664  
FXUS61 KPHI 242344  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
744 PM EDT SUN MAY 24 2020  
   
SYNOPSIS
 
 
HIGH PRESSURE STRETCHED ACROSS OUR REGION FROM THE NORTHEAST THIS  
AFTERNOON WILL GRADUALLY WEAKEN SOME AND SHIFT EASTWARD THROUGH  
EARLY THIS WEEK, THEN IT REMAINS ANCHORED OFFSHORE THROUGH LATE THIS  
WEEK. A COLD FRONT CROSSES OUR REGION LATER FRIDAY INTO SATURDAY,  
THEN HIGH PRESSURE BUILDS IN FOR SUNDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM MONDAY MORNING/
 
 
THE ONSHORE FLOW ACROSS THE REGION CONTINUES THIS EVENING. NOW  
THAT THE DAYTIME MIXING HAS ENDED, AN OVERALL INCREASE IN CLOUD  
COVER AND PERHAPS SOME DRIZZLE NEAR THE SHORE IS EXPECTED OVERNIGHT.  
SOME BREAKS IN THE CLOUDS COULD ALSO LEAD TO SOME FOG FORMATION,  
BUT IT IS NOT EXPECTED TO BE DENSE. THESE BREAKS WILL LIKELY BE  
MORE COMMON ACROSS THE FAR N OR NW AREAS.  
 
FEW CHANGES WERE MADE TO TEMPS, DEW POINT GRIDS OR WINDS. THE LOWS  
TONIGHT WILL BE IN THE LOW TO MID 50S FOR THE MOST PART.  
 

 
   
SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/
 
 
MONDAY IS EXPECTED TO BEGIN UNDER AN OVERCAST SKY IN NORTHEASTERN  
MARYLAND AND DELAWARE, AND IN MUCH OF NEW JERSEY AND EASTERN  
PENNSYLVANIA. AS THE SURFACE RIDGE RETREATS A BIT, THE FLOW SHOULD  
VEER TOWARD THE SOUTHEAST.  
 
THE STRONG LATE MAY SUNSHINE IS FORECAST TO PRODUCE ENOUGH MIXING ON  
MONDAY TO CAUSE THE CLOUDS TO LIFT AND BREAK OVER MUCH OF OUR REGION  
FOR THE AFTERNOON HOURS. HIGH TEMPERATURES ARE EXPECTED TO BE MOSTLY  
IN THE 70S, WITH READINGS NOT GETTING ABOVE THE 60S NEAR THE COAST.  
 

 
   
LONG TERM /MONDAY NIGHT THROUGH SUNDAY/
 
 
SUMMARY...A MUCH WARMER AIRMASS (AND MORE HUMID) SURGES INTO THE  
REGION THIS WEEK, FOLLOWED BY A LITTLE COOLING OVER THE WEEKEND.  
SHOWER AND THUNDERSTORM CHANCES INCREASE MOSTLY FOR FRIDAY.  
 
SYNOPTIC OVERVIEW...AN UPPER-LEVEL RIDGE IS FORECAST TO BUILD ACROSS  
THE EAST THROUGH TUESDAY BEFORE SHIFTING MORE OFFSHORE. AT THE  
SURFACE, HIGH PRESSURE INITIALLY CENTERED JUST SOUTH OF THE CANADIAN  
MARITIMES EXTENDS WEST AND SOUTHWEST INTO THE MID-ATLANTIC, THEN IT  
BECOMES MORE CENTERED INTO THE WESTERN ATLANTIC AS THE  
AFOREMENTIONED RIDGE SHIFTS EASTWARD. AN UPPER-LEVEL TROUGH SLIDING  
ACROSS SOUTHERN CANADA IS FORECAST TO AMPLIFY SOME INTO THE GREAT  
LAKES AND NEW ENGLAND LATE IN THE WEEK. AN ATTENDANT SURFACE LOW  
TRACKS WELL TO OUR NORTH, HOWEVER ITS COLD FRONT MOVES THROUGH LATER  
FRIDAY INTO SATURDAY. THE TROUGH SHOULD THEN AMPLIFY MORE INTO THE  
EAST SUNDAY WITH SURFACE HIGH PRESSURE BUILDING IT.  
 
