942  
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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