519  
FXUS61 KPHI 182032  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
432 PM EDT THU JUL 18 2019  
   
SYNOPSIS
 
 
A WEAK WAVE OF LOW PRESSURE WILL DRIFT OUT TO SEA BY FRIDAY MORNING.  
A STRONG RIDGE OF HIGH PRESSURE WILL BUILD OVER THE REGION FROM  
FRIDAY THROUGH THE WEEKEND. AN EXTENDED PERIOD OF EXCESSIVE HEAT IS  
EXPECTED. A STRONG AND SLOW MOVING COLD FRONT WILL APPROACH BY  
MONDAY. THIS FRONT WILL LIKELY MOVE OFFSHORE BY TUESDAY. HIGH  
PRESSURE WITH DRY AND MUCH COOLER WEATHER SHOULD BUILD IN FROM THE  
WEST BY THE MIDDLE OF NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
 
 
SHOWERS AND TSTMS CONTINUE TO DEVELOP ACROSS MUCH OF THE AREA AS  
WEAK LOW PRESSURE PASSES THE AREA. THE WARM AND HUMID AIR MASS IN  
PLACE AND WEAK DYNAMICS ARE SUFFICIENT FOR THE STORM FORMATION. THE  
TSTMS ARE PRODUCING EXCESSIVE RAINFALL IN SOME AREAS, SO FFWS HAVE  
BEEN ISSUES FOR SOME AREAS. THE THREAT FOR SEVERE WEATHER LOOKS LOW,  
BUT STILL BE PREPARED FOR THE POSSIBILITY OF HAZARDOUS WEATHER SINCE  
A STRONG WIND GUST OR TWO FROM TSTMS CAN'T BE RULED OUT.  
 
THESE SHOWERS AND TSTMS ACROSS THE REGION WILL END FROM NW TO SE  
THIS EVENING AND EARLY TONIGHT. IT WILL REMAIN WARM AND HUMID  
OVERNIGHT. LOW CLOUDS AND FOG WILL ONCE AGAIN DEVELOP. WINDS WILL BE  
LIGHT FROM THE N LATER TONIGHT.  
 

 
   
SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/
 
 
A DRY DAY IS EXPECTED BY-IN-LARGE, HOLDING ONLY A SLIGHT CHC FOR AN  
AFTERNOON SHOWER ACROSS THE SOUTHERN POCONOS. HOT AND HUMID  
CONDITIONS EXPECTED AFTER THE MORNING LOW CLOUDS AND PATCHY FOG BURN  
OFF. HIGHS WILL BE IN THE MID/UPPER 90S EVERYWHERE EXCEPT AT THE  
SHORE AND ACROSS THE HIGHER ELEVATIONS OF THE SOUTHERN POCONOS.  
HIGHS IN THOSE AREAS WILL BE MORE LIKE UPPER 80S TO LOW 90S. AN  
EXCESSIVE HEAT WARNING WILL BE ISSUED FOR ALL AREAS OF THE CWA  
BEGINNING FRIDAY.  
 

 
   
LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/
 
 
OVERVIEW...  
 
ALL INDICATIONS REMAIN ON TRACK FOR A PROLONGED, DANGEROUS, AND  
POTENTIALLY DEADLY PERIOD OF EXCESSIVE HEAT FOR OUR AREA OVER THE  
WEEKEND. AN EXPANSIVE RIDGE EXTENDING FROM THE SOUTH CENTRAL STATES  
OUT INTO THE WESTERN ATLANTIC WILL YIELD NEAR RECORD WARMTH FOR  
MULTIPLE DAYS. SATURDAY AND SUNDAY WILL BOTH SEE HEAT INDICES IN  
EXCESS OF 100 DEGREES, POTENTIALLY AS HIGH AS 115 DEGREES ON  
SATURDAY. HEAT RELATED ILLNESSES AND DEATH CAN OCCUR IN MINUTES ON  
DAYS SUCH AS THESE IN CASES OF OVER-EXERTION OR ENTRAPMENTS IN HOT  
VEHICLES. BECAUSE OF THIS, EXTREME CAUTION SHOULD BE EXERCISED OVER  
THE WEEKEND WITH REGARDS TO THE HEAT.  
 
A COLD FRONT, SIGNALING A PATTERN CHANGE, WILL SLOWLY APPROACH BY  
MONDAY. DURING THE AIR MASS TRANSITION, A PERIOD OF HEAVY RAINFALL  
IS POSSIBLE. BY THE MIDDLE OF NEXT WEEK, AN ENTIRELY DIFFERENT  
PATTERN TAKES SHAPE OVER THE CONUS. AFTER THE FRONTAL PASSAGE MONDAY  
NIGHT OR TUESDAY, A ROBUST TROUGH DIGS IN OVER THE EAST, WITH STRONG  
RIDGING OVER THE MOUNTAIN WEST. THIS WILL YIELD MUCH COOLER AND  
DRIER WEATHER AS WE HEAD TOWARDS THE MIDDLE OF NEXT WEEK, BRINGING  
WELCOME RELIEF FROM THE HEAT.  
 
