128  
FXUS61 KPHI 221918  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
318 PM EDT FRI JUN 22 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE SITUATED EAST OF NEW ENGLAND WILL CONTINUE TO MOVE  
OFFSHORE TONIGHT. MEANWHILE, A LOW PRESSURE SYSTEM ORGANIZING OVER  
THE MISSISSIPPI VALLEY LEADS TO A WARM FRONTAL PASSAGE THROUGH THE  
REGION ON SATURDAY FOLLOWED BY A COLD FRONTAL PASSAGE LATE SUNDAY.  
HIGH PRESSURE OVER ONTARIO BUILDS INTO THE REGION ON MONDAY AND  
SLOWLY MOVES OFF THE EASTERN SEABOARD TO A POSITION NEAR BERMUDA BY  
THE END OF NEXT WEEK.  

 
 
   
NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
 
 
WEAK LOW PRESSURE AND A SLOW MOVING FRONT WILL APPROACH FROM THE S  
TONIGHT. FREQUENT SHOWERS ARE EXPECTED WITH THE SYSTEM AND SOME  
HEAVIER SHOWERS MAY OCCUR AFTER MIDNIGHT. A TSTM IS POSSIBLE ACROSS  
THE DELMARVA AREAS. WE WILL WORD THE FCST ACCORDINGLY. IT WILL  
REMAIN MILD AND HUMID OVERNIGHT WITH LOWS ONLY DROPPING INTO THE  
MID/UPPER 60S S/E AND UPPER 50S TO LOW 60S N/W. WINDS WILL REMAIN  
ONSHORE E/SE AT AROUND 10 MPH IN MOST AREAS. CLOSER TO THE SHORE,  
WINDS WILL BE 15 TO 20 MPH AT TIMES WITHS SOME GUSTS AROUND 25  
MPH.  

 
 
   
SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/
 
 
THE FRONT WILL MOVE NORTHWARDS ACROSS THE AREA DURING THE DAY. WHERE  
IT ENDS UP WILL DETERMINE WEATHER TYPES THROUGH THE DAY. AREAS S/E  
WILL LIKELY BREAK OUT INTO SOME SUNSHINE AFTER THE MORNING SHOWERS.  
THESE AREAS HAVE A BETTER CHC FOR REACHING HIGH TEMPS IN THE  
MID/UPPER 80S. ALSO, THESE S/E AREAS HAVE A BETTER CHC FOR AFTERNOON  
TSTMS WITH SOME HEAVY RAINS AND PSBL SVR WEATHER. THE SPC HAS A  
MARGINAL RISK FOR DAY2 ACROSS THE SRN HALF OF OUR CWA. WE HAVE  
INCLUDED THE DELAWARE VALLEY IN THESE (WESTERN/TSTM) AREAS ATTM, BUT  
THERE IS MORE THAN AVERAGE UNCERTAINTY WITH REGARDS TO THIS.  
 
FURTHER N/W, THE FRONT MAY NOT MOVE THRU AS THE LOW PASSES BY, SO  
PLENTY OF SHOWERS AND LOW CLOUDS MAY LINGER THROUGH THE DAY.  
TEMPERATURES IN THESE AREAS MAY REMAIN IN THE 70S ALL DAY WITH  
FREQUENT SHOWERS.  

 
 
   
LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/
 
 
SATURDAY NIGHT THROUGH MONDAY....  
 
