788  
FXUS61 KPHI 271641  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
ISSUED BY NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC  
1241 PM EDT THU APR 27 2017  
   
SYNOPSIS
 
 
A COLD FRONT WILL MOVE ACROSS THE AREA TONIGHT INTO FRIDAY  
MORNING. A BACKDOOR COLD FRONT WILL MOVE ACROSS THE AREA  
SATURDAY INTO SATURDAY NIGHT. THIS FRONT WILL REMAIN TO OUR  
SOUTH ON SUNDAY, THEN RETURN AS A WARM FRONT ON SUNDAY NIGHT.  
ANOTHER COLD FRONT IS EXPECTED ON MONDAY NIGHT, WITH A SECONDARY  
FRONT OR SURFACE TROUGH TUESDAY. ANOTHER COLD FRONT IS POSSIBLE  
WEDNESDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
CLEARING OF THE LOW CLOUDS CONTINUES SLOWLY FROM SOUTHWEST TO  
NORTHEAST, WITH THE EXCEPTION OF LOW MARINE STRATUS ALONG THE  
IMMEDIATE SOUTHERN NJ COASTLINE. FORECAST FOR TODAY REMAINS ON  
TRACK.  
 
PREVIOUS DISCUSSION FROM 950AM:  
LOW CONTINUES TO SPIN AWAY FROM THE REGION THIS MORNING, WITH  
MID/UPPER LEVEL RIDGING MOVING OVERHEAD AHEAD OF THE NEXT SYSTEM  
EJECTING THROUGH THE GREAT LAKES THAT WILL AFFECT THE REGION  
TONIGHT. LINGERING LOW LEVEL MOISTURE AND LOW LEVEL  
SOUTHEASTERLY FLOW HAS LED TO THE CONTINUATION OF LOW CLOUDS  
FROM THE PHILADELPHIA METRO AREA NORTHEASTWARD AND ALONG THE  
SHORELINES. THERE IS ALSO STILL SOME LINGERING FOG IN THE  
POCONOS THIS MORNING. GRADUAL IMPROVEMENT IS EXPECTED THROUGH  
THE MORNING HOURS AND INTO THE AFTERNOON, ESPECIALLY ACROSS SE  
PA, CENTRAL AND SOUTHERN NJ, AND DE, WITH MOSTLY SUNNY SKIES  
ALREADY BEING OBSERVED SW OF THE PHILLY METRO AS OF 930 AM. NE  
PA AND NORTHERN NJ WILL BE THE TOUGHEST TO GET SUNSHINE. HIGHS  
TODAY IN THE 70S FOR MOST LOCATIONS, WITHIN A FEW DEGREES  
PLUS/MINUS OF 80F FOR PHILLY SW-WARD, AND STUCK IN THE 60S ALONG  
THE IMMEDIATE SHORELINE WITH CONTINUED SE FLOW.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/
 
 
THE MAIN STORY TONIGHT WILL BE THE COLD FRONT EXPECTED TO MOVE  
THROUGH THE REGION. WITH THE CENTER OF THE ASSOCIATED SURFACE  
LOW (IN CENTRAL CANADA) SLOWLY PROPAGATING NORTH, THE FRONT IS  
NOT EXPECTED TO PROGRESS EAST VERY QUICKLY. EXPECT THAT MOST  
PRECIPITATION AHEAD OF AND WITH THE FRONT WILL BE SHOWERS.  
HOWEVER, MODEL SOUNDINGS DO SHOW ELEVATED INSTABILITY, THUS HAVE  
KEPT MENTION OF THUNDERSTORMS OVERNIGHT.  
 
GIVEN PERSISTENT CLOUD COVER OVERNIGHT, AND A LATE ARRIVAL OF  
THE COLD FRONT, DO NOT EXPECT TEMPERATURES TO DROP OFF MUCH  
OVERNIGHT, WITH LOWS GENERALLY IN THE UPPER 50S AND LOWER 60S.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
THE COLD FRONT THAT AFFECTS THE AREA THURSDAY MOVES OFFSHORE  
FRIDAY MORNING AND ANY SHOWERS WILL DISSIPATE AND/OR MOVE  
OFFSHORE THROUGH THE MORNING AS WELL. THE REMAINDER OF FRIDAY  
WILL REMAIN DRY AS WEAK HIGH PRESSURE BRIEFLY AFFECTS THE AREA.  
 
