Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 140141
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
941 PM EDT SUN APR 13 2014

.SYNOPSIS...
HIGH PRESSURE CONTINUES TO SLIDE EAST OFF THE SHORE TONIGHT. A COLD
FRONT WILL APPROACH FROM THE WEST TOMORROW NIGHT AND PUSH THROUGH
THE REGION TUESDAY AFTERNOON. IN THE WAKE OF THE COLD FRONT, HIGH
PRESSURE WILL SETTLE IN OVER THE REGION THROUGH THE REMAINDER OF THE
WORK WEEK. AN UPPER LEVEL TROUGH COULD SLIDE OVER OUR REGION EARLY
NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
WIND GUSTS HAVE DIMINISHED FOR MOST SITES NOW THAT DAYTIME MIXING
HAS SUBSIDED AFTER THE SUN HAS SET. ANY PLACES THAT REMAIN GUSTY
EARLY THIS EVENING, EVEN CLOSER TO THE COAST WHERE WINDS ARE THE
STRONGEST, SHOULD LOSE THEIR GUSTINESS WITHIN THE NEXT HOUR OR
TWO. SOME ADJUSTMENTS HAVE BEEN MADE TO THE HOURLY GRIDS, BUT
OVERNIGHT LOW TEMPERATURE FORECAST WAS NOT CHANGED. AN INCREASE IN
CLOUD COVER OVERNIGHT, THE EXPECTATION THAT SOME WINDS WILL REMAIN
OVERNIGHT, AND THE FACT THAT DEWPOINTS REMAIN RELATIVELY HIGH
SHOULD KEEP TEMPERATURES FROM DROPPING SIGNIFICANTLY OVERNIGHT. IF
MORE SIGNIFICANT BREAKS IN THE MID-HIGH LEVEL CLOUD COVER OCCUR,
AND WINDS BECOME LIGHTER THAN EXPECTED, TEMPERATURES COULD DROP
MORE THAN CURRENTLY FORECAST.

STILL UNSURE HOW MUCH STRATUS AND/OR FOG FORMS LATE TONIGHT ACROSS
THE REGION. DEWPOINTS ARE MUCH HIGHER THAN THEY WERE LAST BUT THE
BOUNDARY LAYER WINDS WERE ALSO MUCH WEAKER LAST NIGHT ALLOWING
BETTER MOISTURE POOLING TO OCCUR. STILL, GUIDANCE CONTINUES TO
INDICATE THE POTENTIAL FOR MOSTLY STRATUS TO FORM OVERNIGHT
TOWARD DAYBREAK MONDAY NEAR THE TOP OF THE INVERSION, SO WE WILL
INCREASE CLOUD COVER OVERNIGHT.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
ANY LOWER CLOUDS AND FOG SHOULD BURN OFF LATE MORNING GIVING WAY TO
THE MID AND HIGHER LEVEL CLOUDS. THE RIDGING OFFSHORE SHOULD
CONTINUE TO PUSH EASTWARD AND SOME LOWER HEIGHTS AND THICKNESSES
ADVECT INTO THE REGION FROM THE WEST. THE GRADIENT FLOW WILL STILL
BE FROM THE SOUTH-SOUTHWEST WHERE THE GUIDANCE IS SHOWING SLIGHTLY
COOLER LOW-LEVEL TEMPERATURES. ALL INDICATIONS SHOW MONDAY BEING A
COUPLE DEGREES COOLER THAN SUNDAY WITH THE NEUTRAL/COOLER AIR
ADVECTION OCCURRING AND MORE CLOUD COVER IN PLACE. THAT BEING SAID
STILL WENT ABOVE GUIDANCE FOR TOMORROW AS THE AIRMASS ON A WHOLE
REMAINS UNCHANGED.

NUMERICAL GUIDANCE AND PROBABILISTIC QPF GUIDANCE SHOW THE MAIN
SHOWERY ACTIVITY WITH THE COLD FRONT, AGAIN WELL TO OUR WEST
TOMORROW, HOLDING OFF THROUGH THE DAYTIME. THEREFORE WE KEEP
TOMORROW DRY.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
THE BIG WEATHER STORY OF THE WEEK IS GOING TO BE THE STRONG COLD
FRONT AND ASSOCIATED PRECIPITATION TO BEGIN THE LONG TERM PERIOD.

OVERVIEW...THERE IS MUCH BETTER MODEL AGREEMENT TODAY WITH THE
TIMING AND TRACK OF THIS COLD FRONT, WITH THE TREND GENERALLY
TOWARDS A MORE PROGRESSIVE SOLUTION. STILL EXPECTING STRONG
SOUTHERLY/SOUTHWESTERLY FLOW TO DEVELOP IN THE WARM SECTOR, AND WITH
THAT WIDESPREAD PRECIPITATION AHEAD OF THE FRONT. THE FRONT IS NOW
EXPECTED TO COMPLETELY PUSH THROUGH THE REGION BETWEEN 18Z TUESDAY
AND 00Z WEDNESDAY. THERE MAY BE A BRIEF PERIOD (LESS THAN 6 HR) OF
PRECIPITATION BEHIND THE FRONT, BUT CONSIDERING THE SOURCE REGION OF
THE POLAR AIR MASS, EXPECT CONSIDERABLE DRY AIR ADVECTION BEHIND THE
FRONT.