TO START THE PERIOD SATURDAY EVENING, WARM FRONT WILL BE DRAPED OVER  
EASTERN PA EXTENDING EAST INTO CENTRAL NJ...LIKELY NEAR OR JUST  
NORTH OF PHILADELPHIA AND TRENTON. EXPECT THAT STRONG TO POTENTIALLY  
SEVERE THUNDERSTORMS MAY BE ONGOING INTO THE EARLY PART OF THE  
EVENING BEFORE MOVING OUT BY LATE EVENING. THE STRONGEST STORMS  
SHOULD BE NEAR AND SOUTH OF THE WARM FRONT WITH TORRENTIAL RAIN AND  
DAMAGING WINDS BEING THE BIGGEST THREATS. ONCE THESE HEAVIER  
SHOWERS/STORMS MOVE OUT BY THE OVERNIGHT THE AREA WILL REMAIN MUGGY  
AND MOIST WITH FAIRLY LIGHT WINDS AS THE DIFFUSE FRONT LINGERS OVER  
THE AREA. THERE COULD BE SOME SCATTERED TO ISOLATED SHOWERS BUT  
THESE WOULD BE FEW AND FAR BETWEEN. THE OTHER CONCERN WILL BE AREAS  
OF LOW CLOUDS AND PATCHY FOG, ESPECIALLY OVER THE HIGHER TERRAIN OF  
EASTERN PA , THAT MAY FORM OVERNIGHT IN THE WEAK, MOIST FLOW. LOWS  
SHOULD RANGE FROM THE LOW TO MID 60S NORTH TO THE LOW 70S SOUTH  
WHERE IT WILL ALSO FEEL ESPECIALLY MUGGY SINCE DEW POINTS WILL ALSO  
LINGER NEAR 70.  
 
FOR SUNDAY, DIFFUSE AREA OF LOW PRESSURE TRACKS EAST ACROSS UPSTATE  
NY TOWARD SW NEW ENGLAND THROUGH THE DAY DRAGGING A COLD FRONT  
TOWARD THE AREA BY LATE DAY. SINCE THE AREA WILL BE IN THE WARM  
SECTOR, EXPECT GENERALLY WARM TO HOT CONDITIONS UNDER VARIABLE  
CLOUDS WITH HIGHS MOSTLY IN THE 80S TO AS HIGH AS 90 OVER INTERIOR  
PORTIONS OF THE DELMARVA. AS MENTIONED, LATE DAY A COLD FRONT WILL  
APPROACH ALONG WITH AN ASSOCIATED UPPER LEVEL TROUGH AND THIS WILL  
RESULT IN SCATTERED SHOWERS/STORMS DEVELOPING ONCE AGAIN THROUGH THE  
AFTERNOON INTO THE EARLY EVENING...INITIALLY AFFECTING THE HIGHER  
TERRAIN AREAS OF EASTERN PA BUT POTENTIALLY AFFECTING THE COAST BY  
EVENING. CONDITIONS DON'T LOOK QUITE AS FAVORABLE FOR SEVERE WEATHER  
COMPARED TO SATURDAY BUT IT'S STILL POSSIBLE A FEW STORMS COULD  
PRODUCE LOCALLY STRONG TO MARGINALLY SEVERE WIND GUSTS AS THERE WILL  
SOME INSTABILITY (ML CAPES 500-1000 J/KG) WITH FAIRLY STEEP LOW  
LEVEL LAPSE RATES.  
 
SUNDAY NIGHT, SCATTERED SHOWERS/STORMS CONTINUE INTO THE EVENING AS  
THE COLD FRONT MOVES ACROSS BEFORE MOVING OUT OVERNIGHT. IT WILL BE  
ANOTHER FAIRLY MUGGY, MILD NIGHT WITH LOWS IN THE 60S TO NEAR  
70 THOUGH DEW POINTS WILL START TO FALL OVERNIGHT BEHIND THE FRONT.  
 
HEADING INTO MONDAY, SKIES CLEAR WITH HUMIDITY LEVELS CONTINUING TO  
FALL AS DRIER AIR CONTINUES TO BE USHERED IN BY NORTHERLY WINDS  
BEHIND THE FRONT. HIGHS WILL GENERALLY BE IN THE LOW TO MID 80S  
EXCEPT 70S IN THE FAR NORTH.  
 
MONDAY NIGHT THROUGH FRIDAY...  
 
