056  
FXUS61 KPHI 011941  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
341 PM EDT SAT OCT 1 2016  
   
SYNOPSIS
 
 
PERSISTENT LOW PRESSURE THAT HAS BEEN SITTING TO OUR WEST THE LAST  
FEW DAYS WILL FINALLY START TO LIFT NORTHEAST AS IT WEAKENS. BY  
MONDAY, THE LOW WILL BE OVER NEW ENGLAND, AND THE ASSOCIATED COLD  
FRONT WILL SLIDE THROUGH OUR REGION. A SURFACE HIGH WILL BUILD AND  
STAY NORTH OUR OUR REGION THROUGH MUCH OF THE REMAINDER OF THE WORK  
WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
 
 
A CLOSED LOW, WHICH HAS BEEN STUCK IN THE UPPER OHIO VALLEY, IS  
FORECAST TO SLOWLY MOVE INTO THE EASTERN GREAT LAKES REGION TONIGHT.  
MEANWHILE, HIGH PRESSURE AT THE SURFACE UP ACROSS NORTHERN NEW  
ENGLAND TO THE CANADIAN MARITIMES HAS BEEN LOCKED IN, HOWEVER THIS  
FEATURE WILL GRADUALLY WEAKEN AND SHIFT EASTWARD TONIGHT.  
 
THIS WILL CONTINUE WITH AN ONSHORE FLOW TONIGHT, HOWEVER IT HAS  
WEAKENED. THERE REMAINS A PRONOUNCED LOW-LEVEL INVERSION WITH  
EASTERLY FLOW BELOW IT WHICH THEN VEERS TO SOUTHERLY ABOVE IT.  
THIS IS LOCKING IN THE LOW CLOUDS ACROSS THE AREA AND AT TIMES HAS  
PRODUCED SOME DRIZZLE. THERE IS A WEAK SURFACE LOW TRACKING  
NORTHWARD, ESPECIALLY JUST OFFSHORE, HOWEVER THERE IS AN AREA OF  
DIFFLUENT FLOW ALOFT BETWEEN IT AND THE CLOSED LOW. THIS ALONG WITH  
JUST ENOUGH LIFT UP AND OVER THE MARINE LAYER IS RESULT IN SOME  
SHOWERS LIFTING NORTHWARD THIS AFTERNOON. THESE ARE ANTICIPATED TO  
CONTINUE TO GRADUALLY LIFT NORTH AND NORTHWESTWARD THROUGH THIS  
EVENING. SOME INSTABILITY TO OUR SOUTH, NEAR AND SOUTH OF A FRONTAL  
ZONE, COULD RESULT IN A FEW THUNDERSTORMS, HOWEVER WE ARE  
ANTICIPATING THESE TO WEAKEN AS THEY ENCOUNTER THE DEEPER MARINE  
LAYER. SOME CLEARING IS APPROACHING SOUTHERN DELAWARE LATE THIS  
AFTERNOON, HOWEVER OVERALL WE ARE EXPECTING THE LOW CLOUDS TO HANG  
ON. OTHERWISE, SOME ADDITIONAL DRIZZLE CANNOT BE RULED OUT THROUGH  
THE NIGHT. WE KEPT SOME POPS IN THROUGH THE NIGHT DUE TO THE CHANCE  
OF AT LEAST SOME ADDITIONAL SHOWERS.  
 
GIVEN THE WEALTH OF LOW-LEVEL MOISTURE IN PLACE COMBINED WITH A  
LESSENING WIND FIELD SHOULD YIELD TO SOME FOG DEVELOPMENT. IT IS NOT  
ALL THAT CLEAR IF THIS BECOMES DENSE GIVEN THE STRATUS THAT IS IN  
PLACE. THE FOG SHOULD BE MORE WIDESPREAD IN THE HIGHER TERRAIN,  
HOWEVER WIDESPREAD DENSE FOG IS NOT CURRENTLY EXPECTED MAINLY DUE TO  
THE EXPECTED STRATUS DECK TO BE MAINTAINED.  
 
AS FOR THE LOW TEMPERATURES, WE USED A BLEND OF MOSTLY CONTINUITY  
AND MOS. THE HOURLY TEMPERATURE AND DEW POINT GRIDS WERE ADJUSTED  
BASED ON THE LATEST OBS, THEN THE LAMP/LAV GUIDANCE WAS BLENDED INTO  
THIS EVENING.  
 

