Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 011958
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
358 PM EDT SAT AUG 1 2015

.SYNOPSIS...
A HIGH PRESSURE SYSTEM OVER THE LOWER OHIO VALLEY WILL SLOWLY MOVE
SOUTHEAST THROUGH MONDAY. THE NEXT COLD FRONT FROM THE GREAT LAKES
IS EXPECTED TO CROSS OUR REGION LATE MONDAY INTO EARLY TUESDAY,
EVENTUALLY STALLING JUST SOUTH OF OUR AREA WEDNESDAY AND THURSDAY
AS A WAVE OF LOW PRESSURE MOVES ALONG IT. THE FRONTAL BOUNDARY
IS FORECAST TO REMAIN NEARLY STATIONARY TO THE SOUTH OF THE
DELMARVA PENINSULA ON FRIDAY AND SATURDAY AS ADDITIONAL WAVES OF
LOW PRESSURE MOVE ALONG IT.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A WEAK SURFACE TROUGH/FRONTAL BOUNDARY WILL CONTINUE TO PUSH FURTHER
OFFSHORE TONIGHT WHILE HIGH PRESSURE STARTS TO BUILD IN FROM THE
WEST.

ISOLATED SHOWERS CONTINUE TO SPORADICALLY DEVELOP DUE TO THE DAYTIME
HEATING AND A COUPLE OF WEAK SHORT WAVES ALOFT. A FEW RUMBLES OF
THUNDER ARE POSSIBLE IF UPDRAFTS BECOME STRONG ENOUGH WITH SOME
SHOWERS, BUT ANY ACTIVITY IS EXPECTED TO BE ISOLATED. AS THE SUN
BEGINS TO SET, AND DAYTIME INSTABILITY IS LOST, SHOWER ACTIVITY WILL
DIMINISH AS WELL. THE EXCEPTION TO THIS IS OVERNIGHT, GENERALLY
GENERALLY AROUND OR SHORTLY AFTER MIDNIGHT, AN AREA OF SHOWERS MAY
DEVELOP ACROSS SOUTHERN NEW JERSEY AND THE CENTRAL/SOUTHERN
DELMARVA. A WEAK SHORT VORTICITY IMPULSE IS FORECAST TO SLIDE ACROSS
THE AREAS, HELPING TO ENHANCE LIFT AS THE TROUGH/FRONTAL BOUNDARY
SLIDES FURTHER OFFSHORE. THE MAJORITY OF MODEL GUIDANCE INDICATES
THIS POTENTIAL, SO WE`LL INSERT A FEW HOURS OF ISOLATED SHOWERS IN
THE FORECAST.

LOW TEMPERATURES ARE A BLEND OF MAV/MET MOS.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
HIGH PRESSURE BUILDS TO OUR SOUTHWEST, WITH OUR AREA ON THE
NORTHEAST SIDE OF THE HIGH. PW VALUES ARE FORECAST TO DROP BELOW ONE
INCH, AND WITH NO SHORT WAVE/VORTICITY IMPULSES, SUNDAY IS EXPECTED
TO BE A PRECIPITATION FREE DAY.

TEMPERATURES SUNDAY ARE EXPECTED TO BE A DEGREE OR TWO LOWER THAN
SATURDAY FOR MANY LOCATIONS, ALTHOUGH HIGHS ARE STILL FORECAST TO BE
ABOVE NORMAL. HIGH TEMPERATURES ARE A BLEND OF MIXED 925MB ECMWF
TEMPERATURES, MAV/MET MOS, AND MOSGUIDE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
A HOT START AND RELATIVELY COOL AND WETTER LOOKING FINISH TO THE
LONG TERM. THE DETAILS THOUGH AS TO WHAT OCCURS AFTER WE GET THERE
REMAINS MUDDLED. BOTH THE WRF-NMM AND GFS HAD A VERY GOOD 500MB
INITIALIZATION WITH THE GFS SLIGHTLY BETTER AT 850MB AND THE WRF-
NMMB NOTICEABLY BETTER AT 925MB (GFS WARM BIAS). THE GFS DP/DT
GENERALLY SHOWS A FLATTER TROF IN THE EAST AND BROADER RIDGE OUT
WEST, WITH DECENT RUN TO RUN CONTINUITY.

TO THAT END, THE 12Z OP GFS LOOKED MORE IN SYNC WITH THE GEFS MEAN
THAN THE 06Z RUN DID. BUT THE MEDIUM RANGE MODELS REMAIN AT ODDS
AS TO HOW ENERGY FROM THE PACIFIC TROF WILL TRANSLATE OVER THE WRN
NOAM RIDGE INTO THE ERN NOAM TROF. THERE HAS BEEN LITTLE RUN TO
RUN CONTINUITY OR CONSISTENCY BETWEEN MODELS. DEVELOPING
CONVECTIVE SYSTEMS AND THEIR PREDECESSOR AND/OR EMERGING SHORT
WAVES SEEM TO BE THE DRIVERS OF THIS. BUT AT THIS POINT ITS
DIFFICULT TO DIFFERENTIATE BETWEEN FEEDBACK MCV(S) AND LEGITIMATE
TRIGGERS. THUS THIS PART OF THE FORECAST IS LONG ON CONTINUITY AND
SHORT ON BEING ABLE TO DIFFERENTIATE DRY WEATHER DAYS.