HIGH PRESSURE MOVES IN AND DOMINATES OUR WEATHER MONDAY NIGHT  
THROUGH TUESDAY AND TUESDAY NIGHT BRINGING MAINLY CLEAR SKIES WITH  
SEASONABLE TEMPERATURES AND COMFORTABLE HUMIDITY LEVELS. BEYOND THIS  
TIME, FORECAST MODELS START TO DIVERGE IN SOME OF THE FORECAST  
DETAILS. FOR WEDNESDAY, THE HIGH MOVES OFF THE COAST SO TEMPERATURES  
AND ESPECIALLY DEW POINTS START TO CREEP UP. THE NEXT SYSTEM WILL  
BEGIN TO ADVANCE TOWARDS THE AREA WITH THE GFS BRINGING THIS SYSTEM  
IN FASTER THAN THE ECMWF AND GEM AS THESE MODELS HOLD IT OFF UNTIL  
THURSDAY. FOR THIS REASON, WE INTRODUCE POPS FOR SHOWERS/STORMS  
WEDNESDAY AFTERNOON BUT ONLY KEEP THEM AT SLIGHT CHANCE AND FOR  
AREAS MAINLY WEST OF THE I-95 CORRIDOR.  
 
HEADING TOWARDS THE END OF NEXT WEEK, EARLY INDICATIONS ARE FOR A  
FAIRLY STRONG RIDGE TO BUILD ACROSS THE WESTERN ATLANTIC EXTENDING  
WEST ALONG THE COAST...THOUGH THE GFS IS STRONGER THAN THE GEM AND  
ECMWF WITH THIS FEATURE. AS A RESULT, TEMPERATURES LOOK TO HEAT UP  
AND COULD POTENTIALLY REACH VALUES OF 90+ ALONG WITH INCREASING  
HUMIDITY. HOWEVER THERE WILL ALSO BE AN INCREASING CHANCE FOR  
SCATTERED AFTERNOON SHOWERS AND STORMS IN THE SW FLOW.  

 
 
   
AVIATION /19Z FRIDAY THROUGH WEDNESDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
REST OF AFTERNOON/EARLY EVENING...SHOWERS WITH CONDITIONS VARYING  
BETWEEN VFR AND HIGH END MVFR. WINDS MOSTLY E AT 10 TO 12 KNOTS WITH  
SOME GUSTS AROUND 20 KNOTS.  
 
TONIGHT...CIGS AND VSBYS DECREASE WITH OCCASIONAL SHOWERS AS A SLOW  
MOVING FRONT APPROACHES FROM THE SOUTH. MOST GUIDANCE HAS IFR CIGS  
DEVELOPING OVERNIGHT. WE DECIDED TO FOLLOW THIS SINCE WITH THE  
ONSHORE FLOW AND LOW LEVEL COOL/MOIST AIR, THIS LOOKS REASONABLE.  
 
SATURDAY...SLOW IMPROVEMENT FROM S TO N DURING THE MORNING. AREAS  
S/E MAY BREAK OUT TO VFR BY LATE MORNING WHILE THE DELAWARE VALLEY  
SITES MAY HAVE TO WAIT UNTIL LATER IN THE AFTERNOON. SCT TSTMS WILL  
DEVELOP IN THE AFTERNOON INSTABILITY S/E, POSSIBLY AFFECTING KPHL.  
CONFID IN FRONTAL PLACEMENT AND EXPECTED WEATHER IS LOW-MEDIUM FOR  
SATURDAY. WINDS BECOMING S TO SW BY AFTERNOON.  
 
OUTLOOK...  
 
SATURDAY NIGHT...TSRA POSSIBLE UNTIL 06Z. THEREAFTER, MVFR IN LOW  
CLOUDS AND PATCHY FOG POSSIBLE, MAINLY ABE, RDG, MIV, AND ACY.  
SOUTHWEST WINDS LESS THAN 10 KT. LOW CONFIDENCE.  
 
SUNDAY...MVFR IN LOW CLOUDS AND PATCHY FOG IMPROVING TO VFR EARLY.  
ANOTHER ROUND OF SHRA POSSIBLE AT ALL TERMINALS, WITH TSRA POSSIBLE  
AT TTN-ABE-RDG, MAY LEAD TO BRIEF CEILING/VISIBILITY RESTRICTIONS.  
WEST-SOUTHWEST WINDS AROUND 10 KT WITH GUSTS OF 15-20 KNOTS. MEDIUM  
CONFIDENCE.  
 