 
   
SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/
 
 
THE PESKY CLOSED LOW IS FORECAST TO SLOWLY SHIFT NORTHEASTWARD FROM  
THE EASTERN GREAT LAKES DURING THE COURSE OF SUNDAY. AS ADDITIONAL  
SHORT WAVE ENERGY CONTINUES TO MOVE AROUND THIS CLOSED LOW, SOME  
SHOWERS SHOULD BE AROUND DURING THE DAY. THE DAY HOWEVER SHOULD  
START OUT WITH SOME FOG AND/OR DRIZZLE. THE FLOW SHOULD START TO  
TRANSITION DURING SUNDAY, THEREFORE ALLOWING SOME POSSIBLE DRYING  
WORKING IN FROM THE SOUTH. AS THIS OCCURS, THE CLOUD BASES SHOULD  
LIFT SOME ESPECIALLY ACROSS THE SOUTHERN AREAS WITH PERHAPS EVEN  
SOME BREAKS OF SUNSHINE DURING THE AFTERNOON. IF THIS OCCURS,  
AFTERNOON TEMPERATURES ARE EXPECTED TO BE WARMER ESPECIALLY AS THE  
ONSHORE FLOW LESSENS A BIT MORE. OVERALL, SOME IMPROVEMENT IS  
EXPECTED BUT WE DID NOT RUSH IN THE PARTIAL CLEARING. HIGH  
TEMPERATURES WERE A BLEND OF MOS AND CONTINUITY WITH SOME LOCAL  
TWEAKS MADE, WHICH RESULTED IN SOME LOWERING OF THE HIGHS FOR MANY  
AREAS.  
 

 
   
LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/
 
 
OVERVIEW...THE PERIOD STARTS WITH THE OCCLUDED/COLD FRONT OFF THE NJ  
AND DE COASTS AND A STACKED LOW PRESSURE SYSTEM OVER THE GREAT  
LAKES. ON MONDAY, THE MID-LEVEL LOW WILL CONTINUE TO WEAKEN AND OPEN  
UP AS IT MAKES IT'S WAY SOMEWHERE BETWEEN ALBANY AND PHILADELPHIA.  
ON TUESDAY THIS FEATURE IS FORECAST TO DRIFT OFF THE COAST. COME  
WEDNESDAY, SURFACE HIGH PRESSURE WILL BE IN CONTROL FROM MAINE DOWN  
TO THE GULF COAST WITH A HIGH AMPLITUDE RIDGE ABOVE IT. HIGH  
PRESSURE IS FORECAST TO REMAIN IN CONTROL THROUGH FRIDAY. AT THE  
SAME TIME ON FRIDAY, WELL TO OUR SOUTH, HURRICANE MATTHEW IS  
FORECAST TO BE OVER THE BAHAMAS. FOR SATURDAY, CONFIDENCE IS HIGHER  
THAT THE TROF CURRENTLY OFF THE PACIFIC NORTHWEST COAST WILL BE  
SOMEWHERE OVER EASTERN NORTH AMERICA. A COLD FRONT WILL BE ATTACHED  
TO IT. THE LESSER KNOWN IS HOW STRONG IT WILL BE, WHERE IT WILL  
EXACTLY ALIGN UP, AND HOW IT WILL AFFECT/HELP STEER MATTHEW.  
 
TEMPERATURES...FOR REFERENCE, NORMALS FOR PHILADELPHIA FOR THE  
PERIOD ARE IN THE AROUND/LOW 70S AND LOW/MID 50S. THROUGH THE  
PERIOD, OVERNIGHT LOWS ARE FORECAST TO BE ABOVE NORMAL. DAYTIME  
HIGHS ARE FORECAST TO BE ABOVE NORMAL EARLY IN THE PERIOD AND THEN  
AT OR BELOW NORMAL FOR THE REST OF IT.  
 
PRECIPITATION...WE'LL SEE A DIMINISHING THREAT OF SHOWERS SUNDAY  
NIGHT. BY MONDAY, SMALL POPS HAVE BEEN PAINTED FOR THE JUST THE  
NORTHERN AREAS. ON TUESDAY, SMALL POPS WERE REINTRODUCED CWA-WIDE AS  
THE MID-LEVEL LOW WORKS OFF THE COAST. UNCERTAINTY EXISTS FOR  
WEDNESDAY THROUGH FRIDAY WITH THE QUESTION BEING HOW STRONG DOES THE  
ONSHORE FLOW BECOME AND HOW MUCH LOW LEVEL MOISTURE WORKS IT'S  
WAY ONSHORE. SATURDAY'S LOW CONFIDENCE FORECAST TAKES INTO ACCOUNT  
THE APPROACHING COLD FRONT, MID-LEVEL TROF, AND MATTHEW.  
 
WINDS...BENIGN IS A GOOD ADJECTIVE WITH MAINLY LIGHT NORTHWEST WINDS  
DEVELOPING MONDAY. THIS WILL BE SHORT-LIVED AS THE SURFACE FLOW WILL  
GO MORE NORTHEASTERLY ON TUESDAY AND THEN PERSIST INTO THE WEEKEND.  
THIS LOOKS TO BE A LONG DURATION NE EVENT WITH SCA OR GALE FORCE  
WINDS/WIND GUSTS ALONG THE COAST.  
 