BY FRIDAY NIGHT, ANOTHER FRONTAL BOUNDARY IS FORECAST TO BEGIN  
APPROACHING THE AREA FROM THE NORTH AS IT CROSSES PENNSYLVANIA  
AND NEW YORK. THE FRONT IS NOT EXPECTED TO MOVE INTO THE AREA  
UNTIL LATER SATURDAY, THEN SINK TO OUR SOUTH SATURDAY NIGHT.  
SATURDAY'S HIGH TEMPERATURES WILL BE HIGHLY DEPENDENT ON HOW  
FAST THE FRONT MOVES THROUGH THE AREA. IF IT WAITS UNTIL THE  
LATE AFTERNOON/EVENING, TEMPERATURES WILL BE ABLE TO WARM QUITE  
SIGNIFICANTLY. HOWEVER, IF THE FRONT MOVES THROUGH QUICKER, HIGH  
TEMPERATURES MAY NOT BE AS HIGH AS CURRENTLY FORECAST. THIS  
WOULD BE MORE LIKELY ACROSS PORTIONS OF NORTHEAST PENNSYLVANIA  
AND NORTHERN NEW JERSEY WHERE THE FRONT MAY CROSS SOONER. A  
COUPLE OF SHORT WAVE/VORTICITY IMPULSES ARE FORECAST TO MOVE  
ACROSS THE AREA FRIDAY NIGHT THROUGH SATURDAY NIGHT, SO THERE  
WILL BE A CHANCE FOR ISOLATED/SCATTERED SHOWERS.  
 
THE FRONT WILL STALL TO OUR SOUTH DURING THE DAY SUNDAY, WHICH  
SHOULD ALLOW SUNDAY TO BE MOSTLY DRY, BUT AN ISOLATED SHOWER CAN  
NOT BE RULED OUT. BEING THE FRONT IS A BACK-DOOR FRONT COMING  
FROM THE NORTH, IT WILL BRING COOLER CONDITIONS ON SUNDAY.  
SUNDAY'S HIGHS ARE FORECAST TO BE MARKEDLY COOLER THAN SATURDAY.  
15 DEGREES COOLER FOR MANY AREAS.  
 
THE FRONT WILL NOT STAY TO OUR SOUTH VERY LONG AS IT IS  
EXPECTED TO LIFT BACK NORTHWARD AS A WARM FRONT SUNDAY  
NIGHT/MONDAY MORNING. AS THE FRONT LIFTS ACROSS THE AREA, THERE  
WILL BE A CHANCE OF SHOWERS SUNDAY NIGHT INTO MONDAY MORNING.  
THERE COULD ALSO BE SOME SHOWERS AND THUNDERSTORMS DEVELOPING  
DURING THE DAY MONDAY AHEAD OF AN APPROACHING COLD FRONT.  
 
HOWEVER, THE BEST CHANCE FOR SHOWERS AND THUNDERSTORMS MONDAY  
NIGHT AS A COLD FRONT APPROACHES FROM THE WEST. BEING WE SHOULD  
ENTER INTO THE WARM SECTOR DURING THE DAY, WE SHOULD WARM QUITE  
NICELY, AND IN TURN SOME INSTABILITY SHOULD BUILD AHEAD OF THE  
FRONT. THEREFORE THERE WILL BE A CHANCE OF THUNDERSTORMS MONDAY  
AFTERNOON AND MONDAY NIGHT.  
 
THE FRONT WILL MOVE OFFSHORE BY TUESDAY MORNING, BUT A  
SECONDARY SURFACE TROUGH MAY MOVE ACROSS THE AREA DURING THE DAY  
TUESDAY. WITH A SHORT WAVE/VORTICITY MOVING ACROSS THE AREA  
DURING THE DAY, THERE COULD BE SOME ISOLATED SHOWERS ACROSS  
NORTHEASTERN PENNSYLVANIA AND NORTHERN NEW JERSEY.  
 
ANOTHER FRONT MAY MOVE ACROSS THE ARE WEDNESDAY OF NEXT WEEK  
WHICH COULD BRING ANOTHER CHANCE OF SHOWERS. THE GFS AND  
CANADIAN CONTINUE DEVELOPING AN AREA OF LOW PRESSURE ALONG THE  
FRONT TO OUR SOUTHEAST WHICH COULD MOVE ACROSS OUR AREA LATER IN  
THE WEEK. HOWEVER, THE ECMWF NO LONGER HAS THIS FEATURE. THIS  
IS STILL PRETTY FAR OUT, BUT THERE WILL BE A CHANCE OF SHOWERS  
IN THE FORECAST FOR THE END OF NEXT WEEK.  
 

 
   
AVIATION /18Z THURSDAY THROUGH TUESDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
THE STERLING OFFICE WILL BE UPDATING TAFS AFTER 1230Z TODAY  
SINCE THE MOUNT HOLLY OFFICE WILL BE OFF LINE FOR A COMPUTER  
UPGRADE INTO THIS AFTERNOON.  
 
TODAY...CONDITIONS IMPROVING EARLY THIS AFTERNOON WITH MVFR  
CONDITIONS GIVING WAY TO VFR AS LOW CLOUDS ERODE. WINDS MAINLY  
SOUTHEAST TO SOUTH AND MAY GUST 15-20 KT AT TIMES DURING MID  
AFTERNOON.  
 
TONIGHT...AFTER 03Z, LOW CLOUDS MAY MOVE BACK IN OVER THE REGION.  
IN ADDITION, SHOWERS AND ISOLATED THUNDERSTORMS MAY APPROACH  
FROM THE WEST. THERE IS LOW CONFIDENCE THOUGH ON IF INDIVIDUAL  
TAF SITES WILL BE AFFECTED AND THE TIMING. SOUTHERLY WINDS  
TONIGHT SHIFT WEST LATE AFTER FRONTAL PASSAGE.  
 
