337  
FXUS61 KPHI 130038  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
838 PM EDT MON APR 12 2021  
   
SYNOPSIS
 
 
LOW PRESSURE LOCATED OFF THE MIDDLE ATLANTIC COAST THIS  
AFTERNOON WILL CONTINUE TO DRIFT FARTHER OUT TO SEA. WEAK HIGH  
PRESSURE IS FORECAST TO INFLUENCE OUR WEATHER ON TUESDAY.  
ANOTHER AREA OF LOW PRESSURE IS EXPECTED TO DEVELOP IN NORTH  
CAROLINA ON WEDNESDAY BEFORE PASSING OFF THE VIRGINIA COAST ON  
WEDNESDAY NIGHT. THE SYSTEM IS ANTICIPATED TO MOVE SLOWLY  
NORTHEASTWARD ON THURSDAY AND FRIDAY. HIGH PRESSURE IS EXPECTED  
TO BUILD INTO OUR REGION FROM THE NORTHWEST AND NORTH DURING THE  
WEEKEND. WEAK LOW PRESSURE OR A COLD FRONT MAY FOLLOW FOR  
SUNDAY NIGHT INTO MONDAY.  
 

 
   
NEAR TERM /THROUGH TUESDAY/
 
 
THE BROAD SCALE BLOCKING PATTERN CONTINUES ACROSS THE CONUS  
THROUGH TUESDAY. A CLOSED UPPER LOW LOCATED TO OUR NORTHWEST IS  
EXPECTED TO OPEN AND EJECT EASTWARD ACROSS THE MID-ATLANTIC  
TONIGHT WITH A LARGER AND STRONGER CLOSED UPPER LOW MOVING FROM  
THE NORTHERN PLAINS TOWARD THE GREAT LAKES DURING THE DAY  
TUESDAY. AT THE SURFACE, A BROAD AND STRUNG OUT AREA OF LOW  
PRESSURE EXTENDS FROM THE GREAT LAKES REGION AND TO THE  
SOUTHEAST ACROSS THE WESTERN ATLANTIC. HIGH PRESSURE CENTERED  
WELL NORTHEAST OF THE REGION CONTINUES TO RIDGE DOWN INTO OUR  
AREA.  
 
THE SURFACE RIDGING WILL CONTINUE FEEDING IN THE COOL AND DAMP  
AIR WE'VE HAD IN PLACE FOR THE PAST 24 HOURS OR SO, AND AS SUCH  
TEMPERATURES ARE FORECAST TO REMAIN LARGELY STEADY IN THE 40S  
THROUGH THE OVERNIGHT PERIOD. A NOTABLE NORTHEASTERLY BREEZE  
WILL PERSIST AS WELL UNDER THE LOW STRATUS DECK. AS THE UPPER  
LOW EJECTS OVER THE REGION TONIGHT, ANOTHER ROUND OF  
SHOWERS/DRIZZLE IS FORECAST OVERNIGHT ACROSS MUCH OF THE AREA,  
MAINLY BETWEEN ABOUT MIDNIGHT AND 6 AM.  
 
AS THE OPENING UPPER LOW DEPARTS TUESDAY MORNING ALONG WITH THE  
REGRESSION OF THE SURFACE RIDGING, WE SHOULD SEE CONSIDERABLE  
CLEARING DURING THE MORNING HOURS FROM EAST TO WEST.  
TEMPERATURES WILL ALSO RISE TO NEAR NORMAL VALUES, WITH FORECAST  
HIGHS IN THE LOW TO MID 60S AWAY FROM THE COASTS. EXPECT  
NORTHERLY WINDS AROUND 5-10 MPH DURING THE DAY AS WELL.  
 

 
   
SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/
 
 
THE AXIS OF A MID LEVEL RIDGE IS FORECAST TO PASS OVERHEAD ON  
TUESDAY NIGHT, BEFORE DRIFTING TO OUR EAST ON WEDNESDAY. WE ARE  
ANTICIPATING AN INCREASE IN CLOUD COVER ON TUESDAY NIGHT WITH  
LIGHT RAIN ARRIVING FROM THE WEST ON WEDNESDAY, AHEAD OF OUR  
NEXT WEATHER SYSTEM.  
 
A SHORT WAVE TROUGH TRAVELING IN THE WESTERLY MID LEVEL FLOW IS  
EXPECTED TO PASS OVER THE SOUTHEASTERN STATES ON WEDNESDAY AND  
WEDNESDAY EVENING. A SURFACE LOW IS FORECAST TO DEVELOP IN NORTH  
CAROLINA ON WEDNESDAY BEFORE MOVING OFF THE VIRGINIA COAST ON  
WEDNESDAY NIGHT. THE LOW SHOULD THEN DRIFT NORTHEASTWARD OVER  
THE WATERS OFF MARYLAND, DELAWARE AND SOUTHERN NEW JERSEY ON  
THURSDAY.  
 
WE ARE EXPECTING AN INCREASING CHANCE OF RAIN FROM WEDNESDAY  
NIGHT INTO THURSDAY. WHILE SOME MODERATE TO HEAVY RAIN IS  
POSSIBLE IN SPOTS, IT IS DIFFICULT TO PINPOINT EXACTLY WHICH  
AREAS ARE MOST LIKELY TO RECEIVE IT. THE SAME IS TRUE WITH THE  
POTENTIAL FOR LOCALIZED THUNDER.  
 
A LIGHT SOUTHWEST WIND ON WEDNESDAY IS FORECAST TO BECOME EAST  
TO NORTH GENERALLY AROUND 10 TO 15 MPH ON THURSDAY AS THE LOW  
DRIFTS OUT TO SEA. HIGHS ARE EXPECTED TO FAVOR THE 60S ON  
WEDNESDAY, AND THE 50S ON THURSDAY DUE TO THE CHILLY ONSHORE  
FLOW.  
 