FOR MONDAY NIGHT AND TUESDAY...A RIDGE ALOFT BUILDS ACROSS THE  
REGION WITH SURFACE HIGH PRESSURE BECOMING ANCHORED MORE OFFSHORE  
AND TO OUR EAST. THIS WILL RESULT IN THE LOW-LEVEL FLOW BEING  
SOUTHERLY ALONG WITH WARM AIR ADVECTION OCCURRING. GIVEN THE  
PRESENCE OF THE RIDGE, NO PRECIPITATION IS EXPECTED. HOWEVER, THE  
LOW-LEVEL MOISTURE WILL CONTINUE TO INCREASE AND WITH A SUBSIDENCE  
INVERSION IN PLACE DESPITE A MORE SOUTHERLY FLOW, AREAS OF LOW  
CLOUDS SHOULD DEVELOP ONCE AGAIN DURING THE NIGHT AND A PORTION OF  
TUESDAY MORNING. SOME FOG IS ANTICIPATED AS WELL. ONCE THESE  
DISSIPATE DURING TUESDAY MORNING, TEMPERATURES SHOULD BE OFF TO THE  
RACES AS AMPLE BOUNDARY LAYER WARMING OCCURS WITH AFTERNOON  
TEMPERATURES INTO THE 80S FOR MANY PLACES. THE EXCEPTION ARE THE  
SOUTHEAST OR SOUTH FACING BEACHES INITIALLY WHICH WILL HAVE A MORE  
ONSHORE WIND COMPONENT AND THEREFORE COOLER TEMPERATURES. THE LOW-  
LEVEL FLOW IS NOT FORECAST TO BE ALL THAT STRONG, THEREFORE A  
SEA/BAY BREEZE IS ANTICIPATED TO DEVELOP DURING TUESDAY AS THE  
LAND/WATER TEMPERATURE DIFFERENTIAL INCREASES QUITE A BIT  
(INCREASING THE ONSHORE FLOW COMPONENT ALL ALONG THE COAST).  
 
FOR WEDNESDAY AND THURSDAY...WHILE AN UPPER-LEVEL RIDGE SHIFTS MORE  
OFFSHORE IT STILL REMAINS OVER OUR REGION WEDNESDAY BEFORE WEAKENING  
A LITTLE THURSDAY. SURFACE HIGH PRESSURE WILL REMAIN ANCHORED WELL  
OFFSHORE, RESULTING IN A CONTINUED SOUTHERLY FLOW OF WARMER AND MORE  
HUMID AIR. WHILE MUCH OF THIS TIME FRAME MAY END UP BEING DRY, THERE  
LOOKS TO BE SOME OPPORTUNITY FOR SOME CONVECTION AROUND THE WESTERN  
FLANK OF THE RIDGE. THIS SHOULD BE MORESO DURING THURSDAY AS AN  
UPPER-LEVEL TROUGH IN EASTERN CANADA STARTS TO GLANCE OUR REGION.  
THERE MAY BE JUST ENOUGH COOLING ALOFT ALONG WITH PERHAPS A LEE-SIDE  
TROUGH AND TERRAIN CIRCULATIONS TO DEVELOP MOSTLY SOME DIURNALLY  
DRIVEN CONVECTION, ESPECIALLY IN THE WESTERN PART OF THE AREA. A SEA  
BREEZE EACH DAY (ESPECIALLY WEDNESDAY) SHOULD RESULT IN COOLING  
ALONG THE COAST.  
 
FOR FRIDAY AND SATURDAY...THE SOUTHERN PORTION OF THE UPPER-LEVEL  
TROUGH ACROSS EASTERN CANADA WILL SWING ACROSS THE NORTHEAST FRIDAY  
WITH A MORE NOTABLE AMPLIFICATION DURING SATURDAY. AT THE SURFACE,  
LOW PRESSURE TRACKS WELL TO OUR NORTH PULLING A COLD FRONT ACROSS  
OUR AREA LATER FRIDAY INTO SATURDAY. WHILE THE TIMING OF THE FRONTAL  
PASSAGE VARIES TO A DEGREE, SOME SHOWERS AND THUNDERSTORMS ARE  
PROBABLE ALONG AND AHEAD OF THE FRONT. THE STRONGER FLOW MAY RESIDE  
FARTHER NORTH AND DISPLACED FROM THE GREATER INSTABILITY FRIDAY,  
THEREFORE THE INTENSITY OF ANY THUNDERSTORMS IS LESS CERTAIN. THE  
COLD FRONT SHOULD BE CLEARING MUCH OF OUR AREA TO START SATURDAY  
MORNING, THEREFORE SOME DRIER AIR WILL BE WORKING IN. BASED ON THIS  
AND THE ARRIVAL OF THE MAIN TROUGH ALOFT, INSTABILITY SHOULD BE ON  
THE WAY DOWN HOWEVER DID HANG ONTO SOME SLIGHT CHANCE OR LOW CHANCE  
POPS SATURDAY FOR A TIME.  
 
FOR SUNDAY...THE UPPER-LEVEL TROUGH IS FORECAST TO DOMINATE THE EAST  
WITH SURFACE HIGH PRESSURE BUILDING IN. THIS WILL RESULT IN DRY  
CONDITIONS AND ALSO SOME COOLER TEMPERATURES. THE SURFACE WINDS MAY  
ONCE AGAIN TURN ONSHORE AND THEREFORE EVEN COOLER TEMPERATURES FOR  
THE COASTAL COMMUNITIES.  
 

