556  
FXUS61 KPHI 240145  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
945 PM EDT WED SEP 23 2020  
   
SYNOPSIS
 
 
HIGH PRESSURE REMAINS IN CONTROL OF OUR WEATHER INTO THURSDAY.  
THE CENTER OF THE HIGH WILL SLOWLY SLIDE FROM THE TENNESSEE AND  
OHIO RIVER VALLEYS TO THE SOUTHEAST COAST INTO THURSDAY AS THE  
REMAINS OF TROPICAL CYCLONE BETA MOVE INTO THE SOUTHERN MID-  
ATLANTIC FRIDAY. HEADING INTO NEXT WEEK, A SERIES OF COLD FRONTS  
WILL USHER IN COOLER AIR AND WHAT LOOKS TO BE THE FIRST  
APPRECIABLE PRECIPITATION IN SEVERAL WEEKS MONDAY AND TUESDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
 
 
QUIET CONDITIONS CONTINUE THIS EVENING AND OVERNIGHT ACROSS THE  
MID ATLANTIC REGION. HIGH PRESSURE CONTINUES TO PUSH OFFSHORE OF  
THE SOUTHEAST COAST, BUT STILL NOSE ITS WAY INTO THE MID WEST  
AND MID ATLANTIC REGION. DRY WEATHER IS EXPECTED, ALTHOUGH SOME  
HIGH LEVEL CLOUDS WILL MAKE THEIR WAY ACROSS THE AREA WELL  
NORTHEAST OF A MID LEVEL LOW NEAR THE MID MISSISSIPPI VALLEY. THE  
TREND OF WARMER OVERNIGHT LOWS WILL ALSO CONTINUE WITH TONIGHT  
BEING WARMER THAN LAST NIGHT. EXPECT LOWS MAINLY IN THE 50S  
TO NEAR 60 IN SOME PLACES. THERE IS A CHANCE FOR PATCHY FOG  
LATER TONIGHT, MAINLY JUST RADIATION INDUCED GROUND FOG FOR MOST  
PLACES, SO VISIBILITIES ARE NOT EXPECTED TO DROP SIGNIFICANTLY  
FOR MOST AREAS AT THIS TIME.  
 

 
   
SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/
 
 
FOR THURSDAY, SURFACE RIDGING OVER THE SE CONUS WEAKENS AS THE  
CENTER OF HIGH PRESSURE MOVES OFF THE SE COAST INTO THE WESTERN  
ATLANTIC. MEANWHILE IN THE UPPER LEVELS THE ENERGY ALOFT  
ASSOCIATED WITH BETA WILL START TO GET SHEARED APART AS IT  
ENTERS A JET STREAK OVER THE EAST COAST AHEAD OF AN UPPER TROUGH  
CENTERED NEAR THE MIDWEST. THIS WILL ALLOW HIGH CLOUDINESS TO  
LOWER AND THICKEN THROUGH THE DAY AS MOISTURE CONTINUES TO  
ADVANCE NORTH IN THESE LEVELS BUT THERE STILL SHOULD BE AT LEAST  
SOME SUN VISIBLE THROUGH THE CLOUDS AT LEAST THROUGH THE FIRST  
PART OF THE DAY. ALSO, IT WILL REMAIN DRY IN THE LOWEST 10 TO 15  
K FT DUE TO THE INFLUENCE OF RESIDUAL SURFACE RIDGING OVER THE  
AREA SO EXPECT THE DAY TO REMAIN RAIN FREE. HIGHS WILL ONCE  
AGAIN BE MAINLY IN THE MIDDLE TO UPPER 70S WITH DEW POINTS IN  
THE 50S SO STILL NOT TOO HUMID.  
 
NOTHING CHANGES TOO MUCH FOR THURSDAY NIGHT THOUGH WE WILL HAVE  
TO WATCH AS THE NORTHERN EDGE OF DEEPER LAYER MOISTURE FROM  
BETA MAKES ITS WAY CLOSER TO THE AREA. EXPECT IT TO STILL STAY  
DRY THROUGH THE PERIOD FOR OUR CWA THOUGH SO WE KEEP POPS BELOW  
15 PERCENT.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
SEVERAL ITEMS OF INTEREST IN THE EXTENDED FORECAST. HEADING  
INTO FRIDAY, THE REMNANTS OF TROPICAL CYCLONE BETA WILL MOVE TO  
OUR SOUTH ACROSS PORTIONS OF VIRGINIA, BRINGING THE CHANCE FOR  
SOME RAINFALL TO THE SOUTHERN HALF OF THE AREA FRIDAY AND FRIDAY  
NIGHT. THE WEEKEND LOOKS QUIET AS A WEAK RIDGE OF HIGH PRESSURE  
SHIFTS EASTWARD ALONG THE EASTERN SEABOARD. MEANWHILE, A SERIES  
OF PROGRESSIVE SHORTWAVE TROUGHS WILL AMPLIFY A LONGER WAVE  
TROUGH ACROSS THE GREAT LAKES AND INTO THE NORTHEAST. OUR FIRST  
APPRECIABLE PRECIP CHANCES LOOK TO OCCUR MONDAY AND TUESDAY NEXT  
WEEK AS THIS PATTERN CHANGE ENSUES.  
 
