118  
FXUS61 KPHI 281501  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
1101 AM EDT WED SEP 28 2016  
   
SYNOPSIS
 
 
AN AREA OF LOW PRESSURE WILL MOVE ACROSS THE OHIO RIVER VALLEY  
AND COMBINE WITH ANOTHER LOW ACROSS THE CENTRAL AND SOUTHERN  
APPALACHIANS THURSDAY INTO FRIDAY. THIS LOW WILL LIFT BACK ACROSS  
THE OHIO RIVER VALLEY AND INTO THE EASTERN GREAT LAKES REGION  
SATURDAY INTO SUNDAY AND BRING A FRONTAL SYSTEM ACROSS OUR AREA.  
HIGH PRESSURE IS THEN EXPECTED TO BUILD ACROSS THE NORTHEAST LATE  
MONDAY INTO TUESDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
1040 AM: CEILINGS 800 TO 1800 FT SPREADING SOUTHWEST ONTO THE NJ  
COAST NOW WILL EVENTUALLY REACH PHL AROUND 19 OR 20Z. COLD AIR  
DAMMING MINIMAL TODAY SINCE THE BIG PUSH OF COOL MOIST BOUNDARY  
LAYER AIR DOESN'T ARRIVE MOST OF OUR FCST AREA UNTIL AFTER MAX  
HEATING TODAY. COLD AIR DAMMING DOES BECOME A MUCH BIGGER PLAYER  
TOMORROW. GUSTY E-NE WIND 20-30 MPH DEVELOPS BY THIS AFTERNOON.  
 
SHOWERS AND ISOLATED EMBEDDED TSTMS MD E SHORE AND W DE INTO  
EXTREME SW NJ WITH DIMINISHING INTENSITY SO THE 1040 AM POP  
ADJUSTMENT WAS TO ACCOUNT FOR THE MID LEVEL RAIN DYING OUT  
MIDDAY/EARLY THIS AFTERNOON. WHILE WAS NOT EXACTLY SURE HOW TO  
HANDLE THIS CHES BAY ORGANIZED SYSTEM THAT DUMPED 3-4.5" ON THE  
OTHER SIDE OF THE BAY AND 1-2" PARTS OF THE MD E SHORE, IT IS ON  
THE WANE.  
 
WE HAVE SEEN THE SPC EXPANDED MARGINAL RISK INTO MD E SHORE BUT NO  
ACTION AT THIS TIME FOR ENHANCED WORDING. WILL REEVALUATE WITH 12Z  
GFS GUIDANCE. NAM HAS NOT HANDLED THIS SYSTEM VERY WELL SO AM  
INCLINED TO FAVOR GGEM/GFS/EC/UK/WPC BLEND.  
 
FORECAST SOUNDINGS SUPPORT A DEEP ENOUGH MOIST LAYER FOR AT LEAST  
PATCHY DRIZZLE TO DEVELOP LATE THIS AFTERNOON, TOWARD THE NJ COAST.  
 
HIGH TEMPERATURES RANGE FROM THE MID/UPPER 60S ALONG AND NORTH OF  
THE I-80 CORRIDOR TO MID/UPPER 70S ACROSS SOUTHEASTERN PA,  
SOUTHERN NJ AND DELMARVA.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/
 
 
THE UPPER LOW IS FORECAST TO SLOW DOWN OVER THE MIDWEST STATES  
TONIGHT AS IT BECOMES CUTOFF. HIGH PRESSURE WILL CONTINUE TO  
REMAIN ANCHORED TO OUR NORTH WHILE THE FRONTAL BOUNDARY REMAINS  
STALLED TO OUR SOUTH. THE EASTERLY LOW-LEVEL JET BETWEEN THESE  
SYSTEMS OVER THE MID ATLANTIC WILL STRENGTHEN FURTHER TO AROUND 40  
KT.  
 
EXPECT SHOWERS TO EXPAND NORTHEASTWARD ACROSS THE ENTIRE AREA  
TONIGHT. EXPECT FOR THE NAM-BASED GUIDANCE, MODELS CONTINUE TO  
SHOW A BAND OF HEAVY RAINFALL DEVELOPING VERY CLOSE TO THE WESTERN  
MOST ZONES OF OUR CWA. THE TREND HAS BEEN TO SHIFT THE AXIS OF  
HIGHER QPF FARTHER SOUTH AND WEST, LIKELY AS MODELS ARE MORE  
ACCURATELY CAPTURING THE MAGNITUDE OF THE COLD-AIR DAMMING  
PATTERN. ADDITIONALLY, WITH THE GREATEST LOW-LEVEL CONVERGENCE  
SITUATED AT NOSE OF THE LOW-LEVEL JET FORECAST TO BE POSITIONED TO  
OUR WEST, THE GREATEST RISK FOR EXCESSIVE RAINFALL MAY REMAIN ON  
THE WESTERN SIDE OF THE CHESAPEAKE BAY. QPF AMOUNTS OF 1-2 INCHES  
ARE FORECAST FOR EASTERN MD AND OUT TOWARD CHESTER/BERKS CO. IN  
EASTERN PA. WE OPTED TO NOT ISSUE A FLOOD WATCH AT THIS JUNCTURE.  
 