SUNDAY NIGHT...SPOTTY MVFR POSSIBLE DUE TO LOW CLOUDS AND SHRA,  
ESPECIALLY AT ABE AND RDG. OTHERWISE VFR. WINDS VEERING TO THE  
NORTHWEST AROUND 10 KT. LOW CONFIDENCE.  
 
MONDAY - TUESDAY...MVFR IN PATCHY FOG POSSIBLE MONDAY NIGHT INTO  
EARLY TUESDAY MORNING. OTHERWISE VFR. NORTHWEST WINDS AROUND 10 KT  
ON MONDAY BECOMING LIGHT AND VARIABLE MONDAY NIGHT INTO TUESDAY.  
 
WEDNESDAY...MAINLY VFR.  

 
 
   
MARINE
 
 
TONIGHT...SCA CONDITIONS EXPECTED WITH OCCASIONAL SHOWERS. A FEW  
TSTMS POSSIBLE ACROSS THE DELAWARE COASTAL OR SRN NJ COASTAL WATERS  
AFTER MIDNIGHT.  
 
SATURDAY...SCA CONDITIONS THE FIRST PART OF THE DAY, THEN  
DECREASING WINDS AND SEAS. SHOWERS EXPECTED DURING THE MORNING,  
THE SCT TSTMS WILL BE AROUND FOR THE AFTERNOON. LOCALLY HIGHER  
WINDS AND SEAS WITH ANY TSTM.  
 
OUTLOOK...  
 
STRONG THUNDERSTORMS WILL BE POSSIBLE OVER THE WATERS INTO SATURDAY  
EVENING AND MAY BRING LOCAL WIND GUSTS TO 34+ KNOTS. THESE ARE  
EXPECTED TO WEAKEN AND MOVE OUT BY THE OVERNIGHT WITH OTHERWISE  
BREEZY SW WINDS CONTINUING SATURDAY NIGHT AND SUNDAY THOUGH WINDS  
SHOULD REMAIN BELOW SCA LEVELS. HOWEVER SATURDAY NIGHT INTO EARLY  
SUNDAY, SEAS MAY REACH THE 4-6 FT RANGE.  
 
BY LATE DAY SUNDAY INTO SUNDAY NIGHT, ADDITIONAL SHOWERS AND STORMS  
WILL BE POSSIBLE AS A COLD FRONT MOVES THROUGH WITH WINDS SHIFTING  
TO NORTHERLY BEHIND THE FRONT FOR MONDAY. EXPECT CONDITIONS TO BELOW  
SCA LEVELS DURING THIS PERIOD. BEYOND THIS TIME, HIGH PRESSURE  
BUILDS OVER THE WATERS MONDAY NIGHT THROUGH TUESDAY BRINGING LIGHT  
WINDS WITH SEAS GENERALLY 3 FT OR LESS. THIS HIGH MOVES EAST OF THE  
WATERS BY WEDNESDAY WITH SW WINDS AS WELL AS SEAS STARTING TO RAMP  
UP ONCE AGAIN, POTENTIALLY TO NEAR SCA LEVELS BY LATE DAY.  

 
 
   
TIDES/COASTAL FLOODING
 
 
WITH A PERSISTENT ONSHORE FLOW THROUGH EARLY SATURDAY,  
INCREASINGLY POSITIVE DEPARTURES FROM ASTRONOMICAL TIDES ARE  
EXPECTED. THE HIGH TIDE OF MOST CONCERN IS TONIGHT, WHEN MINOR  
FLOODING IS POSSIBLE IN SPOTS.  

 
 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 2 PM EDT SATURDAY FOR ANZ431-  
451>455.  
SMALL CRAFT ADVISORY FROM 2 AM TO 2 PM EDT SATURDAY FOR ANZ450.  
 

 
 

 
SYNOPSIS...FITZSIMMONS  
NEAR TERM...O'HARA  
SHORT TERM...O'HARA  
LONG TERM...FITZSIMMONS  
AVIATION...FITZSIMMONS/O'HARA  
MARINE...FITZSIMMONS/O'HARA  
TIDES/COASTAL FLOODING...  
 
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