FRIDAY'S FORECAST LOOKS A LITTLE TRICKY AS BETA REMAINS OUR  
BUGABOO PER SE. LATEST MODEL GUIDANCE HAS CONTINUED TO INCH  
NORTHWARD, AS NOTED IN THE PREVIOUS DISCUSSION. THE GFS BRINGS  
PRECIP A LITTLE FURTHER NORTH THAN THE EC, BUT GIVEN THE TREND  
AMONGST MOST OF THE GUIDANCE, THIS MAY WORK OUT. THERE IS  
SIGNIFICANT DRY AIR WORKING AGAINST THIS SYSTEM, WITH DEW POINTS  
IN THE UPPER 40S TO LOW 50S LATER THURSDAY AND FRIDAY. WENT  
WITH A NICE BLENDED APPROACH FOR POPS WITH BEST CHANCES SOUTH OF  
PHILLY-ATLANTIC CITY FOR RAIN. HIGHS IN A MIRROR OF NORMAL WITH  
UPPER 70S TO NEAR 80 ACROSS NORTHERN NEW JERSEY TO THE LOW TO  
MID 70S ACROSS DELMARVA, WHERE MORE PERSISTENT CLOUD COVER WILL  
LIMIT DAYTIME HEATING.  
 
QUIET WEATHER FOR THE WEEKEND WITH A WEAK RIDGE BUILDING ACROSS  
THE MID-ATLANTIC AS NORTHWEST FLOW BEGINS TO SET THE STAGE FOR  
A SERIES OF PROGRESSIVE SHORTWAVE PERTURBATIONS INTO EARLY NEXT  
WEEK. HIGHS TRENDING IN THE UPPER 70S TO AROUND 80.  
 
A MORE, DARE WE SAY, INTERESTING WEATHER PATTERN BEGINS TO  
EVOLVE AS WE HEAD INTO NEXT WEEK WITH THE FIRST OF TWO  
SHORTWAVES MOVING SOUTHEAST ACROSS THE GREAT LAKES AND INTO THE  
NORTHEAST MONDAY MORNING. THIS WILL DRIVE CYCLOGENESIS AS THE  
TROUGH BEGINS TO DIG AND DEVELOP A NEGATIVE TILT MONDAY. A  
SURFACE LOW LOOKS TO DEVELOP ACROSS UPSTATE NEW YORK AND WORK  
ITS WAY NORTHWARD INTO THE SAINT LAWRENCE RIVER VALLEY. A COLD  
FRONT WILL TRAIL BEHIND THIS FEATURE, BUT TIMING HAS SLOWED IN  
INTO PROGRESSION INTO OUR REGION. BEST FORCING FOR PRECIP LOOKS  
TO BE MONDAY EVENING AND OVERNIGHT, BUT THERE IS SOME  
DISAGREEMENT ON HOW EXPANSIVE PREFRONTAL PRECIPITATION WILL BE.  
HIGHS LOOK TO RANGE FROM THE MID TO UPPER 70S ACROSS THE  
FORECAST AREA.  
 
THERE ARE INDICATIONS THAT A SECONDARY SHORTWAVE WILL FURTHER  
AMPLIFY THE DEVELOPING LONG WAVE TROUGH TUESDAY INTO WEDNESDAY,  
BUT CONSIDERABLE AMBIGUITY STILL EXISTS IN HOW THIS WILL EVOLVE  
AND EXACTLY WHEN. THIS WILL LIKELY LEAD TO THE FORMATION OF  
ANOTHER SURFACE LOW AND ATTENDANT COLD FRONT TUESDAY NIGHT INTO  
WEDNESDAY. THE GFS IS A LITTLE MORE PROGRESSIVE WITH THIS  
FEATURE, BRINGING PRECIP INTO THE WESTERN PORTIONS OF THE AREA  
WEDNESDAY MORNING, WHEREAS THE EC HAS MOST OF THE ENERGY AND  
FORCING TO OUR NORTH INTO ONTARIO AND THE NORTHEAST. CONTINUED  
WITH A HIGHLY BLENDED APPROACH FOR MUCH OF NEXT WEEK GIVEN THESE  
TIMING DIFFERENCES. HIGHS IN THE UPPER 70S TUESDAY, DROPPING  
INTO THE 60S BEHIND THE COLD FRONT WEDNESDAY.  
 