THE GREATEST IMPACT TO OUR WEATHER SHOULD BE A HOT DAY ON MONDAY
CLOSE TO URBAN CORRIDOR HEAT HEADLINE LEVELS, POSSIBLY STRONG STORMS
IF THEY CAN ARRIVE IN TIME ON MONDAY EVENING AND HEAVY RAIN
POTENTIAL IF ANY OF THE SUBSEQUENT WAVE OR WAVES OF LOW PRESSURE
CAN BACK INTO OUR CWA.

THE LONG TERM START RELATIVELY EASY WITH A QUIET SUNDAY NIGHT.
BECAUSE DEW POINTS HEADING INTO SUNDAY NIGHT SHOULD BE RELATIVELY
LOW AND WINDS LIGHT WITH FEW CLOUDS, WE HAVE MIN TEMPS IN OUTLYING,
MORE RURAL LOCATIONS GETTING TO RELATIVELY COMFORTABLE LEVELS.

ON MONDAY OUR CWA SHOULD SPEND MOST OF THE DAY IN A SUBSIDENCE
REGION BETWEEN THE UPWARD MOTION FROM THE APPROACHING FRONT AND
PRECIPITATION OFFSHORE ASSOCIATED WITH OUR OLD CFP FROM THURSDAY
NIGHT. PREDICTED CONVECTIVE TEMPS GET REACHED LATE IN THE DAY, SO
WE KEPT IN A LOW CHANCE "NORTHWEST" DURING THE AFTERNOON. THIS GFS
RUN IS ON THE HOT SIDE (INITIALIZED HOT TOO) OF THE ENSEMBLE
CLUSTER. OF LATE THE PREDICTED 2M TEMPS AS IS HAVE COME AS CLOSE
AS ADDING ABOUT 10C TO 925MB TEMPS. THIS KEPT OUR MAX TEMPS CLOSE
TO CONTINUITY. BECAUSE SOUTHWEST WINDS ARE EXPECTED TO INCREASE
MONDAY AFTERNOON AND THE DEEPER MOISTURE ALOFT IS STILL WEST, DEW
POINTS ARE PREDICTED TO DROP. THIS HAS AFTERNOON HEAT INDEX VALUES
TOPPING IN THE 90S (MID 90S URBAN CORRIDOR) FOR NOW.

IN TERMS OF THUNDERSTORM STRENGTH, THE CURRENT FORECAST SCENARIO
LOOKS ABOUT SIX HOURS TOO LATE TO MAXIMIZE IN OUR FORECAST AREA.
ON PAPER, THIS ONE HAS VIGOR AS THERE IS A PREDICTED EML, TT(S)
ABOVE 50 (TEMPS AT 500MB ARE RELATIVELY LOW), DCAPES ABOVE 1000J
AND BULK SHEAR VALUES NORTH OF 30 KNOTS ESPECIALLY IN THE NORTHWEST
HALF OF OUR CWA. BUT BECAUSE OF ITS LATER ARRIVAL TIME AND ALSO
BECAUSE ITS GOING INTO A LESSER SHEARED ENVIRONMENT, WE KEPT CHANCE
POPS AND DECREASED THEM TOWARD THE COAST. SOME MODELS HAVE NO
MEASURABLE SOUTHEAST OF I95 CORRIDOR.

ITS BEEN THE SUMMER OF 1000+J (WRF-NMMB) VS 0J (GFS) MIXED LAYER
CAPES AND TUESDAY IS NO EXCEPTION. THE GFS IS EXTREMELY DRY AND
VERY CONFINED WITH ITS APPROACHING VIGOROUS SHORT WAVE. WHILE THE
NAM/WRF HAS VERIFIED HOT, THE SYNOPTIC SET-UP (LOOKS TO PROBABLY BE
A SECONDARY CFP) INDICATES THAT A PRECIPITATION CHANCE BE INCLUDED.
WE KEPT LOW CHANCE IN THE FORECAST. THERE SHOULD BE A DROP IN DEW
POINTS TUESDAY, BUT WITH THE DOUBLE FRONT STRUCTURE, TEMPERATURES
SHOULD BE LOWER, BUT NOT AS MUCH OF A DROP OFF. MAX TEMPS AOA STAT
GUIDANCE.

