TOLD, QPF FROM THIS EVENT LOOKS FAIRLY LIGHT, GENERALLY
LESS THAN ONE QUARTER INCH, THOUGH HIGHER AMOUNTS WILL BE
POSSIBLE IN ANY THUNDERSTORMS. SHOWERS AND STORMS LOOK TO EXIT
THE AREA BY LATE EVENING.
KEY MESSAGE 2...FOG IS POSSIBLE ACROSS THE REGION OVERNIGHT
INTO SUNDAY MORNING.
WITH LIGHT WINDS TONIGHT AND SOME RESIDUAL GROUND MOISTURE FROM
RAIN TODAY, THE DEVELOPMENT OF FOG IS LIKELY. MANY OF THE MODEL
SOUNDINGS DEPICT FOG, ESPECIALLY NORTHWEST OF THE I-95 CORRIDOR.
HAVE INCLUDED A MENTION OF PATCHY FOG ACROSS THE AREA.
RIGHT NOW, THE RISK FOR DENSE FOG OR WIDESPREAD FOG IS
RELATIVELY LOW. HOWEVER, IF CLOUDS CLEAR OUT EARLIER THAN
CURRENTLY FORECAST, OR IF WINDS DROP OFF EARLIER, THAT WOULD
INCREASE THE RISK FOR THOSE THREATS.
KEY MESSAGE 3...SEVERAL OPPORTUNITIES FOR MUCH NEEDED RAINFALL
FROM LATE SUNDAY THROUGH NEXT WEEK.
AN UPPER-LEVEL TROUGH IS FORECAST TO DOMINATE ACROSS MUCH OF THE
EAST TO END THIS WEEKEND AND RIGHT THROUGH NEXT WEEK. SOME GUIDANCE
IS MUCH MORE POTENT WITH THE TROUGH AMPLIFICATION LATER NEXT WEEK
WITH A CLOSED LOW DEVELOPING IN THE VICINITY OF THE MID-ATLANTIC.
THESE TROUGHS WILL DRIVE A FEW COLD FRONTS ACROSS OUR AREA, WITH THE
FIRST ONE CROSSING OUR AREA SUNDAY NIGHT INTO MONDAY. THE GREATEST
FORCING WITH THE COLD FRONT LOOKS TO OCCUR FROM THE I-95 CORRIDOR
AND TO THE SOUTH AND EAST SUNDAY AFTERNOON AND ESPECIALLY SUNDAY
NIGHT THROUGH MONDAY MORNING. THIS MAY ALSO OVERLAP FOR A TIME WHEN
SOME SUFFICIENT INSTABILITY IS PRESENT FOR AT LEAST ISOLATED
THUNDERSTORMS. THE FRONT MAY BE SLOW TO SETTLE SOUTH AND EAST LATER
SUNDAY NIGHT INTO MONDAY MORNING AS THE INCOMING MAIN TROUGH AXIS IS
DISPLACED WELL TO OUR NORTHWEST. A MUCH WARMER SUNDAY WILL GIVE WAY
TO A MUCH COOLER MONDAY IN THE WAKE OF THE FRONT.
THE ACTIVE PATTERN LOOKS TO RELOAD AS ANOTHER UPPER-LEVEL TROUGH
QUICKLY REPLACES THE FIRST ONE ACROSS MUCH OF THE EAST. THIS FEATURE
MAY BECOME CLOSED OFF IN THE VICINITY OF THE MID-ATLANTIC WEDNESDAY
THROUGH FRIDAY. THIS INITIAL ARRIVAL OF WARM AIR ADVECTION AHEAD OF
THIS SYSTEM SHOULD DRIVE AN INCREASE IN SHOWER ACTIVITY DURING
WEDNESDAY. THE CHANCE FOR THUNDER IS LESS CERTAIN AT THIS TIME FRAME
AS IT WILL DEPEND ON HOW MUCH DESTABILIZATION CAN OCCUR. IF THE
SYSTEM CLOSES OFF AS IT ARRIVES THURSDAY INTO FRIDAY, THEN SURFACE
LOW PRESSURE MAY END UP DEVELOPING OFF THE NORTHERN MID-ATLANTIC
COAST. THIS WOULD INCREASE THE INTENSITY AND COVERAGE OF
SHOWERS/RAIN AND RESULT IN A STRONGER ONSHORE FLOW AND THEREFORE
EVEN COOLER TEMPERATURES. THIS WOULD ALSO TEND TO RESULT IN A MORE
STABLE AIR MASS AND THUS LITTLE TO NO RISK OF THUNDER. THE UPPER AIR
PATTERN EVOLVING DURING THE SECOND HALF OF NEXT WEEK IS LESS
CERTAIN, AS THE AMOUNT AND COVERAGE OF PRECIPITATION WILL DEPEND ON
WHETHER WE END UP WITH A CLOSED LOW OR JUST A SHARPER UPPER-LEVEL
TROUGH THAT QUICKLY PIVOTS THROUGH.
