628  
FXUS61 KPHI 241353  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
953 AM EDT SUN JUN 24 2018  
   
SYNOPSIS
 
 
A COLD FRONT WILL PROGRESS THROUGH THE REGION LATE TODAY. HIGH  
PRESSURE OVER ONTARIO BUILDS INTO THE REGION TOMORROW AND SLOWLY  
MOVES OFF THE EASTERN SEABOARD. A WARM FRONT SHOULD ARRIVE ON  
WEDNESDAY FOLLOWED BY A SLOW MOVING TROUGH WHICH SHOULD BE IN OUR  
REGION THURSDAY INTO FRIDAY. HIGH PRESSURE BUILDS IN FOR NEXT  
WEEKEND.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
THE FOG HAS DISSIPATED THIS MORNING EXCEPT FOR THE SOUTHERN  
PORTIONS OF THE NJ COAST. BEACH CAMS AND SAT PIX STILL SHOWS  
SOME RESTRICTIONS FROM ABOUT MANASQUAN SOUTH. THIS FOG IS ALSO  
EXPECTED TO DISSIPATE.  
 
FOR THE MORNING UPDATE, I BUMPED UP TEMPS A DEGREE OR TWO ACROSS  
THE DELMARVA, AND PER SHORT-TERM HI-RES MODELS, ALSO ADJUSTED  
THE SPEED AND AREAL EXTENT OF THE SHOWERS AND THUNDERSTORMS.  
TIMING-WISE, EXPECT THE BEST CHANCE OF THUNDERSTORMS IN THE  
LEHIGH VALLEY BETWEEN 22Z-01Z, THE I95 CORRIDOR BETWEEN 23Z-  
02Z, AND AT THE BEACHES BETWEEN 00-03Z.  
 
PREVIOUS DISCUSSION...  
AREAS OF FOG THROUGH MID-MORNING MAY REDUCE VISIBILITY TO 1/4  
MILE AT TIMES. PARTLY SUNNY SKIES WILL DEVELOP INTO THE EARLY  
AFTERNOON. COMPARED TO YESTERDAY'S STOUT INVERSION DUE TO A  
MARITIME AIRMASS, EXPECT MIXING TODAY TO ELEVATE TEMPERATURES  
INTO THE 80S REGIONWIDE, WITH 70S IN THE SOUTHERN POCONOS AND  
BARRIER ISLANDS. A MID-LEVEL TROUGH AND AND ATTENDANT COLD FRONT  
WILL APPROACH FROM THE WEST LATE IN THE DAY. THE 00Z HREF  
INDICATES ML CAPE APPROACHING 1000 J/KG, AND BULK SHEAR ALSO  
INCREASES UP TO 40 KT. WHILE HIGHER CAPE VALUES ARE ACROSS THE  
SOUTHERN PART OF THE AREA, GREATER BULK SHEAR IS TO THE NORTH.  
THE MAJORITY OF THE HREF MEMBERS INDICATE TWO AREAS OF ACTIVITY:  
NORTH OF I-78 AND NEAR THE MASON DIXON LINE. THE MAIN CONCERN  
WOULD BE THE POTENTIAL FOR GUSTY WINDS AND HEAVY DOWNPOURS.  
WHILE GREATER DCAPE AND 0-3 KM LAPSE RATES FROM THE I-95  
CORRIDOR EAST WOULD MAKE THIS THE AREA MOST SUSCEPTIBLE TO GUSTY  
WINDS, MID- LEVEL DRY AIR AND MODEST BULK SHEAR MAY LIMIT BOTH  
COVERAGE AND ORGANIZATION. WITH PRECIPITABLE WATER VALUES  
DECREASING CLOSER TO 1.5 INCHES THIS AFTERNOON AND PROGRESSIVE  
CELL MOVEMENT, THE THREAT FOR URBAN AND POOR DRAINAGE FLOODING  
IS LOW.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/
 
 
THE COLD FRONT IS PROGGED ALONG THE COAST BY 03Z WITH THUNDERSTORMS  
ENDING AROUND THIS TIME. SHOWERS ARE POSSIBLE UNTIL MIDNIGHT ACROSS  
THE SOUTHERN POCONOS AND COASTAL AREAS, BEFORE THE MID-LEVEL TROUGH  
AXIS MOVES THROUGH. DESPITE PARTIAL CLEARING AND THE MOIST GROUND,  
EXPECT NORTHWEST WINDS TO BE SUFFICIENTLY HIGH TO PRECLUDE AREAS OF  
FOG ACROSS THE REGION. SHELTERED LOCATIONS TO THE NORTHWEST OF I-95  
COULD EXPERIENCE PATCHY FOG. LOW TEMPERATURES AT SEASONAL  
LEVELS.  
 