HEAVY RAIN...MODELS CONTINUE TO SHOW MAXIMUM PRECIPITABLE WATER
VALUES AROUND 1.5 INCHES...OR ABOUT 2 STANDARD DEVIATIONS ABOVE
NORMAL FOR THIS TIME OF THE YEAR. IN ADDITION, THE 0-6KM MEAN FLOW
TUESDAY NIGHT CONTINUING INTO TUESDAY MORNING IS NEARLY PARALLEL TO
THE APPROACHING FRONT, INCREASING THE RISK FOR TRAINING STORMS.
HOWEVER, WARM CLOUD LAYER IS MARGINAL FOR AN ENHANCED HEAVY RAIN
THREAT, PWAT VALUES ACTUALLY DECREASE BEFORE THE MAXIMUM LIFT
ARRIVES OVER THE REGION, AND WITH THE TREND TOWARDS A FASTER COLD
FRONT THE PERIOD FOR HEAVY RAIN POTENTIAL IS SHORTER THAN PREVIOUSLY
EXPECTED. WILL CONTINUE WITH SIMILAR WORDING IN THE HWO HIGHLIGHTING
THE POTENTIAL FOR HEAVY RAIN AND POSSIBLE BRIEF POOR STREET DRAINAGE
FLOODING.

THUNDERSTORMS...MODELS DEPICT MARGINAL ML CAPE VALUES (<100 J/KG) IN
THE WARM SECTOR. HOWEVER, THERE IS POTENTIAL FOR ELEVATED
INSTABILITY AS WELL THROUGH THE ENTIRE PERIOD THAT THE REGION IS IN
THE WARM SECTION.

WINTRY MIX OF PRECIPITATION BEHIND THE FRONT...AS MENTIONED PREVIOUSLY,
EXPECT THE PERIOD OF PRECIPITATION BEHIND THE FRONT TO BE RATHER
BRIEF. THE HIGHER TERRAIN OF THE POCONOS COULD SEE SOME WINTRY MIX
THROUGH THIS PERIOD, BUT GIVEN WARM GROUND TEMPERATURES, DO NOT
EXPECT MUCH IN THE WAY OF ACCUMULATION. AT THIS TIME OUR GRIDS
HAVE LESS THAN 1 INCH. WPC PROBABILISTIC GUIDANCE HAS A SMALL CHC
OF 1 INCH OF SNOW OCCURRING VCNTY THE POCONOS. THE 15Z/31 SREF
PROB FOR 1 INCH OF SNOW VCNTY KMPO IS ABOUT 60 PCT.

WIND TUESDAY AFTERNOON...CONFLICTING INFORMATION. THE 12Z AND 18Z
GFS IS MORE SUBDUED THAN THE 12Z AND 18Z NAM REGARDING SOUTHERLY
FLOW WIND GUSTS. THE GUIDANCE WILL NEED TO BE MONITORED AND HOPEFULLY
THE THE SUBDUED GFS VERSION WILL BE MORE ACCURATE AND GUSTS WONT
EXCEED 30 KT. THE NAM IS MUCH MORE ROBUST...OFFERING OPPORTUNITY
FOR SOUTHERLY FLOW WIND GUSTS OF 40-45 KT FROM WESTERN MONMOUTH
COUNTY NJ SOUTHWEST THROUGH BURLINGTON COUNTY INTO DELAWARE.

WIND TUESDAY NIGHT...COMBINATION OF STRONG CAA AND ASSTD STRONG 3
HRLY PRES RISES OF POSSIBLY 6 MB IN 3 HRS OFFERS OPPORTUNITY FOR
WIDESPREAD 30-35 KT WIND GUSTS WITH ISOLATED 40 KT GUSTS POSSIBLE
THE ENTIRE CWA.


WEDNESDAY AND THURSDAY...EXPECT THE SURFACE RIDGE TO BE THE DOMINANT
FEATURE FOR THE REGION. EXPECT ONLY A MODEST WARMING TREND
THROUGH THIS PERIOD MAINLY DUE TO AIR MASS MODIFICATION.

BEGINNING THURSDAY, WE`RE WATCHING AN UPPER LEVEL THROUGH DIGGING
SOUTHEAST OVER THE GREAT BASIN REGION. THAT MUCH THE MODELS AGREE
ON. BY FRIDAY MODEL DIFFERENCES AND ENSEMBLE SPREAD INCREASE
CONSIDERABLY. THE GFS SHOWS THE TROUGH CUTTING OFF, DEEPENING AND
INTENSIFYING IN THE THE NORTHERN STREAM, EVENTUALLY PROPAGATING TO
THE GREAT LAKES REGION. WITH THIS SOLUTION, OUR REGION COULD BE IN
THE WARM SECTOR, WITH STEADY RAIN THROUGH THE WEEKEND. THE ECMWF ON
THE OTHER HAND, CUTS OFF THE LOW IN THE SOUTHERN STREAM, AS IT
PROPAGATES OFF THE COAST OF THE CAROLINAS BY SUNDAY. THIS WOULD
RESULT IN COOLER CONDITIONS, AND ONLY A BRIEF PERIOD OF
PRECIPITATION FOR MOST OF OUR REGION. CONSIDERING THE LOW
CONFIDENCE, HAVE STAYED CLOSE TO THE PREVIOUS FORECAST AND WPC
GUIDANCE THROUGH THIS PERIOD.