AVIATION /18Z SATURDAY THROUGH THURSDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS...
THROUGH 00Z...PREVAILING VFR. ISOLATED TSRA IS POSSIBLE. THE
HIGHEST RISK FOR TSRA DIRECTLY AFFECTING A TAF SITE IS AT KMIV
AND KACY. FOR KPHL, KPNE, KTTN, AND KILG, THERE IS A RISK FOR
TSRA IN THE VICINITY, PRIMARILY TO THE SOUTH AND EAST, BUT THE
RISK DIRECTLY OVER THE TAF SITE IS RELATIVELY LOW. MVFR OR
LOWER VISIBILITIES ARE POSSIBLE IN ANY HEAVIER SHOWERS OR
STORMS. SOUTH-SOUTHWEST WINDS 10-15 KT, WITH SOME GUSTS AROUND
20 KT. MODERATE CONFIDENCE.
TONIGHT...STORMS SHOULD CLEAR OUT BY OR JUST AFTER 00Z, LEAVING
VFR CONDITIONS TO START THE OVERNIGHT PERIOD. THERE IS AN
INCREASING RISK FOR FOG OVERNIGHT, PARTICULARLY AFTER 06Z.
THERE IS SOME RISK ACROSS THE REGION, BUT THE HIGHEST RISK FOR
IFR AND EVEN LIFR CONDITIONS IS AT KRDG AND KABE AT THIS POINT.
WINDS QUICKLY DIMINISHING TO LIGHT AND VARIABLE BY 01-03Z WITH
CALM PERIODS LIKELY OVERNIGHT. MODERATE CONFIDENCE OVERALL, LOW
CONFIDENCE IN THE EXTENT OF RESTRICTIONS FROM LOW STRATUS OR
FOG.
SUNDAY...ONCE ANY MORNING FOG CLEARS OUT BY 15Z, PREVAILING VFR
CONDITIONS LIKELY. 20 TO 40% CHANCE FOR SHRA AND TSRA AFTER
18Z. IF ANY SHRA OR TSRA MOVE OVER A TAF SITE, CEILINGS AND
VISIBILITIES COULD BRIEFLY DROP TO MVFR. WINDS OUT OF THE WEST
NEAR OR BELOW 10KT THROUGH MUCH OF THE DAY. MODERATE CONFIDENCE
IN THE OVERALL PATTERN, LOW CONFIDENCE IN ANY ONE TAF SITE BEING
DIRECTLY AFFECTED BY SHRA OR TSRA.
OUTLOOK...
SUNDAY NIGHT AND MONDAY...A PERIOD OF SUB-VFR CONDITIONS
PROBABLE LATER SUNDAY AFTERNOON INTO MONDAY MORNING WITH
SHOWERS. A FEW THUNDERSTORMS POSSIBLE SUNDAY AFTERNOON INTO
EARLY SUNDAY EVENING. CONDITIONS SHOULD IMPROVE DURING MONDAY.
TUESDAY...VFR.
WEDNESDAY...SUB-VFR CONDITIONS POSSIBLE ALONG WITH SHOWERS.
MARINE
A SMALL CRAFT ADVISORY IS REMAINS IN EFFECT FOR ALL NJ AND DE
ATLANTIC COASTAL WATERS AND THE LOWER DELAWARE BAY AND CONTINUE
THROUGH 12 AM SUNDAY. SOUTH WINDS 15-20 KT WITH GUSTS AROUND 25
KT ARE EXPECTED THROUGH THIS EVENING. SEAS ARE EXPECTED TO BE
3-5 FEET. IN ADDITION, SHOWERS AND A FEW STORMS COULD CONTRIBUTE
TO HAZARDOUS MARINE CONDITIONS. OVERNIGHT, WINDS AND SEAS ARE
EXPECTED TO SUBSIDE BELOW SCA LEVELS AND CONTINUE THROUGH THE
DAY ON SUNDAY.
OUTLOOK...
MONDAY...A BRIEF PERIOD OF SMALL CRAFT ADVISORY CONDITIONS
POSSIBLE.
TUESDAY...THE CONDITIONS ARE ANTICIPATED TO BE BELOW SMALL CRAFT
ADVISORY CRITERIA.
WEDNESDAY...A PERIOD OF SMALL CRAFT ADVISORY CONDITIONS
POSSIBLE.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ431-
450>455.
DISCUSSION...COOPER/GORSE/JOHNSON
AVIATION...COOPER/GORSE/JOHNSON
MARINE...COOPER/GORSE/JOHNSON
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