Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 271934
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
334 PM EDT SUN JUL 27 2014

.SYNOPSIS...
AN AREA OF LOW PRESSURE WILL MOVE OUT OF PENNSYLVANIA TONIGHT AND
LIFT INTO NEW ENGLAND MONDAY, PULLING A COLD FRONT ACROSS THE AREA.
HIGH PRESSURE WILL BEGIN MOVING INTO THE AREA LATER TUESDAY, AND
REMAIN IN CONTROL OF THE WEATHER FOR THROUGH THE END OF THE UPCOMING
WEEK.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
THE GFS INITIALIZATION CONTINUES TO LOOK SLIGHTLY BETTER AT 500MB
BUT ITS CONVECTIVE FEEDBACK OF VORT MAXES WHILE ON ONE LEVEL
CORRECT CONTINUE TO MAKE IT DIFFICULT TO FOLLOW THE MODEL. NEAR AND
SHORT TERM SOLUTION ARE AN ECMWF/HI RES ARW BLEND AS THE FORMER HAS
VERIFIED THE SYNOPTIC SCALE SHORT WAVES BETTER AND THE LATTER WAS
USED FOR CONVECTIVE ADJUSTMENTS AS ITS VERIFYING WELL AT 18Z.

COSPA VERIFYING TOO SLOW WITH CONVECTION LEAVING OHIO AND TOO NORTH
WITH WV CONVECTION. IT...RAP AND HRRR ALL DEVELOP CONVECTION OVER
THE ALLEGHENIES AND ADVECT IT EAST AHEAD OF ONGOING CONVECTION OVER
OH/PA BORDER ASSOCIATED WITH THE STRONG SHORT WAVE. SPC ANALYSIS IS
SHOWING 2000J ML CAPE IN THAT AREA AND THE STABILITY OF WAVE CLOUDS
ON VIS SATL OVER THAT AREA IS NOW GONE. SO WE WILL CONT TO START
GRIDS WITH LOW POPS THAT WILL INCREASE WITH TIME THIS EVENING.

POPS ARE TIED CLOSE TO THE ARW AND ALSO THE DEEPER LAYER MASS OMEGA
FIELDS BY THE MODELS. IN SPITE OF QPF TIMING DIFFERENCES, THE OMEGA
FIELDS TIMING ARE CLUSTERED CLOSER. THIS REMAINS A DYNAMIC SCENARIO
WITH A NEGATIVE TILT TROF AND EVEN A JET COUPLET OVER OUR CWA FOR A
WHILE OVERNIGHT. EVENTUALLY THE MLCAPE WILL DECREASE, EVEN THOUGH
THERE WILL BE NO END TO THE PREDICTED BULK SHEAR AVERAGING AROUND
40KTS. SO THE STRONGER (SEVERE?) POTENTIAL WITH THE THUNDER MAY
LINGER LONGER INTO THE NIGHT. LAST COUPLE OF COSPAS DONT CORROBORATE
THIS. FOR NOW, WE CARRIED SOME ENHANCED WORDING PAST MIDNIGHT. GIVEN
THE NEGATIVE TILT FLAVOR OF THE TROF, WHILE RAIN WILL BE HEAVY, IT
SHOULD BE PROGRESSIVE. WITH FFG VALUES RUNNING AT TYPICALLY HIGH
SUMMER LEVELS, SEVERE THREAT REMAINS OUR MORE FOCUSED CONCERN.

WE WERE SLOW WITH DROPPING TEMPS THIS EVENING AND TRIED TO TIME THE
DROP TO THE ONSET OF HEAVIER RAIN. MIN TEMPS NOT THAT FAR FROM STAT
GUIDANCE.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
SHORT WAVES ROTATING AROUND THE ANOMALOUS STRONG 500MB TROF WILL
PASS ACROSS OUR CWA ON MONDAY. CONVECTIVE TEMPS (SELF DESTRUCT
SUNSHINE) WILL BE REACHED EASY AND EARLY. THE OVERALL FCST CAPE AND
INSTAB ALOFT ON THE BIG THREE MODELS ARE NOT UNSTABLE ENOUGH FOR
THUNDER. OTHER THAN SOME EARLY THUNDER NORTHEAST CWA, WE KEPT IT AS
SHOWERS WITH HIGHEST POPS NORTHWEST THE REST OF THE DAY.

