Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 290115
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
915 PM EDT TUE JUL 28 2015

.SYNOPSIS...
HIGH PRESSURE WILL SLIDE OFF THE COAST ON WEDNESDAY GIVING WAY TO A
WEAK COLD FRONT PASSAGE ON THURSDAY INTO FRIDAY MORNING. ANOTHER
WEAK FRONT MAY CROSS THE REGION SUNDAY INTO MONDAY FOLLOWED BY A
BRIEF SHOT OF HIGH PRESSURE. AFTER THE RESPITE OF HIGH PRESSURE A
STRONGER COLD FRONT IS EXPECTED TO PASS THROUGH ON TUESDAY.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
00Z SURFACE ANALYSIS SHOWS A QUASI-STATIONARY BOUNDARY ALONG THE
MASON-DIXON LINE, STRETCHING NORTHEASTWARD ACROSS SOUTHEAST PA AND
CENTRAL NJ. THE BOUNDARY WAS NOTED BY A SHARP DEWPOINT GRADIENT WITH
DEWPOINTS NEAR 60F TO THE NORTH AND LOW 70S TO THE SOUTH. THE LATEST
SPC MESOANALYSIS REVEALS A SIMILAR TIGHT GRADIENT IN MLCAPE WITH
VALUES RANGING FROM AOB 500 J/KG NORTH OF THE BOUNDARY TO 2000
J/KG FARTHER SOUTH. SHOWERS AND STORMS WERE CONFINED TO THE
SOUTHEASTERN HALF OF THE CWA WHERE THE HIGHER INSTABILITY RESIDES.
WITH A LACK OF ORGANIZED LIFT OVER THE REGION AND DISSIPATING
SEABREEZES, CONVECTION HAS FOLLOWED THE DIURNAL TREND AND IS
WANING QUICKLY THIS EVENING AS THE ATMOSPHERE STABILIZES. ASIDE
FROM A COUPLE OF LEFTOVER SHOWERS POSSIBLE IN PHILLY, SOUTHERN NJ
AND THE DELMARVA THIS EVENING, TONIGHT WILL BE DRY.

THE BOUNDARY IS EXPECTED TO STALL AND BASICALLY WASH OUT OVER THE
AREA TONIGHT. OVERNIGHT FOG DEVELOPMENT WOULD BE FAVORED IN THE
MOIST AIRMASS SOUTH OF THIS BOUNDARY, ESPECIALLY FOR THE FEW LOCALES
THAT RECEIVED RAIN TODAY.

MINIMUM TEMPERATURES ARE ANTICIPATED TO BE MAINLY IN THE UPPER 60S
AND LOWER 70S WITH A LIGHT SOUTHWEST TO SOUTH SURFACE FLOW.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
THE AXIS OF THE MID LEVEL RIDGE IS FORECAST TO DRIFT EASTWARD AND IT
SHOULD APPROACH OUR REGION LATE ON WEDNESDAY. AS A RESULT, THE
POTENTIAL FOR SHOWERS AND THUNDERSTORMS WILL BE EVEN LOWER THAN IT
WAS TODAY. WE ARE EXPECTING A MOSTLY SUNNY SKY FOR WEDNESDAY WITH
SOME CIRRUS OVERHEAD ALONG WITH THE DEVELOPMENT OF SCATTERED CUMULUS.

MAXIMUM TEMPERATURES ARE FORECAST TO RANGE FROM 90 TO 95 IN MUCH OF
OUR REGION. READINGS SHOULD GET NO HIGHER THAN THE MIDDLE AND UPPER
80S IN THE ELEVATED TERRAIN UP NORTH AND ALONG THE IMMEDIATE COAST.

IT APPEARS AS THOUGH SLIGHTLY DRIER AIR WILL MIX TO THE SURFACE FROM
ALOFT FOR WEDNESDAY AFTERNOON. DEW POINT READINGS ARE EXPECTED TO
FAVOR THE MIDDLE 60S ON WEDNESDAY AFTERNOON, EXCEPT IN DELAWARE AND
NORTHEASTERN MARYLAND WHERE THE BAYS SHOULD HELP KEEP DEW POINT
READINGS IN THE UPPER 60S AND LOWER 70S.