 
   
LONG TERM /THURSDAY THROUGH TUESDAY/
 
 
UNSETTLED WEATHER CONTINUES TO BE FORECAST THROUGH THE FIRST HALF  
OF THE EXTENDED PERIOD, WITH GENERALLY FAIR WEATHER FOR THE SECOND  
HALF OF THE PERIOD.  
 
FOR THURSDAY INTO FRIDAY, AN AREA OF LOW PRESSURE AT THE SURFACE  
WILL BE LOCATED TO OUR SOUTHWEST, WHILE HIGH PRESSURE REMAINS TO  
OUR NORTHWEST. IN BETWEEN, A STATIONARY BOUNDARY WILL BE LOCATED  
JUST TO OUR SOUTH. THIS WILL KEEP AN ONSHORE FLOW ACROSS OUR AREA.  
MEANWHILE, A CLOSED LOW ALOFT WILL BE SPINNING TO OUR WEST AS  
WELL. THIS WILL KEEP A PERSISTENT SOUTHERLY FLOW ALOFT ACROSS THE  
AREA AT THE SAME TIME. WITH THE SOUTHERLY FLOW ALOFT, OVERRUNNING  
PRECIPITATION IS EXPECTED TO CONTINUE AREA WITHIN THE ONSHORE FLOW  
THURSDAY AND FRIDAY. IT WILL NOT LIKELY RAIN THE ENTIRE TIME, BUT  
SEVERAL PERIODS OF RAIN WILL BE ASSOCIATED WITH SEVERAL SHORT  
WAVES/VORTICITY IMPULSES ROUNDING THE CLOSED LOW ALOFT TO OUR  
WEST.  
 
BY SATURDAY, AND ESPECIALLY SUNDAY, THE HIGH TO OUR NORTH BEGINS  
TO MOVE EASTWARD, AND THE LOW TO OUR WEST WILL BEGIN LIFTING BACK  
TOWARD THE GREAT LAKES REGION. THIS WILL EVENTUALLY PULL THE  
FRONTAL BOUNDARY TO OUR SOUTH ACROSS OUR AREA ON SUNDAY. THERE  
WILL CONTINUE TO BE A CHANCE OF SHOWERS SATURDAY THROUGH SUNDAY AS  
SEVERAL SHORT WAVE/VORTICITY IMPULSES MOVE ACROSS THE AREA AS THE  
CLOSED LOW ALOFT BEGINS TO BREAK DOWN AND LIFT TO THE NORTHEAST.  
 
BY MONDAY INTO TUESDAY, THE SURFACE LOW AND LOW ALOFT PASS TO OUR  
EAST, AND DRIER AIR BEGINS TO MOVE INTO THE AREA AS HIGH PRESSURE  
TRIES TO MOVE IN FROM THE NORTH. THE HIGH MAY REMAIN TO OUR NORTH,  
TUESDAY WHICH COULD PRODUCE AN ONSHORE FLOW WHICH MAY END UP  
LEADING TO MORE CLOUD COVER AND COOLER CONDITIONS FOR TUESDAY.  
 

 
   
AVIATION /15Z WEDNESDAY THROUGH SUNDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
THIS AFTERNOON...VFR CONDITIONS TO START. CIGS 1000-2200 FEET ADVECT-  
DEVELOP SOUTHWESTWARD FM THE NJ NOW AND SPREAD WEST TO PHL BY 18Z.  
SHOWERS VCNTY KILG AND KMIV MAY REACH PHL BUT THESE SHOWERS ARE  
TENDING TO DRY OUT AS THEY MOVE NORTHEAST. DRIZZLE MAY DEVELOP  
KACY LATE IN THE DAY. LIGHT N-NE WIND EARLY THIS MORNING BECOMES  
GUSTY NORTHEAST 20-28 KT BY THIS AFTERNOON.  
 
TONIGHT...WIDESPREAD CIGS 700-1700 FT WITH VSBY OCCASIONALLY AOB  
3 MI IN STRATUS, MIST AND FOG WITH SHOWERS. NE WIND WITH SCATTERED  
GUSTS 20 KT.  
 