IMPACTS...NOTHING MUCH TO SPEAK OF EARLY IN THE PERIOD, BUT  
DEPENDING ON HOW THINGS UNFOLD, THERE COULD BE SOME COASTAL IMPACTS  
LATER IN THE WEEK IF THE NE FLOW INCREASES AS FORECAST.  
 

 
   
AVIATION /20Z SATURDAY THROUGH THURSDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
REST OF THIS AFTERNOON...CEILINGS MAINLY RANGING BETWEEN 500-1000  
FEET. SOME SHOWERS AROUND WILL LOCALLY REDUCE THE VISIBILITY TO  
MVFR, ALTHOUGH SOME DRIZZLE ESPECIALLY AT ACY WILL LOWER THE  
VISIBILITY. NORTHEAST WINDS MOSTLY AROUND 10 KNOTS.  
 
TONIGHT...IFR/LIFR CEILINGS AS LOW CLOUDS PERSIST. SOME SHOWERS OR  
DRIZZLE AROUND WITH EVEN SOME FOG DEVELOPING, WHICH WILL ALL REDUCE  
THE VISIBILITY AT TIMES. AS OF NOW, WIDESPREAD FOG BELOW 1SM IS NOT  
ANTICIPATED GIVEN THE STRATUS IN PLACE. NORTHEAST WINDS BECOMING  
MAINLY 5 KNOTS OR LESS.  
 
SUNDAY...IFR/LIFR CONDITIONS TO START SHOULD IMPROVE TO MVFR DURING  
THE AFTERNOON. IF ENOUGH DRYING IS ABLE TO WORK IN DURING THE  
AFTERNOON, CEILINGS COULD RISE TO VFR ESPECIALLY SOUTH AND EAST OF  
PHL. NORTHEAST TO EAST WINDS 4-8 KNOTS.  
 
OUTLOOK...  
 
SUNDAY NIGHT THROUGH TUESDAY...MOSTLY VFR CONDITIONS EXPECTED. SMALL  
CHANCE OF SHOWERS WITH MVFR CONDITIONS SUNDAY AND TUESDAY.  
 
WEDNESDAY AND THURSDAY...CONDITIONS LOWERING TO IFR FOR DELAWARE  
VALLEY AND COASTAL PLAIN TERMINALS AS AN ONSHORE FLOW RESULTS IN LOW  
STRATUS CLOUDS. THESE CONDITIONS ARE FORECAST TO PERSIST INTO  
THURSDAY.  
 

 
   
MARINE
 
 
THE ONSHORE FLOW IS WEAKENING AS HIGH PRESSURE TO THE NORTH IS  
TENDING TO SHIFT A BIT FARTHER FROM OUR AREA, ALLOWING THE PRESSURE  
GRADIENT TO RELAX. AS A RESULT, THE SMALL CRAFT ADVISORY FOR THE  
LOWER DELAWARE BAY IS CANCELLED. THE ADVISORY CONTINUES THROUGH 06Z  
TONIGHT FOR THE ATLANTIC COASTAL WATERS ZONES AS SEAS REMAIN IN THE  
4-7 FOOT RANGE, ALTHOUGH THESE GRADUALLY SUBSIDING. THE CONDITIONS  
ARE THEN EXPECTED TO BE BELOW ADVISORY CRITERIA ON SUNDAY. THE  
SENSIBLE WEATHER FEATURES SOME SHOWERS AND/OR DRIZZLE WITH PERHAPS  
SOME FOG AT TIMES.  
 
OUTLOOK...  
 
SUNDAY NIGHT AND MONDAY...WINDS AND SEAS SHOULD STAY BELOW SCA  
CRITERIA.  
 
TUESDAY THROUGH THURSDAY...WINDS AND SEAS ARE EXPECTED TO BUILD  
THROUGH THE DAY TUESDAY, AND SCA CONDITIONS COULD DEVELOP AS EARLY  
AS MIDDAY TUESDAY AND PERSIST INTO THURSDAY. GALE FORCE GUSTS  
POSSIBLE WEDNESDAY AND THURSDAY.  
 

 
   
TIDES/COASTAL FLOODING
 
 
THE HIGH TIDE TONIGHT LOOKS TO FALL SHORT OF ADVISORY CRITERIA AS IT  
IS THE LOWER TIDE. DESPITE THE DEPARTURES HOLDING UP SOME, THE FLOW  
HAS WEAKENED ALONG WITH THE SEAS, THEREFORE THE NEXT HIGH TIDE ON  
SUNDAY SHOULD ALSO FALL SHORT OF ADVISORY CRITERIA.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT SUNDAY FOR ANZ450>455.  
 

 
 

 
SYNOPSIS...JOHNSON/KRUZDLO  
NEAR TERM...GORSE  
SHORT TERM...GORSE  
LONG TERM...KRUZDLO  
AVIATION...GORSE/KRUZDLO  
MARINE...GORSE/KRUZDLO  
TIDES/COASTAL FLOODING...GORSE  
 
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