261  
FXUS61 KPHI 232032  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
432 PM EDT SUN JUL 23 2017  
   
SYNOPSIS
 
 
A FRONTAL BOUNDARY EXTENDED FROM THE SOUTHERN GREAT LAKES TO  
OUR REGION THIS AFTERNOON. LOW PRESSURE WILL RIDE EASTWARD ALONG  
THE FRONT AND IT SHOULD PASS THROUGH OUR AREA ON MONDAY. A  
SECOND LOW WILL FOLLOW ON MONDAY NIGHT AND TUESDAY AS THE  
BOUNDARY SINKS SLOWLY TO THE SOUTH. HIGH PRESSURE IS FORECAST TO  
BUILD DOWN FROM THE NORTHWEST FOR THE MIDDLE PART OF THE WEEK.  
A COLD FRONT FROM THE NORTHWEST IS ANTICIPATED TO ARRIVE ON  
FRIDAY. THE FRONT IS EXPECTED TO MOVE SLOWLY TO OUR SOUTHEAST  
OVER THE WEEKEND AS AREAS OF LOW PRESSURE TRAVEL ALONG IT.  
 

 
   
NEAR TERM /UNTIL 6 AM MONDAY MORNING/
 
 
**A FLASH FLOOD WATCH IS IN EFFECT FOR THE I-95 CORRIDOR AND  
AREAS TO THE NORTH AND WEST FOR TONIGHT THROUGH EARLY MONDAY  
MORNING.**  
 
A NICE BREAK FROM THE HEAT OF THE PAST COUPLE DAYS TODAY AS A  
BOUNDARY SANK SOUTHWARD THROUGH THE REGION, BRINGING IN A COOLER  
EASTERLY FLOW. AREAS ALONG DELMARVA REMAINED BELOW THE BOUNDARY  
AND REMAINED A BIT WARMER (AND MOISTER) WITH A SOUTHWESTERLY  
FLOW ALL DAY.  
 
CONVECTION HAS STARTED FIRING UP THIS AFTERNOON, MAINLY IN THE  
VICINITY OF THE (ESSENTIALLY) STALLED BOUNDARY. THIS WILL BE THE  
MAIN FOCUS AREA, ESPECIALLY THIS AFTERNOON AND EARLY EVENING,  
FOR CONVECTION TO DEVELOP AND SUSTAIN ITSELF. CONVECTION WILL  
REMAIN SCATTERED ACROSS THE AREA THROUGH THIS EVENING. THIS  
FIRST ROUND WILL LOSE SOME OF ITS OOMPH AS THE SUN SETS AND IT  
LOSES SOME OF THE MUCH NEEDED LIFT IT NEEDS TO BE SUSTAINED.  
AREAS TO THE NORTH AND EAST OF THE BOUNDARY ARE LITTLE MORE  
STABLE DUE TO THE CONTINUED ONSHORE FLOW AND WILL SEE LESS  
ACTIVITY (IF ANY) THIS AFTERNOON AND EARLY EVENING.  
 
THE BOUNDARY MAY MOVE SLIGHTLY NORTH TONIGHT BUT WILL REMAIN  
NEARLY STATIONARY INTO MONDAY. A LOW PRESSURE SYSTEM WILL  
DEVELOP ALONG THE BOUNDARY AND MOVE INTO OUR AREA LATE TONIGHT.  
HEAVY RAIN AND THUNDERSTORMS WILL ACCOMPANY THE SYSTEM. THIS  
SECOND BATCH OF RAIN IS MORE PROBLEMATIC THAN THE CONVECTION WE  
WILL SEE THIS AFTERNOON AND EVENING. A GOOD SWATCH OF 1-2 INCHES  
OF RAIN FELL LAST NIGHT. WE HAVE NOT HAD AMPLE TIME TO DRY OUT  
SO THE GROUND WILL BE UNABLE TO ABSORB NEARLY AS MUCH  
PRECIPITATION AS IT OTHERWISE WOULD. MODELS HAVE TRENDED WETTER  
WITH THE LATEST RUNS AND PUT A BULLSEYE, OR MORE OF A HEAVY  
SWATH, OF RAIN ACROSS OUR AREA. THE FOCUS LOOKS TO BE MORE ALONG  
THE I-95 CORRIDOR BUT SOME OF THE MODELS SHOW A SLIGHT SHIFT TO  
THE NORTH AND WEST OF I-95. WITH PWATS STILL RUNNING AROUND  
1.5-2.0 INCHES ACROSS THE REGION, WE WILL HAVE PLENTY OF  
MOISTURE TO FEED INTO SHOWERS AND THUNDERSTORMS AND TORRENTIAL  
RAINFALL WILL OCCUR. WHILE THE MODELS ARE OUTPUTTING PRETTY  
HIGH, AND WHAT LOOK LIKE UNREASONABLE, AMOUNTS IT SEEMS LIKELY  
THAT A GOOD 2-4 INCH RAINFALL WILL OCCUR WITHIN OUR CWA. A LACK  
OF STRONG FLOW AT THE SURFACE AND ALOFT SHOWS THAT STORMS MAY  
NOT MOVE VERY QUICKLY (OR AT ALL), ENHANCING THE FLASH FLOOD  
THREAT.  
 