 
   
AVIATION /00Z MONDAY THROUGH FRIDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TONIGHT...VFR AND MVFR CEILINGS THIS EVENING, WITH CONDITIONS  
LOWERING TO IFR OVERNIGHT. A LITTLE DRIZZLE POSSIBLE NEAR KACY.  
PATCHY FOG POSSIBLE. NORTHEAST TO EAST WIND 4 TO 8 KNOTS.  
MEDIUM TO HIGH CONFIDENCE.  
 
MONDAY...IFR CONDITIONS IMPROVING TO MVFR IN THE MORNING, THEN TO  
VFR FOR THE AFTERNOON WITH A DECREASE IN CLOUD COVER AT THAT TIME.  
EAST TO SOUTHEAST WIND 5 TO 10 KNOTS. MEDIUM TO HIGH CONFIDENCE.  
 
OUTLOOK...  
MONDAY NIGHT AND TUESDAY...MVFR TO IFR CEILINGS DEVELOP THEN IMPROVE  
BACK TO VFR DURING TUESDAY. SOME LOCAL FOG POSSIBLE TUESDAY MORNING.  
EAST-SOUTHEAST WINDS LESS THAN 10 KNOTS. LOW CONFIDENCE WITH TIMING  
OF FLIGHT CATEGORY CHANGES.  
 
WEDNESDAY...AREAS OF MVFR CEILINGS POSSIBLE TO START, OTHERWISE VFR.  
SOUTHERLY WINDS 5-10 KNOTS, BECOMING LIGHT AND VARIABLE AT NIGHT.  
MODERATE CONFIDENCE.  
 
THURSDAY...MAINLY VFR. SOME SHOWERS AND THUNDERSTORMS POSSIBLE IN  
THE AFTERNOON AND EVENING ESPECIALLY WEST OF PHL. SOUTH WINDS AROUND  
10 KNOTS. LOW CONFIDENCE ON TIMING OF ANY THUNDERSTORMS.  
 
FRIDAY...TIMES OF SUB-VFR CONDITIONS PROBABLE AS SHOWERS AND  
THUNDERSTORMS INCREASE DURING THE DAY. SOUTHWEST WINDS 10-15 KNOTS,  
BECOMING WEST TO NORTHWEST AT NIGHT AND DIMINISHING. LOW  
CONFIDENCE.  
 

 
   
MARINE
 
 
A SMALL CRAFT ADVISORY IS IN EFFECT FOR TONIGHT AND MONDAY MORNING  
ON OUR OCEAN WATERS.  
 
A NORTHEAST WIND 10 TO 15 KNOTS THROUGH MONDAY MORNING IS EXPECTED  
TO DIMINISH TO 5 TO 10 KNOTS ON MONDAY AFTERNOON AS THE DIRECTION  
BEGINS TO VEER TOWARD THE EAST.  
 
WAVE HEIGHTS ON OUR OCEAN WATERS SHOULD REMAIN AROUND 5 TO 6 FEET  
INTO MONDAY MORNING, BEFORE SUBSIDING TO AROUND 4 FEET IN THE  
AFTERNOON.  
 
OUTLOOK...  
MONDAY NIGHT THROUGH WEDNESDAY...THE CONDITIONS ARE ANTICIPATED TO  
BE BELOW SMALL CRAFT ADVISORY CRITERIA. SOME FOG POSSIBLE LATER  
MONDAY NIGHT AND TUESDAY MORNING.  
 
THURSDAY AND FRIDAY...SOUTH TO SOUTHWEST WINDS INCREASE WITH GUSTS  
APPROACHING 25 KNOTS. HOWEVER, MUCH WARMER AIR WILL BE MOVING OVER  
THE COOLER WATERS AND THEREFORE THE AMOUNT OF MIXING IS IN QUESTION.  
THE WINDS SHOULD SHIFT TO WEST AND NORTHWEST FRIDAY NIGHT. SHOWER  
AND THUNDERSTORM CHANCES INCREASE ON FRIDAY.  
 
RIP CURRENTS...  
A PREVAILING MEDIUM PERIOD NORTHEASTERLY SWELL WILL MAINTAIN A  
MODERATE RISK FOR THE DEVELOPMENT OF DANGEROUS RIP CURRENTS INTO  
MONDAY.  
 

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

 
 

 
SYNOPSIS...GORSE  
NEAR TERM...O'HARA  
SHORT TERM...IOVINO  
LONG TERM...GORSE  
AVIATION...GORSE/IOVINO/PO  
MARINE...GORSE/IOVINO  
 
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