OUTLOOK...  
 
THURSDAY-SATURDAY...A PROLONGED PERIOD OF MVFR OR IFR CONDITIONS  
WITH PERIODS OF RAIN IS EXPECTED TO AFFECT THE TAF SITES THROUGH  
THE PERIOD. EAST TO NORTHEAST WINDS ARE EXPECTED TO GUST 20-25  
KNOTS FOR MUCH OF THE AREA.  
 
SATURDAY NIGHT-SUNDAY...SOME IMPROVEMENT, POSSIBLY TO VFR BY SUNDAY.  
SHOWERS REMAIN POSSIBLE.  
 

 
   
MARINE
 
 
SCA IN EFFECT FOR THE NJ COAST. A GALE WATCH WAS PREVIOUSLY IN  
EFFECT FOR ANZ450/451 FOR TONIGHT BUT WE DO NOT ANTICIPATE GALES  
TO DEVELOP BEFORE THURSDAY. WINDS OF 15- 25 KT ARE EXPECTED WITH  
GUSTS TO 30 KT THROUGH TONIGHT ALONG THE NJ COAST. SEAS IN THE  
COASTAL ATLANTIC WATERS WILL SUBSEQUENTLY BUILD TO 5-7 FT BY  
TONIGHT. SCA CONTINUES WITH A 6 PM START FOR DE BAY AND THE  
ATLANTIC DE WATERS THOUGH COULD SEE A SOONER START.  
 
OUTLOOK...  
THURSDAY...GALE WATCH IN EFFECT FOR THE NORTHERN HALF OF THE  
ATLANTIC COASTAL WATERS. SMALL CRAFT ADVISORY IN EFFECT ELSEWHERE.  
 
THURSDAY NIGHT...GALE WATCH IN EFFECT FOR ALL AREAS.  
 
FRIDAY...GALE FORCE WINDS MAY REMAIN ACROSS THE NORTHERN HALF OF THE  
ATLANTIC COASTAL WATERS. SMALL CRAFT ADVISORY LEVEL WINDS MAY REMAIN  
ELSEWHERE.  
 
FRIDAY NIGHT-SATURDAY...WINDS EXPECTED TO DROP BELOW SMALL CRAFT  
ADVISORY LEVELS, HOWEVER, SEAS MAY REMAIN ABOVE ADVISORY LEVELS  
THROUGH THE PERIOD.  
 
SATURDAY NIGHT-SUNDAY...WINDS AND SEAS EXPECTED TO DROP BELOW SMALL  
CRAFT ADVISORY LEVELS.  
 
RIP CURRENTS...  
THERE CONTINUES A MODERATE RISK FOR THE FORMATION OF DANGEROUS  
RIP CURRENTS TODAY AS PER A RECHECK OF THE ENE SUSTAINED WIND  
~18KT AND DOMINANT 4 SECOND SHORT PERIOD SWELL.  
 
THURSDAY: THE PROBABILITY FOR THE FORMATION OF DANGEROUS RIP  
CURRENTS IS AT LEAST MODERATE TO PERHAPS HIGH.  
 

 
   
TIDES/COASTAL FLOODING
 
 
A PERSISTENT ONSHORE FLOW IS EXPECTED FOR THE REST OF THE WEEK  
INTO THE WEEKEND. THE STRONGEST WINDS ARE EXPECTED THURSDAY THROUGH  
FRIDAY. TIDES LEVELS ARE FORECAST TO INCREASE THROUGH THIS PERIOD,  
AND WE COULD REACH MINOR COASTAL FLOOD LEVELS.  
 

 
   
CLIMATE
 
 
WILL ADD EXTENSIVE CLIMATE INFORMATION LATE THIS MORNING OR THIS  
AFTERNOON AS TIME PERMITS.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...GALE WATCH FROM THURSDAY EVENING THROUGH LATE THURSDAY NIGHT  
FOR ANZ430-431-452>455.  
SMALL CRAFT ADVISORY UNTIL 6 PM EDT THURSDAY FOR ANZ452-453.  
GALE WATCH FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT  
FOR ANZ450-451.  
SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY FOR ANZ450-451.  
SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 PM EDT  
THURSDAY FOR ANZ430-431-454-455.  
 

 
 

 
SYNOPSIS...ROBERTSON  
NEAR TERM...DRAG/KLEIN 1101  
SHORT TERM...KLEIN  
LONG TERM...ROBERTSON  
AVIATION...DRAG/KLEIN/ROBERTSON 1101  
MARINE...DRAG/KLEIN/ROBERTSON 1101  
TIDES/COASTAL FLOODING...  
CLIMATE...  
 
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