STAT GUIDANCE FOR MAX TEMPS APPEARS TOO HIGH IN THE SERN CWA UNLESS
THE COLD FRONT IS 2-4HRS SLOWER THAN PROGGED. WE WERE LOWER THAN GFS
MOS THERE AND CLOSE TO A STAT GUIDANCE BLEND ELSEWHERE.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
A MOSTLY DRY START TO THE LONG TERM FORECAST, WITH PRECIPITATION
CHANCES INCREASING LATER IN THE WEEK INTO THE WEEKEND.

THERE MAY BE SOME LINGERING SHOWERS MONDAY EVENING AS THE FRONT
CONTINUES TO PUSH OFFSHORE AND THE MID-LEVEL TROUGH LIFTS OUT, BUT
ANY PRECIPITATION IS EXPECTED TO END BY MIDNIGHT.

MUCH OF THE UPCOMING WEEK IS EXPECTED TO REMAIN MOSTLY DRY AS PW
VALUES DROP TO AN INCH OR LOWER FOR TUESDAY AND WEDNESDAY, BUT MAY
RETURN TO 1-1.25 INCHES FOR THURSDAY AND NEAR 1.5 INCHES FOR FRIDAY.
HIGH PRESSURE AT THE SURFACE WILL BUILD ACROSS THE REGION, WHILE THE
BROAD MID/UPPER TROUGH REMAINS IN PLACE ACROSS MUCH OF THE EASTERN
HALF OF THE COUNTRY. THERE AREA NO SIGNIFICANT SHORT WAVE/VORTICITY
IMPULSES THAT ARE FORECAST TO MOVE THROUGH FOR MUCH OF THE WEEK, BUT
WITH THE TROUGH IN PLACE AND DAYTIME HEATING, THERE COULD BE ENOUGH
DAYTIME INSTABILITY TO CREATE ISOLATED SHOWERS OR THUNDERSHOWERS FOR
THE LATTER HALF OF THE WEEK. EACH DAY THE CHANCES INCREASE SLIGHTLY
AND EXPAND IN COVERAGE. HOWEVER, WE DO NOT HAVE MORE THAN A SLIGHT
CHANCE PROBABILITY THROUGH FRIDAY AT THIS TIME.

AS WE MOVE INTO NEXT WEEKEND, WE GET A MORE SOLID RETURN OF MOISTURE
ACROSS THE AREA AS PW VALUES REBOUND O 1.25-1.5 INCHES. WE ALSO HAVE
A BETTER CHANCE OF VORTICITY IMPULSES AFFECTING OUR AREA WITHIN THE
SOUTHWEST FLOW ALOFT, AND WITH THE COASTAL FRONT TRYING TO PUSH BACK
CLOSER TO SHOWER, WE MAY HAVE A FOCUS FOR PRECIPITATION TO FORM.
THEREFORE THE PRECIPITATION CHANCES INCREASE INTO NEXT WEEKEND.

TEMPERATURES THROUGH THE EXTENDED ARE FORECAST TO BE CLOSE TO OR
SLIGHTLY BELOW NORMAL.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

18Z TAFS HAVE A HIGH CONVECTIVE IMPACT DURING THIS EVENING INTO
THE EARLY OVERNIGHT ACROSS THE TERMINALS AND AIRPORTS.