WITH HIGHER CONFIDENCE THAT FLASH FLOODING WILL OCCUR SOMEWHERE  
IN THE CWA, WE HAVE ISSUED A FLASH FLOOD WATCH FOR THE I-95  
CORRIDOR AND AREAS TO THE NORTH AND WEST THROUGH MONDAY MORNING.  
 
TEMPERATURES HAVE CERTAINLY BEEN COOLER TODAY THAN OF LATE BUT  
EXPECT A DECENT AMOUNT OF CLOUD COVER TO REMAIN OVER THE REGION  
THROUGH TONIGHT. THIS WILL KEEP THE TEMPERATURES MORE MODERATE  
OVERNIGHT TONIGHT. EXPECT LOWS TO RANGE FROM THE UPPER 60S  
ACROSS THE SOUTHERN POCONOS TO THE LOW TO MID 70S ACROSS THE  
REGION.  
 

 
   
SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/
 
 
THE BOUNDARY REMAINS IN THE AREA WITH THE LOW PRESSURE SYSTEM  
MOVING THROUGH THE REGION ON MONDAY. A COLD FRONT WILL DROP DOWN  
FROM THE THE NORTH ON MONDAY, TAKING ITS TIME AS IT MAKES ITS  
WAY THROUGH OUR AREA. A CONTINUED CHANCE FOR SHOWERS EXISTS  
THROUGH MUCH OF THE DAY WITH A CHANCE FOR SOME THUNDERSTORMS AS  
WELL. HEAVY RAIN WILL REMAIN A THREAT IN SOME OF THE STRONGER  
SHOWERS AND IN THUNDERSTORMS.  
 
SOME CLEARING MAY OCCUR DURING THE AFTERNOON, MAINLY SOUTHERN  
AREAS, WITH MORE CLEARING EXPECTED TOWARDS EVENING.  
 
HIGHS WILL REBOUND SLIGHTLY AND DEWPOINTS SHOULD START TO DROP,  
ALTHOUGH THAT MAY BE A SLOWER PROCESS. IT WILL STILL FEEL  
HUMID, ESPECIALLY ACROSS DELMARVA AND EXTREME SOUTHERN NEW  
JERSEY. EXPECT HIGHS TO BE IN THE LOWER 90S FROM  
I-95/PHILADELPHIA AND POINTS TO THE SOUTH AND IN THE MID TO  
UPPER 80S THROUGH CENTRAL NEW JERSEY. LEHIGH VALLEY, POCONO AND  
NORTHERN NEW JERSEY WILL REMAIN COOLER WITH HIGHS IN THE 70S TO  
AROUND 80.  
 

 
   
LONG TERM /MONDAY NIGHT THROUGH SUNDAY/
 
 
A CHANCE OF SHOWERS AND THUNDERSTORMS WILL LINGER INTO MONDAY  
NIGHT. BASED ON THE LATEST MODEL GUIDANCE, DRYING MAY BE DELAYED  
A BIT. IT NOW APPEARS AS THOUGH THE MID LEVEL SHORT WAVE TROUGH  
FROM THE NORTHWEST WILL NOT ARRIVE UNTIL LATE TUESDAY. AS A  
RESULT, WE WILL KEEP SOME CLOUDS AND A SLIGHT CHANCE OF SHOWERS  
FOR TUESDAY.  
 
