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Area Forecast Discussion
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000
FXUS61 KPHI 281957
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
357 PM EDT MON JUL 28 2014

.SYNOPSIS...
LOW PRESSURE MOVING INTO NEW ENGLAND THIS EVENING IS SHOVING A COLD 
FRONT OFF THE MID ATLANTIC COAST. WEAK HIGH PRESSURE WILL FOLLOW 
LATER TUESDAY THROUGH WEDNESDAY. IT THEN MERGES INTO THE WESTERN
ATLANTIC HIGH PRESSURE SYSTEM LATE THIS WEEK. MEANWHILE...THE
FRONT WILL BE LURKING JUST OFF THE COAST AS A STATIONARY FRONT.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
THE COLD FRONT IS APPROACHING OUR NORTHWESTERN ZONES LATE THIS 
AFTERNOON AND WILL PROGRESS ACROSS THE CWA THIS EVENING AND SHOULD 
PASS COMPLETELY THROUGH BY MIDNIGHT. A LINE OF SHOWERS AND VERY 
ISOLATED THUNDERSHOWERS HAVE FORMED ALONG THE FRONT THIS AFTERNOON. 
ALL OF THE GUIDANCE INDICATES THE SHOWERS/THUNDER DISSIPATING AND/OR 
WEAKENING AS THEY REACH OUR AREA THIS EVENING AS THE MID-LEVEL 
TROUGH LIFTS TO OUR NORTHEAST. THERE WILL BE ANOTHER SHORT 
WAVE/VORTICITY IMPULSES MOVE INTO THE AREA ALONG WITH THE COLD 
FRONT, SO THERE IS THE POSSIBILITY THE SHOWERS COULD MAINTAIN 
THEMSELVES ACROSS A PORTION OF THE AREA. THEREFORE WE WILL KEEP 
ISOLATED SHOWERS INTO THE EVENING FROM THE DELAWARE VALLEY 
NORTHWARD, BUT WE END EVERYTHING BY MIDNIGHT.

AFTER THE SHOWERS END, CLOUDS SHOULD SCATTER OUT OVERNIGHT, BUT HOW 
MUCH THEY SCATTER WILL DETERMINE HOW COOL IT GETS TONIGHT. FOR NOW 
WE USED A BLEND OF MAV/MET MOS AND MOSGUIDE WHICH DROPS EVERYONE 
SEVERAL DEGREES COOLER THAN LAST NIGHT AND ENDS UP BEING SEVERAL 
DEGREES BELOW NORMAL.

WINDS WILL REMAIN GUSTY INTO THIS EVENING, BUT THE GUSTS SHOULD DROP 
OFF AFTER SUNSET THROUGH THE OVERNIGHT HOURS. WESTERLY WINDS AHEAD 
OF THE COLD FRONT WILL SWITCH TO MORE NORTHWESTERLY BEHIND IT.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
A NICE TUESDAY AHEAD AS COOLER, DRIER AIR CONTINUES TO MOVE IN 
ACROSS THE AREA AS WEAK HIGH PRESSURE BEGINS TO BUILD IN FROM THE 
WEST. WITH PW VALUES BELOW ONE INCH AND NO SIGNIFICANT SHORT 
WAVE/VORTICITY IMPULSES, TUESDAY IS EXPECTED TO BE DRY ACROSS THE 
AREA.

TEMPERATURES WILL BE COOLER THAN THE LAST COUPLE OF DAYS AS 925/850 
MB TEMPS AND THICKNESSES DECREASE INTO TUESDAY. USED A BLEND OF 
MAV/MET MOS, MOSGUIDE, AND MIXED 925 MB TEMPS FOR HIGHS ON TUESDAY 
WHICH ENDS UP BEING SEVERAL DEGREES BELOW NORMAL.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
500 MB: A LARGE TROUGH IN THE EAST WILL SLOWLY WEAKEN LATE THIS
WEEK INTO EARLY NEXT WEEK.

TEMPERATURES: ABOUT 5 DEGREES BELOW NORMAL WEDNESDAY WARMING TO
NEAR NORMAL THIS COMING WEEKEND AND EARLY NEXT WEEK.

FORECAST BASIS: UNLESS OTHERWISE NOTED THE LONG TERM PERIOD OF THIS 
FORECAST IS GENERALLY BASED ON A 50 50 BLEND OF THE 12Z/28 NAM/GFS 
MOS FOR THE PERIOD TUESDAY NIGHT - WEDNESDAY NIGHT... THE 12Z/28 GFS 
MOS THURSDAY AND THURSDAY NIGHT AND THEN THEREAFTER (FRIDAY ONWARD) 
THE 1522Z/28 WPC GRIDDED GUIDANCE FOR ALL ELEMENTS EXCEPT HAVE 
APPLIED THE WARMER 12Z/28 MEXMOS TEMPS. ALL THIS WAS CHECKED
AGAINST THE 12Z/28 ECMWF TO ENSURE WE'RE IN THE BALLPARK (BARRING
MIDDAY OVC SKIES AND RAIN) WITH ECMWF CYCLICALLY PERSISTENT 18Z
2METER TEMPERATURES. THE PRECIPITATION PROBABILITY GUIDANCE WAS
CHECKED AGAINST THE 09Z/28 SREF POPS FOR .01 IN 3 HRS THROUGH 00Z
FRIDAY AND THEREAFTER THE 12Z/28 GEFS 6HR POPS FOR 0.05 .