DAILIES...  
 
FRIDAY NIGHT... A VERY WARM NIGHT WITH LOWS IN THE MID TO UPPER 70S,  
AROUND 80 IN THE URBAN CORRIDOR. SOME GUIDANCE IS INDICATING THE  
POTENTIAL FOR AN MCS TO TRACK OVER NORTHERN OR CENTRAL PORTIONS OF  
THE AREA AS A SHORTWAVE MOVES THROUGH. AS IS TYPICAL OF SUCH EVENTS,  
AGREEMENT IN GUIDANCE IS VERY POOR, AND SEVERAL MODELS SHOW NOTHING  
AT ALL. KEPT POPS LOW FOR NOW, BUT WILL CONTINUE TO MONITOR IN THE  
EVENT THIS IDEA STARTS TO GAIN ANY TRACTION.  
 
SATURDAY-SUNDAY... BLISTERING HEAT. NO SIGNIFICANT CHANGES IN TERMS  
OF THE TEMPERATURE FORECASTS. SATURDAY'S HIGHS WERE NUDGED DOWN JUST  
A DEGREE OR TWO, WITH SUNDAY'S INCHED UP A DEGREE OR SO. THE RESULT  
IS BOTH DAYS NOW LOOK TO HAVE VERY SIMILAR HIGH TEMPERATURES, THOUGH  
SATURDAY STILL HAS THE HIGHEST HEAT INDICES, UP TO 115 IN THE URBAN  
CORRIDOR BUT WITH WIDESPREAD VALUES OVER 105. THESE HEAT INDEX  
VALUES COME DOWN ABOUT 5 DEGREES SUNDAY BUT REMAIN IN VERY DANGEROUS  
TERRITORY, AROUND 100 TO 110. IN ADDITION, ANOTHER IMPORTANT  
CONSIDERATION IS THE OVERNIGHT MINIMUMS, ESPECIALLY SATURDAY NIGHT  
WHEN MOST PLACES WON'T FALL BELOW THE MID 70S AND SOME URBAN AREAS  
WILL NOT GO BELOW 80. THIS WILL MAKE FOR VERY LITTLE OVERNIGHT  
RELIEF. WAS NOT GOING TO QUIBBLE ON HEADLINES; WENT WITH A BLANKET  
EXCESSIVE HEAT WARNING FOR ALL AREAS THROUGH SUNDAY. SATURDAY LOOKS  
TO STAY DRY THOUGH CANNOT COMPLETELY RULE OUT A POP-UP STORM  
ESPECIALLY TO THE WEST. BY SUNDAY, SHOWERS AND THUNDERSTORMS MAY  
APPROACH FROM THE WEST AS A FRONT BEGINS MOVING TOWARDS THE AREA,  
THOUGH THERE ARE SOME INDICATIONS THIS MAY HOLD OFF UNTIL LATER.  
GIVEN HIGH HEAT AND HUMIDITY, ANY STORMS COULD PRODUCE LOCALLY HEAVY  
RAINFALL.  
 
SUNDAY NIGHT-MONDAY NIGHT... THIS WILL BE OUR TRANSITION PERIOD. A  
STRONG BUT SLOW MOVING COLD FRONT WILL BE APPROACHING FROM THE WEST.  
THE AIR MASS AHEAD OF IT WILL BE VERY MOIST, WITH PWATS COMING BACK  
UP TO AROUND 2.25" OR HIGHER AFTER EASING BACK A LITTLE ON SUNDAY.  
AS THE FRONT CRAWLS THROUGH, IT LOOKS LIKE ONE OR MORE WAVES OF LOW  
PRESSURE MAY DEVELOP ALONG IT. THERE IS DEFINITELY A RISK FOR HEAVY  
RAINFALL AND FLASH FLOODING OVER THIS PERIOD ESPECIALLY IF WE DO GET  
MULTIPLE ROUNDS OF CONVECTION AS NEW WAVES OF LOW PRESSURE DEVELOP.  
IN ADDITION, GIVEN THE TROPICAL AIR MASS EXPECTED MONDAY, IT IS  
POSSIBLE IF NOT LIKELY THAT SOME NEW HEAT HEADLINES WILL BE NEEDED,  
THOUGH CLOUD COVER WILL KEEP THE HIGHS ABOUT 10 DEGREES COOLER THAN  
SUNDAY. DEPENDING ON THE SPEED OF THE FRONT, COOLER AIR MAY START TO  
FILTER IN BY MONDAY NIGHT.  
 