 
   
AVIATION /02Z THURSDAY THROUGH MONDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
THROUGH TONIGHT...VFR. WEST 5-10 KNOTS THIS EVENING BECOME LIGHT  
AND VARIABLE/CALM THROUGH THE EVENING AND OVERNIGHT HOURS. HIGH  
CONFIDENCE.  
 
THERE IS A CHANCE FOR PATCHY FOG LATER TONIGHT, MAINLY JUST  
RADIATION INDUCED GROUND FOG, SO VISIBILITIES ARE NOT EXPECTED  
TO DROP SIGNIFICANTLY AT THIS TIME AT THE TAF SITES.  
 
THURSDAY AND THURSDAY NIGHT...VFR. LIGHT AND VARIABLE WINDS  
EARLY THURSDAY, BECOME WEST TO SOUTHWEST 5-10 KNOTS THROUGH THE  
MORNING INTO THE AFTERNOON BEFORE DIMINISHING THURSDAY EVENING. HIGH  
CONFIDENCE.  
 
OUTLOOK...  
 
FRIDAY AND SATURDAY...SUB-VFR CONDITIONS POSSIBLE AT TIMES WITH  
RAIN SHOWERS AS THE REMNANTS OF BETA MOVE TO OUR SOUTH.  
QUESTIONS REMAIN AS TO HOW FAR NORTH PRECIPITATION WILL REACH,  
WITH BEST CHANCES SOUTH OF THE PHILLY TERMINALS. SOUTHERLY WINDS  
FROM 5 TO 10 KNOTS. MODERATE CONFIDENCE.  
 
SUNDAY AND MONDAY...VFR CONDITIONS SUNDAY AND FOR MUCH OF THE  
DAY MONDAY BEFORE SHOWERS MOVE INTO THE REGION MONDAY PM.  
SOUTHWESTERLY WINDS FROM 10 TO 15 KNOTS. MODERATE CONFIDENCE.  
 

 
   
MARINE
 
 
NOW THAT ALL ADVISORIES HAVE BEEN CANCELLED, ALL MARINE ZONES  
ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS THROUGH THURSDAY  
NIGHT, ALTHOUGH WINDS COULD GUST AROUND 20 KNOTS AT TIMES.  
 
OUTLOOK...  
 
THURSDAY THROUGH MONDAY...SUB-ADVISORY WINDS/SEAS EXPECTED WITH  
PREDOMINANTLY SOUTHWESTERLY FLOW FROM 10 TO 15 KNOTS. PERIODIC  
CHANCES FOR SHOWERS FRIDAY AND MONDAY.  
 
RIP CURRENTS...  
 
AS SEAS SUBSIDE TO 2-3 FEET WITH A 10 SECOND SWELL ON THURSDAY,  
WE EXPECT THE RIP- CURRENT RISK WILL LOWER TO THE MODERATE  
CATEGORY.  
 
THE RISK MAY END UP BEING LOW ON FRIDAY AS SWELLS DECREASE EVEN  
FURTHER.  
 

 
   
TIDES/COASTAL FLOODING
 
 
A FINAL SURGE FROM TROPICAL SYSTEM TEDDY ARRIVED ALONG THE  
COASTS OF NEW JERSEY AND DELAWARE TODAY, RESULTING IN ONE FINAL  
ROUND OF MINOR TIDAL FLOODING. TIDAL DEPARTURES WILL CONTINUE  
TO DECREASE OVER THE COMING DAYS AND NO ADDITIONAL FLOODING IS  
EXPECTED.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...NONE.  
 

 
 

 
 
SYNOPSIS...DAVIS  
NEAR TERM...FITZSIMMONS/ROBERTSON  
SHORT TERM...FITZSIMMONS  
LONG TERM...DAVIS  
AVIATION...DAVIS/FITZSIMMONS/ROBERTSON  
MARINE...DAVIS/FITZSIMMONS/ROBERTSON  
TIDES/COASTAL FLOODING...IOVINO  
 
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