OUTLOOK...  
 
FRIDAY...VFR CONDITIONS EXPECTED.  
 
FRIDAY NIGHT...VFR EARLY. PATCHY FOG AND LOW CIGS MAY DEVELOP  
OVERNIGHT.  
 
SATURDAY...BECOMING VFR DURING THE MORNING, THEN A CHANCE OF  
SHOWERS DURING THE AFTERNOON. CONDITIONS MAY TEMPORARILY BE  
REDUCED WITH ANY SHOWERS. GUSTY WESTERLY WINDS 15-20 KNOTS.  
 
SATURDAY NIGHT-SUNDAY NIGHT...LOW CLOUDS AND FOG MAY DEVELOP  
OVERNIGHT SATURDAY AND CONTINUE INTO SUNDAY NIGHT LEADING TO  
REDUCED CONDITIONS. SMALL CHANCE OF SHOWERS AND THUNDERSTORMS.  
CONDITIONS MAY TEMPORARILY BE REDUCED WITH ANY SHOWERS.  
 
MONDAY...LOW CONDITIONS IN THE MORNING, BECOMING VFR DURING THE  
DAY. A CHANCE OF SHOWERS THUNDERSTORMS DURING THE DAY, WITH  
MORE LIKELY SHOWERS AND THUNDERSTORMS OVERNIGHT. LOWER  
CONDITIONS POSSIBLE DURING THE DAY WITH ANY SHOWERS OR STORMS,  
MORE LIKELY LOWER CONDITIONS OVERNIGHT. GUSTY SOUTHWEST WINDS  
AROUND 25 KNOTS.  
 

 
   
MARINE
 
 
ELEVATED SEAS ARE EXPECTED TO CONTINUE TODAY AND TONIGHT ON THE  
ATLANTIC COASTAL WATERS, GENERALLY RANGING FROM 5 TO 6 FEET. A  
FEW GUSTS NEAR OR ABOVE 20 KT ARE POSSIBLE THIS EVENING.  
 
OUTLOOK...  
 
FRIDAY...WINDS EXPECTED TO REMAIN BELOW ADVISORY LEVELS, BUT  
SEAS MAY REMAIN ELEVATED TO ADVISORY LEVELS.  
 
FRIDAY NIGHT-SUNDAY NIGHT...SEAS MAY APPROACH 5 FEET AT TIMES,  
AND WINDS MAY GUST NEAR 20 KNOTS, BUT CONDITIONS EXPECTED TO  
REMAIN BELOW ADVISORY LEVELS.  
 
MONDAY...WINDS LIKELY TO GUST 25-30 KNOTS, AND SEAS LIKELY TO  
EXCEED 5 FEET AS WELL LEADING TO SMALL CRAFT ADVISORY  
CONDITIONS.  
 

 
   
TIDES/COASTAL FLOODING
 
 
THOUGH SOME OF THE GUIDANCE IS DEPICTING MINOR COASTAL FLOODING  
WITH THE EVENING HIGH TIDES TODAY AND TOMORROW, WE ARE NOT  
EXPECTING ANY COASTAL FLOODING AS ASTRONOMICAL TIDES WILL START  
TO DECREASE, AND BY TONIGHT, WINDS WILL BE SHIFTING TO OFF  
SHORE.  
 

 
   
CLIMATE
 
 
PRESUMING OUR FORECAST TEMPS THESE LAST 5 DAYS OF APRIL ARE  
ACCURATE, WE ARE ASSURED OF A TOP 3 WARMEST APRIL ON RECORD IN  
MUCH OF OUR FORECAST AREA. SUNDAY IS THE CRITICAL DAY FOR  
DETERMINING RECORD OR NOT. (WILL RECHECK THIS PROJECTION AROUND  
430 PM)  
 
BELOW: APRIL PROJECTED WITHIN THE TOP APRIL AVG TEMPS, THE  
NORMAL FOR APRIL AND THE PERIOD OF RECORD (POR).  
 
PHL NORMAL 54.0 POR 1874  
 
59.4 1994  
59.2 2017?  
58.5 1921  
58.4 2010  
57.9 1941  
 
ABE NORMAL 49.9 POR 1922  
 
56.6 PROJECTING RECORD  
56.4 1941  
54.7 1994  
 
ACY NORMAL 51.7 POR 1874  
 
57.2 PROJECTING RECORD  
56.3 2010  
56.1 2011  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 AM EDT FRIDAY  
FOR ANZ450>455.  
 

 
 

 
SYNOPSIS...ROBERTSON  
NEAR TERM...MUCCILLI  
SHORT TERM...JOHNSON  
LONG TERM...ROBERTSON  
AVIATION...MUCCILLI/DRAG/JOHNSON/ROBERTSON 803  
MARINE...JOHNSON/ROBERTSON  
TIDES/COASTAL FLOODING...PHI  
CLIMATE...803  
 
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