143  
FXUS61 KPHI 190141  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
941 PM EDT MON JUN 18 2018  
   
SYNOPSIS
 
 
A COLD FRONT WILL MOVE ACROSS THE AREA TONIGHT INTO TUESDAY,  
BEFORE PUSHING SOUTH OF THE AREA LATER TUESDAY INTO TUESDAY  
NIGHT. WEAK HIGH PRESSURE WILL BRIEFLY AFFECT THE AREA TUESDAY  
NIGHT, BEFORE SHIFTING OFFSHORE WEDNESDAY. AN AREA OF LOW  
PRESSURE WILL DEVELOP ALONG THIS BOUNDARY ACROSS THE OHIO RIVER  
VALLEY ON WEDNESDAY, THEN MOVE EASTWARD ALONG THIS BOUNDARY  
WEDNESDAY INTO WEDNESDAY NIGHT, WHILE A COLD FRONT MOVES ACROSS  
THE AREA FROM THE NORTH. HIGH PRESSURE BUILDS ACROSS THE  
NORTHEAST THURSDAY NIGHT, BEFORE SHIFTING OFFSHORE FRIDAY. A  
WARM FRONT IS EXPECTED TO LIFT ACROSS THE AREA LATER SATURDAY,  
FOLLOWED WITH A COLD FRONT ON SUNDAY INTO SUNDAY NIGHT.  
 

 
   
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
 
 
A BROKEN LINE OF SHOWERS AND THUNDERSTORMS CONTINUES TO  
DISSIPATE AS IT TRACKS SE THROUGH NJ AND INTO PHILLY. LOCALLY  
HEAVY RAIN, FREQUENT LIGHTNING STRIKES, AND LOCALLY DAMAGING  
WINDS POSSIBLE FOR THE NEXT HOUR OR SO.  
 
CONDITIONS THEN SHOULD BE RELATIVELY QUIET UNTIL AFTER  
MIDNIGHT. COLD FRONT EXTENDING FROM EASTERN CANADA, THROUGH  
JUST NORTH OF NY STATE, AND BACK THROUGH THE GREAT LAKES WILL  
APPROACH, AND SHOWERS AND THUNDERSTORMS WILL FIRE UP AHEAD OF  
THAT FRONT. WITH TEMPERATURES FALLING, THE AIRMASS WILL BECOME  
MORE STABLE GOING THROUGH THE OVERNIGHT, BUT THERE WILL STILL BE  
AROUND 1000-1500 J/KG OF ML MUCAPE AHEAD OF THE FRONT. LINE OF  
SHOWERS AND THUNDERSTORMS CURRENTLY EXTENDING FROM SOUTH-CENTRAL  
NY STATE BACK THROUGH NW PA, AND ARE TRACKING TO THE SOUTHWEST.  
BY THE TIME THEY REACH THE SOUTHERN POCONOS AND LEHIGH VALLEY,  
IT SHOULD BE AROUND MIDNIGHT OR SO, AND CURRENT RADAR TRENDS  
MATCH UP FAIRLY WELL WITH THE LATEST HRRR TRENDS. 0-6 KM SHEAR  
VALUES WILL INCREASE TO 30-35 KT, SO DESPITE THE DECREASE IN  
INSTABILITY, THERE SHOULD BE ANOTHER ROUND OF STRONG TO LOCALLY  
SEVERE THUNDERSTORMS GOING THROUGH THE OVERNIGHT.  
 
HI-RES GUIDANCE INDICATES THIS LINE OF CONVECTION WILL PASS  
THROUGH THE REGION AS THE COLD FRONT WORKS ITS WAY SOUTH THROUGH  
THE REGION, AND MOVE OFF THE SOUTHEAST NJ COAST BY DAYBREAK OR  
SO. STORMS SHOULD WEAKEN A BIT ONCE THEY GET SOUTH OF THE FALL  
LINE. WITH PWATS UP AROUND 2", CAN EXPECT HEAVY RAIN WITH ANY  
STORMS, BUT THEY SHOULD BE FAIRLY QUICK MOVERS, AND NOT  
EXPECTING WIDESPREAD FLOODING CONCERNS. CANNOT RULE OUT SOME  
LOCALIZED POOR DRAINAGE FLOODING. COLD FRONT WILL BE THROUGH THE  
SOUTHERN POCONOS AND NORTHERN NJ, AND WILL BE INTO THE LEHIGH  
VALLEY BY DAYBREAK TUESDAY.  
 