DRY AIR IS ANTICIPATED TO FOLLOW THE MID LEVEL TROUGH FOR  
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT.  
 
A COLD FRONT IS EXPECTED TO APPROACH FROM THE NORTHWEST ON  
THURSDAY AND IT SHOULD PASS THROUGH OUR REGION ON FRIDAY. WE  
WILL INDICATE AN INCREASING CHANCE FOR SHOWERS AND THUNDERSTORMS  
AT THAT TIME.  
 
THE FORWARD PROGRESS OF THE FRONT IS EXPECTED TO SLOW OVER THE  
WEEKEND AS WAVES OF LOW PRESSURE TRAVEL ALONG THE BOUNDARY. WE  
WILL CONTINUE TO CARRY A MAINLY DRY FORECAST FOR SATURDAY AND  
SUNDAY, BUT THAT COULD CHANGE IF THE FRONT STARTS TO TREND  
TOWARD BEING EVEN LESS PROGRESSIVE.  
 
TEMPERATURES ARE EXPECTED TO BE SEASONABLE DURING THE PERIOD  
FROM MONDAY NIGHT THROUGH SUNDAY.  
 

 
   
AVIATION /21Z SUNDAY THROUGH FRIDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
SCATTERED CONVECTION ACROSS THE REGION THROUGH TONIGHT WITH  
SHOWERS CONTINUING THROUGH THE OVERNIGHT HOURS. PERIODS OF HEAVY  
RAIN WITH IFR CONDITIONS POSSIBLE, ESPECIALLY FROM KILG/KPHL  
AND TERMINALS TO THE NORTH AND WEST. TIMING REMAINS AN ISSUE BUT  
BEST TIME FRAME FOR CONVECTION THIS EVENING IS BETWEEN 23Z-04Z  
WITH LOWER CONFIDENCE IN CONVECTION OVERNIGHT. THERE REMAINS THE  
POTENTIAL FOR STRONG TO SEVERE STORMS TODAY WITH GUSTY TO  
DAMAGING DOWNBURST WINDS AND TORRENTIAL RAINFALL.  
 
VFR/MVFR CONDITIONS HAVE PREVAILED THROUGH MUCH OF THE DAY AND  
WE SHOULD SEE MAINLY VFR CONDITIONS AT THE TERMINALS OUTSIDE OF  
SHOWERS AND CONVECTION. CONDITIONS WILL DETERIORATE AS STORMS  
ARRIVE AND CEILINGS AND VISIBILITIES WILL REMAIN MVFR, POSSIBLY  
IFR, THROUGH MUCH OF THE NIGHT AND INTO MONDAY MORNING.  
CONDITIONS WILL BE SLOW TO IMPROVE ON MONDAY BUT ARE EXPECTED TO  
RETURN TO VFR BY LATE MORNING/EARLY AFTERNOON.  
 
WINDS...EASTERLY WINDS AT THE TERMINALS TODAY HAVE REMAINED  
LIGHT, AROUND 10 KNOTS OR LESS ACROSS THE REGION. WINDS WILL  
BECOME LIGHT AND VARIABLE OVERNIGHT AND THEN BECOME MAINLY WEST  
TO NORTHWEST FOR KPHL/KILG/KMIV/KACY/KRDG AND MORE NORTH TO  
NORTHEAST FOR KTTN AND KABE FOR MONDAY. WINDS SPEEDS ARE  
EXPECTED TO REMAIN AROUND 10 KNOTS OR LESS.  
 
OUTLOOK...  
MONDAY NIGHT...CONDITIONS LOWERING TO MVFR AND POSSIBLY IFR. A  
CHANCE OF SHOWERS AND THUNDERSTORMS.  
 
TUESDAY...MVFR AND IFR CONDITIONS POSSIBLE IN THE EARLY  
MORNING, THEN VFR.  
 
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...MAINLY VFR.  
 
THURSDAY...MAINLY VFR. A CHANCE OF AFTERNOON SHOWERS AND  
THUNDERSTORMS.  
 