THERE IS BETTER MODELING CONSENSUS ABOUT THE LACK OF PCPN FOR
TUESDAY NIGHT AND WEDNESDAY. WE WANT TO SEE AT LEAST ONE MORE
SOUNDING RUN BEFORE REMOVING ALL POPS. REGARDLESS OF POPS,
TEMPERATURES AND DEW POINTS WILL BE LOWER.

THEN FOR THURSDAY THROUGH SATURDAY, NO MODELS ARE KEYING ON ANY
SPECIFIC 12 HOUR PERIOD AS THE WETTEST IN UNISON. THE ONLY
CONSISTENCY IS THAT THEY ARE ALL DIFFERENT AND IF WE WENT BACK TO
THE PREVIOUS SOUNDING RUN, THEY WERE ALL DIFFERENT AGAIN. UNTIL
THIS WAVE TRAIN SETTLES, WE HAVE KEPT CHANCE POPS IN ALL THREE
DAYS. IT WOULD SEEM THAT SOUTHERN PARTS OF OUR CWA HAVE HIGHER
CHANCES AND HIGHER CHANCES OF HVYR PCPN THAN NORTH, BUT THAT IS
ABOUT AS CONFIDENT A STATEMENT AS WE CAN MAKE RIGHT NOW. THIS
FORECAST KEPT MUCH OF A CONTINUITY/WPC BLEND.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. A FEW ISOLATED
SHOWERS ARE POSSIBLE THIS AFTERNOON/EVENING, BUT CHANCES OF HITTING
A TAF SITE ARE MINIMAL SO THEY ARE NOT INCLUDED IN THE TAFS.

GUSTY WINDS AROUND 15-20 KNOTS WILL CONTINUE THIS AFTERNOON, BEFORE
GUSTS DROPPING AROUND SUNSET. WINDS MAY BECOME LIGHT AND
VARIABLE/CALM FOR MANY LOCATIONS OVERNIGHT, ALTHOUGH ANY DIRECTION
WILL LIKELY BECOME MORE NORTHWESTERLY. THE NORTHWESTERLY WINDS
AROUND 5-10 KNOTS WILL BECOME MORE WESTERLY AFTER SUNRISE SUNDAY,
THEN SOUTHWESTERLY DURING THE DAY.

OUTLOOK...
SUNDAY NIGHT THROUGH MONDAY MORNING...VFR CONDITIONS ARE EXPECTED AT
THE TERMINALS. SOME MVFR CONDITIONS AT RURAL AIRPORTS IN FOG EARLY
MONDAY.

MONDAY AFTERNOON...MAINLY VFR, BUT WITH SCATTERED SHOWERS AND
TSTMS WITH MVFR CONDITIONS LATE.

MONDAY NIGHT...PREDOMINATELY MVFR DUE TO CIG AND VSBY RESTRICTIONS
AS WELL AS FROM SCATTERED SHOWERS AND TSTMS.

TUESDAY...MAINLY VFR CONDITIONS. SOME ISOLATED TO PERHAPS SCATTERED
SHWRS/THUNDERSTORMS ARE POSSIBLE.

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...PREDOMINANTLY VFR.

THURSDAY...SOME MVFR CONDITIONS POSSIBLE DURING SHOWERS AND TSTMS.

&&

.MARINE...
SUB-SMALL CRAFT ADVISORY CONDITIONS WILL CONTINUE THROUGH SUNDAY,
ALTHOUGH WINDS WILL GUST AROUND 20 KNOTS AT TIMES THIS AFTERNOON
INTO TONIGHT.

OUTLOOK...
SUNDAY NIGHT THROUGH MONDAY MORNING...SUB-ADVISORY CONDITIONS ARE
EXPECTED.

MONDAY AFTERNOON THROUGH TUESDAY...SOME WIND GUSTS COULD BE AROUND
25 KNOTS PLUS WITH SEAS INCREASING TO AROUND SMALL CRAFT ADVISORY
CRITERIA FOR THE COASTAL WATERS LATE MONDAY INTO TUESDAY ASSOCIATED
WITH THE SOUTHWEST FLOW PRECEDING A COLD FRONT PASSAGE. MODELS
SOMETIMES INCREASE SEAS TOO QUICKLY, SO THIS MAY HOLD OFF TO
MONDAY NIGHT.

TUESDAY NIGHT THROUGH THURSDAY...SUB-SCA CONDITIONS EXPECTED.
CONFIDENCE IS MODERATE DUE TO WAVES OF LOW PRESSURE MOVING SOUTH OF
OUR FORECAST WATERS. STRONGER LOWS MIGHT BRING SMALL CRAFT ADVISORY
CONDITIONS TO THE OCEAN WATERS.

&&

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

&&

$$
SYNOPSIS...GIGI/KLINE
NEAR TERM...ROBERTSON
SHORT TERM...ROBERTSON
LONG TERM...GIGI
AVIATION...GIGI/KLINE/ROBERTSON
MARINE...GIGI/KLINE/ROBERTSON



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