 
   
LONG TERM /MONDAY THROUGH SATURDAY/
 
 
SUMMARY: HIGH PRESSURE WILL BRING TRANQUIL WEATHER MONDAY AND  
TUESDAY. CHANCES FOR SHOWERS AND THUNDERSTORMS AGAIN INCREASE  
WEDNESDAY THROUGH THURSDAY AS FIRST A WARM FRONT AND THEN A  
TROUGH APPROACH OUR REGION. TRANQUIL, BUT HOT, WEATHER SHOULD  
RETURN BY NEXT WEEKEND AS A HIGH BUILDS INTO THE REGION.  
 
DETAILS:  
MONDAY AND TUESDAY...CANADIAN HIGH PRESSURE BUILDS SOUTH. THE  
MAIN IMPACT WITH THE COLD FRONT LATER TODAY IS THAT DEW POINTS  
WILL BE MUCH LOWER THAN WHAT WE HAVE SEEN LATELY. I DON'T HAVE A  
SIGNIFICANT COOLING TREND WITH TEMPERATURES. FORECAST  
TEMPERATURES ARE HIGHER THAN MOST GUIDANCE AS THE PATTERN  
FAVORS VERY LARGE DEW POINT DEPRESSIONS IN THE BOUNDARY LAYER.  
MODELS TYPICALLY UNDERESTIMATE THE DEPTH OF THE MIXING LAYER IN  
THESE CASES WHICH COULD RESULT IN HIGHER THAN FORECAST MAX  
TEMPERATURES AND LOWER THAN FORECAST DEW POINTS.  
 
WEDNESDAY AND THURSDAY...A LARGE LOW PRESSURE SYSTEM, TRACKING  
ACROSS THE GREAT LAKES REGION, WILL FIRST BRING A WEAK COLD  
FRONT INTO THE REGION LATE WEDNESDAY, FOLLOWED BY A SLOW MOVING  
TROUGH WEDNESDAY NIGHT INTO THURSDAY NIGHT. SOME GUIDANCE BACKED  
OFF ON THE EXTENT OF PRECIPITATION COVERAGE, ESPECIALLY ON  
WEDNESDAY. THIS MAKES SENSE GIVEN HOW MUCH MOISTURE ADVECTION  
WILL NEED TO TAKE PLACE BEFORE WE GET A NEARLY SATURATED LAYER  
IN THE LOW OR MID LEVELS. SOUTHERLY LOW LEVEL RETURN FLOW  
SHOULD DEVELOP BY LATE WEDNESDAY, RESULTING IN MOISTURE AND  
WARM AIR ADVECTION. THE PRIME PERIOD FOR PRECIPITATION STILL  
LOOKS TO BE LATE WEDNESDAY NIGHT INTO THE DAY TIME HOURS ON  
THURSDAY, BUT ALSO HAVE A CHANCE WEDNESDAY AND THURSDAY NIGHT.  
 
FRIDAY AND SATURDAY...A HIGH SHOULD START BUILDING IN FROM THE  
SOUTHWEST. THE BIGGEST DIFFERENCES FROM THE MODELS YESTERDAY IS  
THAT MANY OF THE CURRENT RUNS DEPICT THE CENTER OF THE HIGH  
STALLING NORTH OF OUR REGION, LEAVING US WITH LIGHT ON SHORE  
FLOW THROUGH THE WEEKEND. IF IT DEVELOPS THIS WAY, THE MARINE  
LAYER COULD MAKE THE DIFFERENCE BETWEEN NO EXCESSIVE HEAT  
HEADLINES AND EXCESSIVE HEAT HEADLINES FOR MUCH OF OUR AREA. I  
AM UNCERTAIN IF IT WILL ACTUALLY DEVELOP THIS WAY, SO I STAYED  
CLOSE TO THE PREVIOUS FORECAST, WITH HIGHS GENERALLY IN THE  
LOWER TO MID 90S (ESPECIALLY SATURDAY).  
 