THE COMBINATION OF TEMPERATURE AND DEW POINT IS ANTICIPATED TO RESULT
IN MAXIMUM HEAT INDEX VALUES BEING NEAR OR A DEGREE OR TWO ABOVE THE
MAXIMUM AIR TEMPERATURES IN EASTERN PENNSYLVANIA AND NEW JERSEY. THE
IMPACT OF THE HIGHER HUMIDITY ON THE DELMARVA SHOULD BRING MAXIMUM
HEAT INDEX VALUES SOLIDLY INTO THE UPPER 90S THERE WITH PERHAPS A
FEW SPOTS HITTING 100, ESPECIALLY SOUTH OF THE CANAL.

WE WILL NOT BE ISSUING A HEAT ADVISORY OR AN EXCESSIVE HEAT WARNING
AT THIS TIME SINCE ALL LOCATIONS IN OUR FORECAST AREA ARE EXPECTED
TO REMAIN JUST BELOW THE ISSUANCE CRITERIA.

A SOUTHWEST TO SOUTH WIND AROUND 5 TO 10 MPH IS EXPECTED FOR
WEDNESDAY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
5-WAVE MODEL GUIDANCE SHOWS SOUTHEAST RIDGING GIVING WAY TO A
DEVELOPING TROUGH ACROSS THE NORTHEASTERN HALF OF THE CONUS BY THE
WEEKEND. A FEW IMPULSES WILL TRAVERSE THROUGH THE BASE OF THE TROUGH
NEXT WEEK PROVIDING CHANCES FOR MORE UNSETTLED WEATHER EARLY NEXT
WEEK.

THURSDAY...INCREASING MOISTURE FLUX AHEAD OF THE WEAKENING COLD
FRONT MAY BRING IN MORE CLOUD COVER THAN PREVIOUSLY EXPECTED. THERE
COULD BE ENOUGH INSTABILITY ADVECTING IN ALOFT TO SPARK SCATTERED
SHOWERS WITH EMBEDDED THUNDER DURING THE MORNING HOURS, MOSTLY
ACROSS THE SOUTH AND WEST, TO KEEP TEMPERATURES FROM REALLY PEAKING
AS HIGH AS PREVIOUSLY THOUGHT, THOUGH LOW-90S IS NOTHING TO SNEEZE
AT. THERE WILL BE SOME ENHANCED VERTICAL MIXING DURING THE AFTERNOON
WHICH SHOULD KEEP DEWPOINTS FROM STAYING IN THE LOW-70S, SO
EXPECTING THEM TO MIX OUT INTO THE UPPER-60S...SHOULD KEEP HEAT
INDEX VALUES JUST BELOW ADVISORY CRITERIA BUT STILL HAVE SOME TIME
FOR FURTHER ASSESSMENT. BESIDES THE HEAT, THE APPROACH OF THE COLD
FRONT LATER IN THE AFTERNOON, WILL TRIGGER MORE SCATTERED SHOWERS
AND THUNDERSTORMS. INSTABILITY IS PREVALENT BUT SHEAR IS ON THE
WEAKER SIDE AS OF NOW BUT DEPENDING ON THE SHEAR AXIS ORIENTATION
TO THE STORMS, WE COULD SEE CELL MERGER OCCUR FORMING A BROKEN
LINE OF STORMS WITH STRONGER WINDS THE MAIN ISSUE. PWATS APPROACH
AND COULD SURPASS 2" SO HEAVY EFFICIENT RAINERS IS ALSO LIKELY
WITH POOR DRAINAGE AND SPOTTY FLASH FLOOD ISSUES POSSIBLE.