WARM AND MUGGY WITH LOWS GENERALLY IN THE 70S, AND SURFACE  
DEWPOINTS NOT MUCH LOWER.  
 

 
   
SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/
 
 
THE AFORMENTIONED COLD FRONT WILL BE SITUATED CLOSE TO THE I-95  
CORRIDOR ACROSS SE PA TO START THE DAY BUT WILL CONTINUE TO  
PROGRESS SLOWLY SOUTHWARD THROUGH THE DAY. THE GOOD NEWS IS THIS  
WILL LEAD TO A DRYING TREND WITH LOWERING DEW POINTS FROM NORTH  
TO SOUTH. THIS WILL RESULT IN CONDITIONS FEELING MUCH MORE  
COMFORTABLE BY AFTERNOON EXCEPT ACROSS THE DELMARVA WHERE  
HUMIDITY WILL LINGER CLOSER TO THE FRONT. ALONG AND SOUTH OF THE  
COLD FRONT, THERE WILL CONTINUE TO BE CHANCES FOR SOME SHOWERS  
AND STORMS WITH MOST OF THIS ACTIVITY OCCURING IN THE AFTERNOON  
OVER THE DELMARVA COINCIDING WITH PEAK HEATING. NOT EXPECTING  
ANY OF THESE STORMS TO BE SEVERE THOUGH AS THE BEST INSTABILITY  
SHOULD BE JUST TO THE SOUTH. FARTHER NORTH ACROSS SE PA AND  
CENTRAL AND NORTHERN NJ ANY EARLY MORNING SHOWERS AND ISOLATED  
STORMS WITH THE FRONT WILL GIVE WAY TO CLEARING BY AFTERNOON  
WITH THE N/NW FLOW BEHIND THE FRONT. HIGHS WILL GENERALLY BE IN  
THE 80S TO AROUND 90 BUT WITH FALLING DEW POINTS SO WE WON'T SEE  
THE HIGH HEAT INDICIES OF TODAY. ALSO, A SEA BREEZE IS LIKELY  
IN THE AFTERNOON BRINGING COOLER TEMPERATURES ALONG THE COAST.  
 

 
   
LONG TERM /TUESDAY NIGHT THROUGH MONDAY/
 
 
WEAK HIGH PRESSURE IS EXPECTED TO BRIEFLY BUILD ACROSS THE  
NORTHEAST TUESDAY NIGHT AS THE COLD FRONT CONTINUES TO SAG SOUTH  
OF THE AREA. THIS IS EXPECTED TO LEAD TO DRY CONDITIONS ACROSS  
THE AREA THROUGH THE OVERNIGHT PERIOD.  
 
THE WEAK HIGH PRESSURE BUILDS OFFSHORE ON WEDNESDAY, WHILE THE  
FRONTAL BOUNDARY REMAINS TO OUR SOUTH. DURING THE DAY, AN AREA  
OF LOW PRESSURE IS FORECAST TO DEVELOP ALONG THIS BOUNDARY  
ACROSS THE OHIO RIVER VALLEY AND BEGIN MOVING EASTWARD ALONG THE  
BOUNDARY. A SHORT WAVE/VORTICITY IMPULSE IS FORECAST TO MOVE  
ACROSS THE AREA WELL AHEAD OF THE ACTUAL LOW, SO THERE COULD BE  
SOME SCATTERED SHOWERS/THUNDERSTORMS DEVELOP DURING THE DAYTIME.  
OVERNIGHT, THE ACTUAL LOW ITSELF WILL MOVE ACROSS THE AREA,  
WHICH WILL ALSO LIKELY LEAD TO SCATTERED SHOWERS AND  
THUNDERSTORMS.  
 