TUESDAY-THURSDAY... WELCOME RELIEF. A MUCH COOLER, MUCH DRIER AIR  
MASS SETTLES IN. A LINGERING SHOWER IS POSSIBLE TUESDAY ESPECIALLY  
OVER DELMARVA AND COASTAL NJ. OTHERWISE, MOST OF THIS PERIOD SHOULD  
BE DRY, THOUGH AN AFTERNOON SHOWER OR STORM IS POSSIBLE BY THURSDAY  
AS AN UPPER LEVEL DISTURBANCE APPROACHES. HIGHS GENERALLY IN THE LOW  
TO MID 80S WITH COMFORTABLE DEW POINTS, SO THIS LOOKS LIKE A REALLY  
NICE STRETCH, CERTAINLY COMPARED TO THE ONGOING HEAT.  
 

 
   
AVIATION /21Z THURSDAY THROUGH TUESDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
REST OF THE AFTERNOON...SCATTERED SHOWERS AND TSTMS WILL DIMINISH  
FROM W TO E INTO THE EVENING. MVFR/IFR POSSIBLE IF ACTIVITY MOVES  
DIRECTLY ACROSS TERMINAL, LIMITED CONFID. LIGHT AND VARIABLE WINDS.  
 
TONIGHT...VFR, THEN LOW CLOUDS AND AREAS OF FOG WILL DEVELOP  
OVERNIGHT. WIDESPREAD MVFR EXPECTED WITH IFR POSSIBLE. LIGHT WINDS  
 
FRIDAY...LOW CLOUDS AND ANY FOG DIMINISH 13Z/14Z THEN VFR EXPECTED  
WITH SOME SCT DAYTIME CU. MOSTLY N OR NW WINDS 5 TO 10 KNOTS.  
 
OUTLOOK...  
 
FRIDAY NIGHT-SATURDAY NIGHT... GENERALLY VFR. MVFR IS POSSIBLE DUE  
TO VISIBILITY RESTRICTIONS IN HAZE ON SATURDAY. WEST-SOUTHWEST WIND  
5 TO 10 KT.  
 
SUNDAY... MAINLY VFR BUT MVFR POSSIBLE IN HAZE. AFTERNOON AND  
EVENING SHOWERS AND THUNDERSTORMS POSSIBLE ESPECIALLY NEAR AND WEST  
OF PHL. WESTERLY WIND 5 TO 10 KT.  
 
SUNDAY NIGHT-MONDAY NIGHT... WIDESPREAD SHOWERS AND THUNDERSTORMS  
WITH ASSOCIATED MVFR AND IFR CONDITIONS. WESTERLY WINDS BECOMING  
NORTHWESTERLY AT 5 TO 10 KT.  
 
TUESDAY... LINGERING MVFR POSSIBLE EARLY, BUT SHOULD TREND VFR  
WITH A LIGHT NORTH OR NORTHEAST WIND.  
 

 
   
MARINE
 
 
TONIGHT...A CONTINUATION OF SUB-SCA CONDITIONS WITH  
SCATTERED TSTMS THIS EVENING AND THEN SOME PATCHY FOG OVERNIGHT.  
WINDS WILL BE MOSTLY SW OR W AT 5 TO 10 KNOTS. SEAS MOSTLY  
AROUND 3 FT. WINDS AND SEAS HIGHER IN TSTMS.  
 
FRIDAY...WINDS WILL BE RATHER LIGHT AND VARIABLE EARLY, THEN SWITCH  
AROUND TO SW DURING THE AFTERNOON AND INCREASE TO AROUND 10 KNOTS.  
SEAS WILL BE MAINLY 2 TO 3 FT.  
 
OUTLOOK...  
 
WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA THROUGH THE  
PERIOD.  
 
RIP CURRENTS...  
 
LOW RISK OR DANGEROUS RIP CURRENTS WILL CONTINUE THE REST OF  
TODAY.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...EXCESSIVE HEAT WARNING FROM NOON FRIDAY TO 10 PM EDT SUNDAY  
FOR PAZ054-055-060>062-101-103-105.  
EXCESSIVE HEAT WARNING UNTIL 10 PM EDT SUNDAY FOR PAZ070-071-  
102-104-106.  
NJ...EXCESSIVE HEAT WARNING FROM NOON FRIDAY TO 10 PM EDT SUNDAY  
FOR NJZ001-007>010-012>014-016-020>027.  
EXCESSIVE HEAT WARNING UNTIL 10 PM EDT SUNDAY FOR NJZ015-  
017>019.  
DE...EXCESSIVE HEAT WARNING FROM NOON FRIDAY TO 10 PM EDT SUNDAY  
FOR DEZ002>004.  
EXCESSIVE HEAT WARNING UNTIL 10 PM EDT SUNDAY FOR DEZ001.  
MD...EXCESSIVE HEAT WARNING FROM NOON FRIDAY TO 10 PM EDT SUNDAY  
FOR MDZ008-012-015-019-020.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...O'BRIEN  
NEAR TERM...O'HARA  
SHORT TERM...O'HARA  
LONG TERM...O'BRIEN  
AVIATION...O'BRIEN/O'HARA  
MARINE...O'BRIEN/O'HARA  
 
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