 
   
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
 
 
A MID LEVEL LOW APPROACHING SLOWLY FROM THE GREAT LAKES IS  
EXPECTED TO PASS OVERHEAD FROM LATE THURSDAY NIGHT INTO FRIDAY  
MORNING. THE FEATURE WILL CONTINUE TO BRING A CHANCE OF SHOWERS  
TO OUR REGION. THERE MAY BE ENOUGH COLD AIR IN THE ELEVATED  
TERRAIN OF THE POCONOS TO RESULT IN SOME LATE SEASON SNOW FLAKES  
AT THAT TIME.  
 
THE MID LEVEL LOW IS ANTICIPATED TO MOVE OUT TO SEA OVER THE  
WEEKEND. DRY AIR IS FORECAST TO BUILD INTO OUR REGION FROM THE  
NORTHWEST AND NORTH FOR FRIDAY NIGHT AND SATURDAY.  
 
THE SURFACE HIGH SHOULD PASS OFF THE COAST AND BEGIN TO MOVE  
OUT OVER THE WESTERN NORTH ATLANTIC ON SUNDAY. WE MAY SEE SOME  
SHOWERS IN THE RETURN FLOW ON THE BACK SIDE OF THE HIGH ON  
SUNDAY AFTERNOON. A MID LEVEL TROUGH IS EXPECTED TO APPROACH  
FROM THE WEST ON SUNDAY NIGHT AND MONDAY.  
 
TEMPERATURES WILL LIKELY REMAIN BELOW NORMAL FOR FRIDAY DUE TO  
THE MID LEVEL LOW. READINGS ARE FORECAST TO RETURN NEAR NORMAL  
FOR THE WEEKEND AND FOR MONDAY.  
 

 
   
AVIATION /01Z TUESDAY THROUGH SATURDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TONIGHT...INITIALLY MVFR, WITH IFR CEILINGS DEVELOPING AFTER  
ABOUT 02-03Z. THERE IS SOME POSSIBILITY THAT THE WESTERN SITES  
WILL STAY MVFR BUT CONFIDENCE IN THIS IS LOW. SOME COMBINATION  
OF LIGHT RAIN SHOWERS AND/OR DRIZZLE/MIST WILL BE POSSIBLE IN  
THE 03-09Z TIME FRAME. THE IFR CEILINGS SHOULD BECOME MVFR  
AROUND 09Z. WINDS NORTHEASTERLY AROUND 5 KTS. MODERATE  
CONFIDENCE.  
 
TUESDAY...INITIALLY MVFR CEILINGS SHOULD SCATTER OUT IN THE  
14-16Z TIME FRAME WITH VFR CONDITIONS THEN PREVAILING THE  
REMAINDER OF THE DAY. INITIALLY NORTHEASTERLY WINDS AROUND 5-10  
KTS WILL BECOME MORE NORTHERLY 5-10KTS AFTER 15Z. MODERATE  
CONFIDENCE.  
 
OUTLOOK...  
 
WEDNESDAY...MAINLY VFR. A CHANCE OF SHOWERS IN THE AFTERNOON.  
SOUTHWEST WIND 5 TO 10 KNOTS. MEDIUM TO HIGH CONFIDENCE.  
 
THURSDAY...IFR/MVFR WITH RAIN LIKELY. EAST TO NORTH WIND  
INCREASING TO 10 TO 15 KNOTS WITH GUSTS AROUND 20 KNOTS. MEDIUM  
CONFIDENCE.  
 
FRIDAY...MVFR/VFR WITH A CHANCE OF SHOWERS. NORTHWEST WIND 10  
TO 15 KNOTS WITH GUSTS OF 20 TO 25 KNOTS. MEDIUM CONFIDENCE.  
 
SATURDAY...MAINLY VFR. NORTHWEST WIND 10 TO 15 KNOTS. MEDIUM  
CONFIDENCE.  
 

 
   
MARINE
 
 
A SMALL CRAFT ADVISORY WILL REMAIN IN EFFECT THROUGH TONIGHT  
AND THROUGH MUCH OF TUESDAY MORNING ACROSS THE OCEAN WATERS.  
SEAS OF 3-6 FEET AREA FORECAST TONIGHT, WHICH WILL GRADUALLY  
SUBSIDE TOMORROW MORNING TO BELOW 5 FEET INTO THE AFTERNOON.  
WINDS NORTHEASTERLY AROUND 15-20 KTS WITH GUSTS UP TO 25 KTS  
ACROSS THE OCEAN WATERS. THE WINDS WILL ALSO GRADUALLY DIMINISH  
THROUGHOUT THE DAY TUESDAY AS WELL AND BECOME MORE NORTHERLY.  
 
OUTLOOK...  
 
WEDNESDAY...NO MARINE HEADLINES ARE ANTICIPATED.  
 
THURSDAY...EAST TO NORTH WIND INCREASING TO 15 TO 20 KNOTS WITH  
GUSTS AROUND 25 KNOTS.  
 
FRIDAY...NORTHWEST WIND 15 TO 20 KNOTS WITH GUSTS OF 25 TO 30  
KNOTS.  
 
SATURDAY...NO MARINE HEADLINES ARE ANTICIPATED.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EDT TUESDAY FOR ANZ451>455.  
SMALL CRAFT ADVISORY UNTIL 11 AM EDT TUESDAY FOR ANZ450.  
 

 
 

 
SYNOPSIS...IOVINO  
NEAR TERM...STAARMANN  
SHORT TERM...IOVINO  
LONG TERM...IOVINO  
AVIATION...CARR/IOVINO/STAARMANN  
MARINE...IOVINO/STAARMANN  
 
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