REST OF THIS AFTERNOON. VFR WITH CUMULUS CLOUDS EXPANDING AND SOME
CIRRUS ABOVE THEM SOUTH. NO THUNDER MENTIONED ALTHOUGH SOME ISOLATED
THUNDER MIGHT FORM BEFORE THE ORGANIZED SYSTEM. LOWEST CONFIDENCE
ABOUT NO THUNDER IN PA. PLEASE WATCH FOR POSSIBLE AMENDMENTS. WINDS
ARE SLOWLY BACKING TO THE SOUTHWEST AND MAY EVEN GO SOUTH AT SPEEDS
OF AROUND 10 KTS.

THIS EVENING, EXPECTING A LINE OF STRONG TSTMS TO MOVE THROUGH THE
AREA. HIGHEST CONFID AT KABE AND KRDG. LOWEST AT KMIV AND KACY. A
EARLY TIMING HEDGE WAS MAINTAINED (MOST LIKELY TIME IS TOWARD THE
MIDDLE OF THE TEMPO GROUP).  MVFR TO BRIEFLY IFR (BECAUSE OF
BREVITY NOT INCLUDED) CONDITIONS LIKELY ALONG WITH GUSTY WEST
WINDS.

OVERNIGHT PREVAILING MVFR CONDITIONS EXPECTED TO CONTINUE DURING
SHOWERS. ISOLATED THUNDER POSSIBLE, BUT CONFIDENCE TOO LOW AS TO
WHERE OR WHEN TO INCLUDE. WINDS WILL BE LIGHTER, GENERALLY FROM
THE SOUTH. IMPROVEMENT TOWARD MORNING AS PCPN ENDS. THINKING TOO
MUCH WIND FOR SGFCNT FOG TO FORM.

MONDAY MORNING, VFR CONDITIONS WITH A CUMULUS BASED CIG OCCURRING.
GUSTY WEST WINDS, ESPECIALLY FOR JULY, WITH SUSTAINED SPEEDS
AROUND 15 KTS AND GUSTS TO AROUND 25 KTS. SOME WIDELY SCATTERED
SHOWERS SHOULD START DEVELOPING TOWARD THE END OF THE CURRENT TAF
FCST PERIOD. GREATEST CONFIDENCE NORTH, REASON FOR NOW LEFT OUT OF
KPHL TAF.

OUTLOOK...
MONDAY NIGHT-WEDNESDAY NIGHT...MAINLY VFR
THURSDAY-FRIDAY...MAINLY VFR. ISOLATED SHOWERS/THUNDERSTORMS
POSSIBLE BOTH AFTERNOONS, ESPECIALLY FRIDAY.

&&

.MARINE...
A SMALL CRAFT ADVISORY WILL BE ISSUED FOR TONIGHT AND MONDAY FOR THE
OCEAN WATERS. ONE WILL BE ISSUED FOR DELAWARE BAY FOR MONDAY. FIRST
FOR THE LIKELIHOOD THAT SEAS REACH 5 FEET THIS EVENING AND THEN THE
LIKELIHOOD OF NON CONVECTIVE WEST WIND GUSTS REACHING THE CRITERIA
ON DELAWARE BAY AS WELL AS THE OCEAN WATERS DURING THE DAY ON
MONDAY. WAVE WATCH GUIDANCE BRINGS SIX FOOT SEAS AS IS INTO OUR
COASTAL WATERS, SHAVING A FOOT OR SO OFF WOULD STILL GET US THERE
TONIGHT. TOUGH NIGHT AS IT IS WITH THUNDERSTORMS EXPECTED. ON MONDAY
MORE OF THE GUSTINESS MAY BE CONCENTRATED AROUND THE INLETS AND IN
DELAWARE BAY WITH POSSIBLY LESS GUSTINESS FARTHER OFFSHORE. THE
GRADIENT AND WINDS SHOULD START RELAXING LATER IN THE DAY ON MONDAY.

OUTLOOK...
MONDAY NIGHT-FRIDAY...SMALL CRAFT ADVISORY CONDITIONS POSSIBLE EARLY
MONDAY NIGHT, SUBSIDING AND REMAINING BELOW ADVISORY LEVELS THROUGH
THE PERIOD.

&&

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

&&

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




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