678  
FXUS61 KPHI 181007  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
607 AM EDT FRI APR 18 2014  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL CONTINUE TO EXTEND ACROSS THE EASTERN SEABOARD  
THROUGH TODAY. THE HIGH WILL RETREAT AS A WEAKENING FRONTAL BOUNDARY  
MOVES ACROSS THE AREA TONIGHT INTO SATURDAY MORNING. HIGH PRESSURE  
REESTABLISHES ITSELF ACROSS EASTERN CANADA OVER THE WEEKEND AND  
BUILDS SOUTHWARD ALONG THE EASTERN SEABOARD SUNDAY INTO MONDAY.  
ANOTHER FRONTAL BOUNDARY IS EXPECTED TO AFFECT THE AREA NEXT  
TUESDAY, FOLLOWED BRIEFLY BY HIGH PRESSURE WEDNESDAY NIGHT INTO  
THURSDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
630 AM ESTF...LITTLE CHANGE TO THE PRIOR 230-3AM AFD UPDATE.  
 
EARLY THIS MORNING THROUGH 8AM...CLOUDY AND 35-40F EXCEPT I78 NORTH  
WHERE IT PARTIALLY CLEARED WITH 27-33F TEMPS AT 6AM. CLOUDS AT 6AM  
ARE FILLING IN RAPIDLY. A LIGHT NE-E WIND CONTINUES.  
 
ELY MARINE LAYER OF HIGH RH SATURATING JUST BELOW THE INVERSION  
AROUND 1800-2400 FT. NOT NEARLY AS COLD AS THURSDAY MORNING WHEN A  
RECORD LOW WAS SET AT ALLENTOWN PA.  
 
TODAY...FCST BASIS IS MOSTLY NAM 3RLY TEMPS AND MAX TEMP DURING THE  
DAY AND THE HIGHER OF THE NCEP 3 HRLY MOS DEWPOINTS. 50 50 BLENDED  
SFC SUSTAINED WINDS.  
 
LOW CLOUDS RECEDE EWD AS THE BL WARMS BUT LOW CLOUDS SHOULD DOMINATE  
MOST IF NOT ALL OF THIS FRIDAY MORNING THROUGH MIDDAY. THEN  
CONSIDERABLE HIGH CLOUD DURING MID AND LATE AFTN. E WIND GUST NEAR  
15 MPH WITH THE WIND BECOMING S-SE LATE IN THE DAY. MAX TEMPS NEAR  
5 PM THIS AFTN IN THE INTERIOR AS THE LOW CLOUDS DISSIPATE DURING  
THE AFTN AND TEMPS MAY RISE 5 DEGREES BETWEEN 2P AND 5P VCNTY  
PHILADELPHIA.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/
 
 
TONIGHT...FCST BASIS IS A 50 50 BLEND OF THE 00Z/18 NCEP MOS GUIDANCE  
WITH THE COLDER OF THE LOW TEMPS NEAR 10Z/SAT.  
 
CONSIDERABLE HIGH CLOUD THIS EVENING WITH CFP SCT-BKN SC NEAR 4000  
FT TOWARD DAWN SATURDAY. LIGHT SE-S WIND DURING THE EVENING TURN W  
OR NW LATE AT NIGHT.  
 

 
   
LONG TERM /SATURDAY THROUGH THURSDAY/
 
 
WE EXPECT DRY WEATHER TO BUILD IN ACROSS THE AREA SATURDAY BEHIND  
THE WEAKENING FRONTAL BOUNDARY THAT WILL CROSS THE AREA EARLY  
SATURDAY MORNING AS HIGH PRESSURE BEGINS TO BUILD SOUTHWARD OUT OF  
CANADA. THE HIGH SHOULD SUPPRESS THE LOW TO OUR SOUTH OFF THE  
SOUTHEAST COAST WHICH SHOULD PREVENT ANY PRECIPITATION FROM REACHING  
OUR AREA.  
 
THIS HIGH WILL REESTABLISH ITSELF ACROSS EASTERN CANADA AND BUILD  
SOUTHWARD ALONG THE EASTERN SEABOARD SUNDAY AND MONDAY. THIS WILL  
CONTINUE TO PROVIDE DRY WEATHER OVER THE WEEKEND INTO MONDAY OF NEXT  
WEEK. WITH SLIGHT RIDGING ALOFT TAKING PLACE, TEMPERATURES WILL  
RETURN CLOSER TO NORMAL OVER THE WEEKEND INTO EARLY NEXT WEEK.  
SUNDAY WILL LIKELY BE THE COOLEST DAY WHEN THICKNESSES AND 925 MB  
TEMPERATURES ARE AT THEIR LOWEST.  
 