 
   
AVIATION /14Z SUNDAY THROUGH THURSDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TODAY...  
WIDESPREAD LIFR CONDITIONS IN LOW CLOUDS AND FOG WILL RAPIDLY  
IMPROVE GENERALLY IN THE 12Z-16Z TIME FRAME TO VFR AT ALL TAF  
SITES. BRIEF CEILING AND VISIBILITY RESTRICTIONS ARE POSSIBLE  
IN AFTERNOON AND EVENING THUNDERSTORMS. SOUTHWEST WINDS 10-15  
KT WITH HIGHER GUSTS POSSIBLE IN THUNDERSTORMS. FORECASTER  
CONFIDENCE IS MEDIUM, EXCEPT LOW REGARDING SPECIFIC TIMING OF  
LIFR TO VFR TRANSITION AT INDIVIDUAL TAF SITES.  
 
TONIGHT...  
VFR CONDITIONS. SOUTHWEST WINDS VEERING TO NORTHWEST 10-15 KT.  
HIGH CONFIDENCE.  
 
OUTLOOK...  
MONDAY AND TUESDAY...VFR CONDITIONS ARE EXPECTED. NORTHWESTERLY  
WINDS ON MONDAY BECOME LIGHT AND VARIABLE MONDAY NIGHT INTO  
TUESDAY. HIGH CONFIDENCE.  
 
WEDNESDAY...MOSTLY VFR CONDITIONS ARE EXPECTED. THERE IS A  
CHANCE FOR SHOWERS AND THUNDERSTORMS TO MOVE IN THROUGH THE DAY,  
ESPECIALLY AT KABE AND KRDG. IF THIS HAPPENS, MVFR CONDITIONS  
WILL BE POSSIBLE. INCREASING SOUTHERLY WINDS POSSIBLE THROUGH  
THE DAY. MODERATE CONFIDENCE.  
 
WEDNESDAY NIGHT AND THURSDAY...A PERIOD OF MVFR CONDITIONS IS  
POSSIBLE BOTH DUE TO LOW CLOUDS AND SHOWERS AND THUNDERSTORMS.  
SOUTHERLY WINDS OF 10 TO 15 KT IS ALSO POSSIBLE FOR AT LEASE A  
PORTION OF THIS PERIOD. LOW CONFIDENCE.  
 

 
   
MARINE
 
 
TODAY...SOUTHWEST WINDS 10-15 KT WITH GUSTS AROUND 20 KT POSSIBLE.  
SEAS 2-4 FT. FOG EARLY THIS MORNING WILL RESTRICT VSBY TO 2 NM OR  
LESS, BUT SHOULD DISSIPATE BY THIS AFTERNOON. SUB-SCA CONDITIONS.  
 
TONIGHT...SOUTHWEST WINDS AROUND 10 KT GRADUALLY BECOMING NORTHWEST  
10-15 KT WITH GUSTS AROUND 20 KT AFTER MIDNIGHT. SEAS 2-4 FT. SUB-  
SCA CONDITIONS.  
 
OUTLOOK...  
 
MONDAY AND TUESDAY...WINDS AND SEAS SHOULD STAY BELOW SCA  
CRITERIA.  
 
WEDNESDAY AND THURSDAY...SCA CONDITIONS, FOR BOTH WINDS AND  
SEAS, ARE LIKELY ON THE ATLANTIC COASTAL WATERS. SCA CONDITIONS,  
MAINLY FOR WINDS ARE POSSIBLE ON THE DELAWARE BAY. SOUTHERLY  
WINDS INCREASE AHEAD OF THE NEXT LOW PRESSURE SYSTEM. SEAS  
SHOULD SUBSEQUENTLY INCREASE AS WELL.  
 
RIP CURRENTS...  
SOUTHWEST WINDS 10-20 MPH, WAVE HEIGHTS 2-4 FEET, AND A DOMINANT  
SOUTHEASTERLY SWELL PERIOD 6-7 SECONDS YIELDS A LOW RISK FOR THE  
DEVELOPMENT OF DANGEROUS RIP CURRENTS FOR THE DE AND NJ BEACHES.  
 

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

 
 

 
SYNOPSIS...JOHNSON  
NEAR TERM...KRUZDLO/LF  
SHORT TERM...LF  
LONG TERM...JOHNSON  
AVIATION...JOHNSON/LF  
MARINE...JOHNSON/LF  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab PA Page
The Nexlab NJ Page
The Nexlab DE Page
The Nexlab MD Page Main Text Page