FRIDAY - SUNDAY...AS MID-LEVEL TROUGHING BEGINS TO STRENGTHEN BY THE
WEEKEND, THE AFOREMENTIONED FRONT BECOMES MORE PARALLEL TO THE UPPER-
LEVEL FLOW...IT LOOKS TO STALL OFFSHORE. IT BEGINS TO SLOW ITS
DEPARTURE EARLY ON FRIDAY SO THERE COULD BE SOME LINGERING SHOWERS
AND THUNDERSTORMS FRIDAY MORNING BEFORE DRYING OUT. TEMPERATURES
WILL STILL BE QUITE WARM BUT THE FRONT SHOULD BE ABLE TO EAT UP THE
HIGHER DEWPOINTS AS THE AIRMASS DRIES OUT A BIT. WE LOOK TO BE ON
THE SOUTHERN EXTENT OF THE TROUGHING SO MOST OF THE MID-LEVEL ENERGY
STAYS TO OUR NORTH THROUGH THE WEEKEND KEEPING US MOSTLY DRY...COULD
BE SOME ISOLATED SHOWERS ACROSS SOUTHERN DELMARVA CLOSER TO THE
STALLED BOUNDARY. TEMPERATURES ON SATURDAY AND SUNDAY WILL STILL
REMAIN 90+ DEGREES.

MONDAY -  TUESDAY...ANOTHER COLD FRONT IS PROGGED TO PUSH CLOSER TO
THE REGION BY LATE MONDAY INTO TUESDAY. TEMPERATURES AHEAD OF THE
FRONT WILL ONCE AGAIN BE 90+ DEGREES WITH A MOISTENING AIRMASS.
MORE SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

SHOWERS AND STORMS HAVE DISSIPATED AFTER SUNSET. EXPECT A PERIOD
OF VFR THIS EVENING BEFORE FOG DEVELOPS OVERNIGHT. THE BEST FOG
POTENTIAL APPEARS TO BE AT ILG/MIV/ACY WHERE HIGHER DEWPOINTS
RESIDE. ACY MAY BE PARTICULARLY SUSCEPTIBLE TO FOG/LOW CLOUDS
TONIGHT AS THE GROUND IS WET FROM EARLIER RAINFALL. A PERIOD OF
MVFR VSBYS AND/OR CIGS LIKELY WITH IFR POSSIBLE BETWEEN ABOUT
06-12Z. CONFIDENCE IN FOG LOWERS FARTHER NORTH AND WEST TOWARD
RDG AND ABE AS THEY CURRENTLY RESIDE ON THE DRIER SIDE OF THE
BOUNDARY, BUT THE BOUNDARY MAY TRY TO DRIFT NORTHWARD.

VFR CONDITIONS WITH SCATTERED CUMULUS IS IN THE FORECAST FOR
WEDNESDAY. THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS IS VERY LOW.

A LIGHT/VARIABLE WIND TONIGHT AND WEDNESDAY MORNING, BECOMING
S-SW 5-10 KT BY THE AFTERNOON.

OUTLOOK...
THURSDAY...EARLY MORNING FOG/HAZE WITH MVFR CONDITIONS POSSIBLE...THEN
SCT AFTERNOON/EVENING TSTMS WITH MVFR OR LOWER CONDS.

FRIDAY - SUNDAY...VFR.

&&

.MARINE...
WEAK HIGH PRESSURE WILL CONTINUE TO AFFECT THE COASTAL WATERS OF NEW
JERSEY AND DELAWARE FOR TONIGHT AND WEDNESDAY.

A SOUTHWEST TO SOUTH WIND AROUND 5 TO 10 KNOTS IS EXPECTED. WAVE
HEIGHTS ON THE OCEAN WILL FAVOR 2 TO 3 FEET WHILE WAVES ON DELAWARE
BAY SHOULD BE 2 FEET OR LESS.

OUTLOOK...
THURSDAY - SUNDAY...SUB-SCA CONDITIONS EXPECTED THIS PERIOD.
THUNDERSTORM CHANCES INCREASE ON THURSDAY WITH VERY HEAVY RAINFALL
AND STRONG WIND GUSTS POSSIBLE.

&&

.RIP CURRENTS...
THERE IS A MODERATE RISK FOR THE DEVELOPMENT OF DANGEROUS RIP
CURRENTS ALONG THE NEW JERSEY AND DELAWARE COAST ON WEDNESDAY DUE
TO A LONG PERIOD SOUTHEASTERLY SWELL. THE WAVE PERIOD WILL
CONTINUE TO BE AROUND 10 SECONDS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...HEAVENER
NEAR TERM...KLEIN
SHORT TERM...IOVINO
LONG TERM...HEAVENER
AVIATION...IOVINO/HEAVENER/KLEIN
MARINE...IOVINO/HEAVENER
RIP CURRENTS...IOVINO/KLEIN


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