THURSDAY NIGHT AND FRIDAY...MVFR AND IFR CONDITIONS ARE  
POSSIBLE IN SHOWERS AND THUNDERSTORMS.  
 

 
   
MARINE
 
 
SUB-ADVISORY CONDITIONS ARE EXPECTED TO CONTINUE ON THE AREA  
WATERS THROUGH MONDAY. SEAS ARE 2 TO 4 FEET ON THE OCEAN AND  
AROUND 2 TO 3 FEET ON THE DELAWARE BAY. WHILE SEAS ARE EXPECTED  
TO REMAIN BELOW 5 FEET, THEY MAY NEAR 5 FEET LATE TONIGHT/EARLY  
MONDAY, MAINLY OUR NORTHERNMOST WATERS. ADDITIONALLY, WINDS WILL  
PICK UP SOME OVERNIGHT OUR OF THE EAST IN RESPONSE TO A SURFACE  
LOW MOVING OVER THE AREA AND A TIGHTENING PRESSURE GRADIENT.  
THE GRADIENT DOESN'T LOOK TO FULLY WRAP UP UNTIL THE SURFACE LOW  
IS TO THE EAST OF OUR AREA. WINDS MAY GUSTY BRIEFLY NEAR 25  
KNOTS BUT CONFIDENCE IS LOW THAT A SMALL CRAFT ADVISORY WILL BE  
NEEDED.  
 
SHOWERS AND THUNDERSTORMS WILL IMPACT THE AREA WATERS THROUGH  
TONIGHT, WITH LOCALLY HIGHER SEAS AND GUSTY WINDS.  
 
OUTLOOK...  
MONDAY NIGHT THROUGH FRIDAY...NO MARINE HEADLINES ARE  
ANTICIPATED.  
 
RIP CURRENTS...  
A MODERATE RISK FOR RISK CURRENTS IS EXPECTED TO CONTINUE  
THROUGH THIS EVENING FOR THE NEW JERSEY BEACHES. A LOW RISK  
REMAINS FOR THE DELAWARE BEACHES. SIMILAR CONDITIONS ARE  
EXPECTED TO CONTINUE FOR MONDAY.  
 

 
   
TIDES/COASTAL FLOODING
 
 
THERE IS COASTAL FLOOD ADVISORY IN EFFECT FOR THIS EVENING'S  
HIGH TIDE ALONG THE NEW JERSEY AND DELAWARE COASTS AND ALONG  
DELAWARE BAY.  
 
AN ONSHORE FLOW ALONG THE COAST FROM SANDY HOOK DOWN TO AROUND  
ATLANTIC CITY ALMOST GUARANTEES MINOR FLOODING FOR THE NEW  
JERSEY COAST. CONDITIONS MAY BE A BIT MARGINAL FOR DELAWARE.  
 
THE ASTRONOMICAL TIDES WILL REMAIN HIGH FOR MONDAY EVENING'S  
HIGH TIDE AND ANOTHER COASTAL FLOOD ADVISORY MAY BE NEEDED AT  
THAT TIME.  
 

 
   
EQUIPMENT
 
 
DEW POINT READINGS AT KDOV CONTINUE TO MEASURE TOO HIGH  
COMPARED TO SURROUNDING LOCATIONS AND SHOULD BE TREATED AS  
UNREPRESENTATIVE OF THE AREA.  
 
HAMBURG NJ TRANSMITTER IS OFF THE AIR. NO KNOWN RTS.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR PAZ054-055-060>062-  
070-071-101>106.  
NJ...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR NJZ001-007>010-012-  
013-015>019.  
COASTAL FLOOD ADVISORY UNTIL 1 AM EDT MONDAY FOR NJZ012>014-  
020>027.  
DE...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR DEZ001.  
COASTAL FLOOD ADVISORY UNTIL 1 AM EDT MONDAY FOR DEZ002>004.  
MD...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR MDZ008.  
MARINE...NONE.  
 

 
 

 
 
SYNOPSIS...IOVINO  
NEAR TERM...MEOLA  
SHORT TERM...MEOLA  
LONG TERM...IOVINO  
AVIATION...IOVINO/MEOLA  
MARINE...IOVINO/MEOLA  
TIDES/COASTAL FLOODING...IOVINO  
EQUIPMENT...STAFF  
 
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