THE DAILIES...
IT SORT OF LOOKS LIKE WE'RE PRIMARILY IN A WEAK SURFACE RIDGE
REGION THIS 6 DAY PERIOD AND NOT FAVORABLE FOR MUCH RAIN. 

BASICALLY FOR NOW ITS A GENERALLY FAIR WEATHER FORECAST THIS 6 DAY
PERIOD. 

THERE IS A CHANCE FOR LATE DAY OR EVENING CONVECTION NE PA
AND NW NJ LATER IN THE WEEK BUT FOR NOW IS CHANCEY AND LOW
CONFIDENCE.

AS FOR THE LURKING QUASI STATIONARY ALONG THE COAST... IT MAY DRIFT
CLOSER TO THE SHORE BY THE WEEKEND AS A WARM FRONT WITH ITS
CONVECTION POSSIBLY SPREADING ASHORE BUT CONFIDENCE FOR THIS
SCENARIO IS ALSO BELOW AVERAGE.

IT DOES APPEAR THIS QUASI STATIONARY BOUNDARY WILL EVENTUALLY
DISSIPATE AND AS IT DOES...HIGHER HUMIDITY SHOULD SLOWLY RETURN TO
THE AREA LATE THIS WEEKEND INTO EARLY NEXT WEEK.

TEMPERATURES AND POPS AS DESCRIBED ABOVE IN THE FORECAST BASIS.

&&

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

MOSTLY VFR CONDITIONS EXPECTED ACROSS THE TAF SITES THROUGH TONIGHT 
AND INTO TUESDAY. A LINE OF SHOWERS/ISOLATED THUNDERSHOWERS HAVE 
DEVELOPED ALONG A COLD FRONT THAT WILL MOVE ACROSS THE AREA THIS 
EVENING THROUGH MIDNIGHT. MODEL GUIDANCE INDICATES THE 
SHOWERS/THUNDER WILL DISSIPATE/WEAKEN AS IT MOVES INTO OUR AREA THIS 
EVENING, HOWEVER, WE HAVE INCLUDED A TEMPO SHOWER GROUP FOR THE 
DELAWARE VALLEY TAFS THIS EVENING, AND ENDED UP ADDING A TEMPO 
THUNDERSTORM GROUP FOR ABE/RDG THIS EVENING. IT'S POSSIBLE THAT 
VSBYS MAY BRIEFLY DROP TO 5SM OR LESS, MAINLY FOR ABE/RDG, SO ADDED 
IT IN FOR THESE TWO SITES. THE REST WERE LESS CONFIDENT, SO LEFT 
THEM OUT FOR NOW. 

WESTERLY WINDS GUSTING 20-25 KNOTS WILL CONTINUE THROUGH SUNDOWN, 
THEN THE GUSTS SHOULD DROP OFF, AND WINDS WILL BECOME NORTHWESTERLY 
BEHIND THE COLD FRONT OVERNIGHT INTO TUESDAY. WINDS MAY BEGIN 
SWITCHING TO WEST OR SOUTHWEST AGAIN BY LATE TUESDAY INTO TUESDAY 
EVENING, AND A SEABREEZE MAY FORM ALONG THE COAST BY THE AFTERNOON.

OUTLOOK...
TUESDAY NIGHT-WEDNESDAY NIGHT...MAINLY VFR. 
THURSDAY-SATURDAY...MAINLY VFR. ISOLATED SHOWERS/THUNDERSTORMS POSSIBLE
EACH DAY BUT LOW CONFIDENCE ON OCCURRENCE. PATCHY IFR FOG OR
STRATUS IS POSSIBLE FRI NIGHT.

&&

.MARINE...
THE SMALL CRAFT ADVISORY FOR THE DELAWARE BAY AND THE SOUTHERN HALF 
OF THE ATLANTIC COASTAL WATERS WAS EXTENDED THROUGH MIDNIGHT TONIGHT 
AS WINDS ARE GUSTING AROUND 25-30 KNOTS NOW, AND SHOULD CONTINUE 
INTO THE EVENING AHEAD OF THE FRONTAL BOUNDARY. AS THE FRONTAL 
BOUNDARY MOVES THROUGH, THE GUSTS WILL SWITCH FROM WEST TO NORTHWEST 
AND DROP OFF SLIGHT, AND SEAS SHOULD LOWER AS WELL. THE SEAS MAY 
REMAIN LONGER ON THE NORTHERN WATERS A FEW MORE HOURS, SO WE LEAVE 
THE NORTHERN HALF ENDING AT 6 AM TUESDAY.

OUTLOOK...
TUESDAY NIGHT-SATURDAY...NO HEADLINES ANTICIPATED. LOOKS LIKE GOOD
WEATHER FOR BEING ON THE WATERS IN THIS TIME FRAME.

WE ARE MONITORING THE GFS OPERATIONAL RUN DEPICTION (FOR SEVERAL
FORECAST CYCLES) OF A TROPICAL SYSTEM IN THE ATLANTIC BASIN FOR
EARLY NEXT WEEK BUT THE ECMWF OPERATIONAL VERSION STILL DOESNT
HAVE IT.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ430-431-
     452>455.
     SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ450-451.

&&

$$
SYNOPSIS...DRAG 356
NEAR TERM...ROBERTSON
SHORT TERM...ROBERTSON
LONG TERM...DRAG/ROBERTSON 356
AVIATION...DRAG/ROBERTSON 356
MARINE...DRAG/ROBERTSON 356






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