THE HIGH WILL WEAKEN AND RETREAT MONDAY NIGHT AHEAD OF AN  
APPROACHING STORM SYSTEM. AN AREA OF LOW PRESSURE IS FORECAST TO  
MOVE OUT OF THE GREAT LAKES REGION AND STRENGTHEN AS IT MOVES INTO  
NEW ENGLAND TUESDAY INTO TUESDAY NIGHT. AS THIS OCCURS, A COLD  
FRONT WILL SWEEP THROUGH THE AREA LATE TUESDAY INTO TUESDAY NIGHT,  
WHICH WILL BRING THE NEXT CHANCE OF PRECIPITATION ACROSS THE AREA.  
THEREFORE WE MAINTAIN CHANCE POPS ACROSS THE AREA DURING THIS TIME  
PERIOD.  
 
THIS LOW IS EXPECTED TO SLOWLY PULL TO OUR NORTHEAST THROUGH  
WEDNESDAY AND THURSDAY AS HIGH PRESSURE BEGINS TO BUILD SOUTHWARD  
OUT OF CANADA ONCE AGAIN. WEDNESDAY AND THURSDAY ARE EXPECTED TO BE  
DRY, BUT SHOULD BE QUITE GUSTY WITH THE TIGHTENING PRESSURE  
GRADIENT. WINDS COULD EASILY GUST 25-30 MPH, IF NOT HIGHER.  
 

 
   
AVIATION /10Z FRIDAY THROUGH TUESDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
THROUGH 12Z...CIGS MOSTLY 1600-2400 FT. LIGHT EAST WIND.  
 
AFTER 12Z...THE MVFR CIG IS EXPECTED TO DISSIPATE RAPIDLY EASTWARD  
MIDDAY WITH A VFR CIRRUS DECK ABOVE IT DURING THE AFTERNOON.  
SYNOPTIC SCALE WINDS OVERALL SHOULD BE LIGHTER (GENERALLY AN EASTWARD  
COMPONENT) THAN THURSDAY AND A SEA BREEZE FRONT MAY FORM DURING  
THE AFTERNOON AS THE WIND TENDS TO TURN SE-S.  
 
TONIGHT...VFR CIRRUS WITH CHC OF A SCT-BKN DECK NEAR 4000 FT TOWARD  
10Z SATURDAY ASSOCIATED WITH A WEAK COLD FRONTAL PASSAGE (CFP).  
 
OUTLOOK...  
SATURDAY-MONDAY NIGHT...MOSTLY VFR. GUSTY N-NW WINDS 15-20 KNOTS  
SATURDAY.  
 
TUESDAY...MVFR CONDITIONS POSSIBLE WITH SHOWERS WITH A FRONTAL  
PASSAGE.  
 

 
   
MARINE
 
 
SEAS 7 FT AT 44009 AT 5 AM.  
 
GFS WW4 GUIDANCE HAS BEEN TOO LOW BY A FOOT OR 2 ON THE ATLANTIC  
WATERS AND SO RAISED THAT GUIDANCE THRU THIS FRIDAY EVENING.  
 
SCA CONTINUES OPEN ATLC WATERS...MAINLY FOR SEAS AND HAVE CONVERTED  
THAT SCA HEADLINE TO SCA FOR HAZARDOUS SEAS HERE AT THE 3 AM ISSUANCE.  
 
DE BAY WATERS NO HEADLINE THRU TONIGHT. E-NE WIND G 15 KT AND SEAS  
LESS THAN 3 FT TODAY. WINDS AND SEAS DIMINISH/SUBSIDE TONIGHT. THE  
WIND TURN S TOWARD SUNSET THEN SHIFTS TO W OR NW TOWARD DAWN SATURDAY.  
 
OUTLOOK...  
SATURDAY...SUB-SMALL CRAFT ADVISORY CRITERIA EXPECTED, THOUGH  
WINDS MAY GUST NEAR 20 KNOTS.  
 
SATURDAY NIGHT-SUNDAY NIGHT...WINDS AND SEAS INCREASING TO SMALL CRAFT  
ADVISORY CRITERIA OVERNIGHT SATURDAY AND CONTINUE INTO SUNDAY. SEAS  
MAY REMAIN ELEVATED INTO SUNDAY NIGHT.  
 
MONDAY-MONDAY NIGHT...A RETURN TO SUB-SMALL CRAFT ADVISORY CRITERIA.  
 
TUESDAY...FRONTAL PASSAGE EXPECTED WITH NEAR ADVISORY CONDITIONS.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 AM EDT  
SATURDAY FOR ANZ450>455.  
 

 
 

 
SYNOPSIS...ROBERTSON  
NEAR TERM...DRAG 607A  
SHORT TERM...DRAG 607A  
LONG TERM...ROBERTSON  
AVIATION...DRAG/ROBERTSON 607A  
MARINE...DRAG/ROBERTSON 607A  
 
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