ON THURSDAY, THE FRONT WILL HAVE PUSHED SOUTH OF THE AREA WHILE  
AN AREA OF HIGH PRESSURE BEGINS TO APPROACH FROM THE NORTHWEST.  
THE HIGH WILL FULLY BUILD ACROSS THE NORTHEAST THURSDAY NIGHT,  
BEFORE SHIFTING OFFSHORE FRIDAY. THIS WILL LEAD TO FAIR  
CONDITIONS THROUGH FRIDAY.  
 
HOWEVER, AS WE GO INTO FRIDAY NIGHT AND INTO THE WEEKEND, SOME  
UNSETTLED WEATHER RETURNS TO THE FORECAST. WITH THE HIGH  
OFFSHORE OF THE EAST COAST, RETURN FLOW STRENGTHENS ACROSS THE  
AREA, WHICH WILL ALLOW FOR WARM/MOIST AIR TO RETURN TO THE  
FORECAST. THE FRONT TO OUR SOUTH WILL RETURN NORTHWARD AS A WARM  
FRONT AS AN AREA OF LOW PRESSURE LIFTS THROUGH THE GREAT LAKES  
SATURDAY. THE WARM FRONT IS LIKELY TO LIFT INTO THE AREA LATER  
SATURDAY INTO SATURDAY NIGHT. WHILE THE WARM FRONT MAY BE SOUTH  
OF THE AREA ON FRIDAY NIGHT, THERE COULD BE A COUPLE OF SHORT  
WAVE/VORTICITY IMPULSES LIFT ACROSS THE AREA TO CREATE SOME  
ISOLATED SHOWERS OVERNIGHT. BUT AS WE MOVE INTO SATURDAY AND  
SATURDAY NIGHT WHEN THE FRONT GETS CLOSER TO THE AREA AND  
EVENTUALLY PASSES THROUGH, THE CHANCES OF SHOWERS AND  
THUNDERSTORMS INCREASE.  
 
THE AFOREMENTIONED LOW PRESSURE WILL MOVE ACROSS SOUTHEASTERN  
CANADA SATURDAY NIGHT INTO SUNDAY, EVENTUALLY DRAGGING A COLD  
FRONT ACROSS THE EAST COAST ON SUNDAY. THERE WILL REMAIN A  
CHANCE OF SCATTERED SHOWERS AND THUNDERSTORMS THROUGH SUNDAY AND  
SUNDAY NIGHT AS THE COLD FRONT MOVES ACROSS THE AREA.  
 
AN AREA OF LOW PRESSURE MAY DEVELOP ALONG THE FRONT AS IT MOVES  
SOUTH OF THE AREA SUNDAY NIGHT INTO MONDAY. HOWEVER, DEPENDING  
ON HOW FAR SOUTH THE FRONT SAGS TO OUR SOUTH, SHOWER AND  
THUNDERSTORM CHANCES COULD CONTINUE INTO MONDAY OF NEXT WEEK.  
 

 
   
AVIATION /01Z TUESDAY THROUGH SATURDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TONIGHT...INITIAL LINE OF SHRA/TSRA MOVING SOUTH AND EAST OF  
THE I-95 CORRIDOR TERMINALS AND CONTINUES TO WEAKEN. KACY MAY BE  
IMPACTED FROM AROUND 02Z-03Z. OTHER LINE OF SHOWERS AND  
THUNDERSTORMS WILL APPROACH KABE/KRDG AROUND MIDNIGHT TONIGHT,  
AND THEN THAT LINE WILL IMPACT THE I-95 CORRIDOR TERMINALS  
(KTTN-KPNE-KPHL-KILG) FROM AROUND 05-08Z, AND THEN KMIV-KACY  
FROM 08Z-10Z, BUT STORMS SHOULD WEAKEN BY THEN. BRIEF MVFR,  
POSSIBLY IFR VSBY IN HEAVY RAIN, OTHERWISE, VFR. SW WINDS 5-10  
KT, BECOMING W LATE, AND POSSIBLY NW AT KRDG/KABE.  
 
TUESDAY...MAINLY A VFR FORECAST. SOME SHRA/TSRA MAY IMPACT KILG  
IN THE AFTERNOON, BUT CONFIDENCE IS LOW. WINDS SHIFT FROM W-SW  
TO NW LATE IN THE MORNING WITH THE PASSAGE OF A COLD FRONT AT  
8-12 KT WITH GUSTS UP TO 20 KT.  
 