&&

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

THIS EVENING - TONIGHT...MOSTLY VFR THOUGH MOST OF THE NIGHT. WIND
GUSTS HAVE DIMINISHED FOR MOST SITES NOW THAT DAYTIME MIXING HAS
SUBSIDED AFTER THE SUN HAS SET. ANY PLACES THAT REMAIN GUSTY EARLY
THIS EVENING, EVEN CLOSER TO THE COAST WHERE WINDS ARE THE
STRONGEST, SHOULD LOSE THEIR GUSTINESS WITHIN THE NEXT HOUR OR
TWO.

THERE IS STILL A QUESTION ABOUT HOW MUCH STRATUS FORMS TONIGHT.
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR MOSTLY STRATUS
TO FORM OVERNIGHT TOWARD DAYBREAK MONDAY NEAR THE TOP OF THE
INVERSION, SO WE NOW HAVE MVFR CIGS AND VSBYS FOR ALL SITES TOWARD
THE PRE-DAWN HOURS AND AROUND DAYBREAK MONDAY..

TOMORROW...ANY STRATUS/FOG THAT DOES FORM LATE TONIGHT SHOULD
LIFT/BURN OFF BY MID-MORNING. SOUTHERLY WINDS WILL PICK UP AGAIN
AND BEGIN TO GUST, SLIGHTLY STRONGER, TOMORROW AFTERNOON.

OUTLOOK...

MONDAY NIGHT AND TUESDAY...DETERIORATING CONDITIONS TO WIDESPREAD
MVFR AND POSSIBLY WIDESPREAD IFR. RAIN COULD BE HEAVY AT TIMES, AND
ISOLATED THUNDERSTORMS ARE POSSIBLE DURING THE DAY TUESDAY.

LLWS IS FLAGGED IN THE WIND SHEAR GUI WITH SUSTAINED SOUTH WIND 15-20
KT AND 2000 FT WIND 200 DEGREES AT 55-60 KT FOR A FEW HRS TUE AFTN.

TUESDAY NIGHT...ALL TAF SITES SHOULD SEE NW WIND GUST 30-35 KT WITH
ISOLATED 40 KT GUST POSSIBLE.

WEDNESDAY THROUGH THURSDAY NIGHT...GENERALLY VFR CONDITIONS EXPECTED.

&&

.MARINE...
WIND GUSTS HAVE PICKED UP ALONG THE COAST LATE THIS AFTERNOON AND
THIS EVENING AND SHOULD CONTINUE INTO MONDAY. SEAS SHOULD ALSO
RESPOND, ALTHOUGH THEY NOT YET, TO THE BETTER SOUTHERLY SURGE
COMING MONDAY AHEAD OF THE APPROACHING COLD FRONT. WINDS HAVE NOT
BEEN EXTREMELY GUSTY ON THE DELAWARE BAY, SO THE ADVISORY ON THE
BAY MAY BE ABLE TO BE ALLOWED TO EXPIRE AT MIDNIGHT, BEFORE WINDS
INCREASE AGAIN ON MONDAY.

OUTLOOK...
TUESDAY...SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY. A COLD FRONT
WILL MOVE THROUGH LATE TUESDAY AFTERNOON BRINGING AN ABRUPT SHIFT
FROM SOUTHERLY TO NORTHWESTERLY WINDS. ISOLATED SOUTHERLY FLOW GALE
FORCE GUSTS POSSIBLE. THERE IS A BETTER CHC OF NW FLOW GALE FORCE
GUSTS OF 35 TO 40 KT AT TIMES TUESDAY NIGHT IN STRONG COLD AIR
ADVECTION WITH STRONG PRESSURE RISES. A GALE WATCH MAY BE
NEEDED...ESPECIALLY FOR TUESDAY NIGHT/EARLY WEDNESDAY.

WEDNESDAY...SMALL CRAFT ADVISORY CONDITIONS LIKELY...ESPECIALLY
EARLY IN THE DAY, BUT EXPECT WINDS TO DECREASE WEDNESDAY
AFTERNOON.

WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...WINDS NEAR OR JUST BELOW
25KT. HOWEVER, WAVE HEIGHTS COULD BE ABOVE 5 FT THROUGH THE ENTIRE
PERIOD.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ450>455.
     SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ430-431.

&&

$$
SYNOPSIS...JOHNSON
NEAR TERM...HEAVENER/ROBERTSON
SHORT TERM...HEAVENER
LONG TERM...DRAG/JOHNSON
AVIATION...DRAG/HEAVENER/JOHNSON/ROBERTSON
MARINE...DRAG/HEAVENER/JOHNSON




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