OUTLOOK...  
 
TUESDAY NIGHT...GENERALLY VFR CONDITIONS EXPECTED.  
 
WEDNESDAY-WEDNESDAY NIGHT...GENERALLY VFR EARLY, MVFR  
CONDITIONS MAY DEVELOP LATER IN THE DAY INTO THE EVENING WITH A  
CHANCE OF SHOWERS.  
 
THURSDAY-FRIDAY NIGHT...GENERALLY VFR CONDITIONS EXPECTED.  
 
SATURDAY...MVFR CONDITIONS LIKELY TO DEVELOP AS A WARM FRONT  
APPROACHES AND LIFTS ACROSS THE AREA WITH A CHANCE OF SHOWERS.  
SOUTH TO SOUTHEAST WINDS MAY GUST 15-20 KNOTS DURING THE DAY.  
 

 
   
MARINE
 
 
SUB-SCA CONDITIONS. S WINDS 15-20 KT ON THE NJ OCEAN WATERS  
TONIGHT, BUT GUSTS TO 25 KT NOT EXPECTED. WINDS WILL DIMINISH  
THROUGH THE OVERNIGHT. SW WINDS BECOME NW TUESDAY MORNING  
BEHIND THE PASSAGE OF A COLD FRONT WITH WIND SPEEDS 10-15 KT  
WITH GUSTS UP TO 20 KT.  
 
SHOWERS AND THUNDERSTORMS MAY RESULT IN GUSTY WINDS, LIGHTNING,  
AND VSBY RESTRICTIONS IN HEAVY RAIN MAINLY DURING THE  
OVERNIGHT.  
 
RIP CURRENTS...  
 
ON TUESDAY, SEAS WILL AVERAGE 2-3 FEET WITH A DOMINANT PERIOD  
OF 6-7 SECONDS. THE RISK FOR THE DEVELOPMENT OF DANGEROUS RIP  
CURRENTS IS LOW FOR THE DELAWARE AND NEW JERSEY BEACHES.  
 
OUTLOOK...  
 
TUESDAY NIGHT-WEDNESDAY...CONDITIONS EXPECTED TO REMAIN BELOW  
ADVISORY LEVELS THROUGH WEDNESDAY.  
 
WEDNESDAY NIGHT...WINDS MAY INCREASE WEDNESDAY NIGHT AS AN AREA  
OF LOW PRESSURE MOVES OFF THE COAST AND OVER THE COASTAL  
WATERS. HOWEVER, CONDITIONS WILL LIKELY REMAIN BELOW ADVISORY  
LEVELS, ALTHOUGH WINDS MAY GUST AROUND 20 KNOTS AT TIMES. THERE  
IS A CHANCE OF SHOWERS AND THUNDERSTORMS WHICH COULD LEAD TO  
LOCALLY HIGHER WINDS AND WAVES.  
 
THURSDAY-FRIDAY NIGHT...CONDITIONS EXPECTED TO REMAIN BELOW  
ADVISORY LEVELS, BUT WINDS MAY GUST AROUND 20 KNOTS AT TIMES.  
 
SATURDAY...A WARM FRONT IS FORECAST TO LIFT NORTH OF THE AREA  
LATER SATURDAY INTO SATURDAY NIGHT. WINDS MAY GUST AROUND 20  
KNOTS AT TIMES, BUT ARE EXPECTED TO REMAIN BELOW ADVISORY  
LEVELS. THERE IS A CHANCE OF SHOWERS AND THUNDERSTORMS WHICH  
COULD LEAD TO LOCALLY HIGHER WINDS AND WAVES.  
 

 
   
CLIMATE
 
 
THE HIGH TEMPERATURE AT ALLENTOWN, PA REACHED 95 DEGREES TODAY.  
THIS TIED THE OLD RECORD PREVIOUSLY SET IN 1957.  
 

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

 
 

 
SYNOPSIS...ROBERTSON  
NEAR TERM...MPS  
SHORT TERM...FITZSIMMONS  
LONG TERM...ROBERTSON  
AVIATION...FITZSIMMONS/ROBERTSON/MPS  
MARINE...FITZSIMMONS/ROBERTSON/MPS  
CLIMATE...MPS  
 
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