108  
FXUS61 KPHI 262009  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
409 PM EDT WED JUL 26 2017  
   
SYNOPSIS
 
 
HIGH PRESSURE ACROSS THE NORTHEAST WILL MOVE OFFSHORE TONIGHT. A  
COLD FRONT WILL APPROACH THE REGION ON THURSDAY BEFORE DISSIPATING.  
A WARM FRONT WILL MOVE NORTHWARD INTO THE REGION LATE THURSDAY. LOW  
PRESSURE WILL FORM ALONG THE FRONTAL BOUNDARY, MOVING THROUGH OUR  
AREA ON FRIDAY AND SATURDAY. HIGH PRESSURE WILL THEN RETURN LATER  
SATURDAY AND PERSIST THROUGH TUESDAY. ANOTHER COLD FRONT WILL  
APPROACH THE REGION ON TUESDAY OR WEDNESDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
 
 
HIGH PRESSURE CENTERED OVER THE NORTHEAST WILL CONTINUE TO DRIFT  
OFFSHORE THIS EVENING. MEANWHILE, DEVELOPING AND STRENGTHENING LOW  
PRESSURE OVER THE MIDWEST WILL BEGIN TO PUSH EAST. A WARM FRONT OUT  
AHEAD OF THAT LOW WILL LIFT TOWARDS THE APPALACHIANS BY DAYBREAK  
THURSDAY.  
 
FOR THIS EVENING, SKIES WILL CLEAR OUT AS DIURNALLY DRIVEN STRATOCU  
WILL DISSIPATE SHORTLY AFTER SUNSET WITH LOSS OF DIURNAL HEATING.  
THIS WILL YIELD MAINLY CLEAR SKIES THROUGH MIDNIGHT OR SO. WITH A  
WEAK PRESSURE GRADIENT DUE TO THE HIGH MOVING OFFSHORE, CAN EXPECT A  
LIGHT SOUTHEAST FLOW (LESS THAN 5 MPH) TO CALM WINDS THROUGHOUT THE  
FORECAST AREA. THIS COMBINATION WILL RESULT IN FAIRLY DECENT  
RADIATIONAL COOLING CONDITIONS FOR THIS TIME OF YEAR FOR THE COASTAL  
PLAIN AND THE POCONO MOUNTAINS. WITH THE ONSHORE COMPONENT TO THE  
WINDS, HOWEVER, THIS RESULTS IN SURFACE MOISTURE INCREASING ACROSS  
MUCH OF NJ, SOUTHEAST PA, AND THE DELMARVA WITH DEWPOINTS SLOWLY  
CLIMBING UP THROUGH THE LOW TO MID 60S.  
 
IN THE FAVORED RADIATIONAL COOLING AREAS, CAN EXPECT RADIATIONAL  
FOG, STRATUS, AND POSSIBLE DRIZZLE TO DEVELOP AFTER MIDNIGHT TONIGHT  
AS AIR TEMPS FALL CLOSE TO THE DEWPOINT.  
 
LOWS TONIGHT WILL FALL INTO THE UPPER 50S TO LOW 60S IN THE POCONOS,  
NORTHWEST NJ, THE COASTAL PLAIN, AND THE DELMARVA, AND IN THE MID TO  
UPPER 60S IN THE LEHIGH AND DELAWARE VALLEYS.  
 

 
   
SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/
 
 
LOW PRESSURE MOVES INTO THE OHIO VALLEY ON THURSDAY. THE WARM FRONT  
OUT AHEAD OF THE LOW WILL LIFT INTO THE LEHIGH VALLEY AND POCONO  
MOUNTAINS THURSDAY MORNING, AND THERE MAY BE JUST ENOUGH LIFT TO  
TOUCH OFF A FEW SHOWERS WITH ITS APPROACH. WILL CAP POPS AT SLIGHT  
CHANCE FOR AREAS WEST OF THE FALL LINE. ANY SHOWERS THAT DEVELOP  
SHOULD TAPER OFF BY LATE THURSDAY MORNING.  
 
OTHERWISE, WARM FRONT CONTINUES ITS EASTWARD APPROACH THROUGHOUT THE  
DAY, AND SEEMS TO GET HUNG UP ACROSS SOUTHERN NJ BY LATE AFTERNOON.  
LATEST MODELS ARE FAIRLY CONSISTENT IN HOLDING OFF ON BULK OF PRECIP  
UNTIL LATE IN THE DAY, SO WILL ADJUST HOURLY POP GRIDS TO HOLD OFF  
ON THE HIGHER POPS UNTIL AFTER 4PM-5PM. WITH SB CAPE VALUES OF 1000-  
1500 J/KG EXPECTED ACROSS THE REGION, THERE SHOULD BE ENOUGH  
INSTABILITY FOR CONVECTION. THE QUESTION WILL BE IF ANY CONVECTION  
WILL BE STRONG ENOUGH TO OVERCOME ANY CAPPING INVERSIONS SHOWN ON  
BUFKIT SOUNDING PROFILES AT 800-700 MB. WILL KEEP POPS AND THUNDER  
CHANCES CAPPED AT CHANCE THROUGH 7PM.  
 
A WARM AND INCREASINGLY HUMID DAY ON TAP WITH HIGHER GENERALLY IN  
THE LOW TO MID 80S AND DEWPOINTS RISING INTO THE 60S/LOW 70S.  
 

 
   
LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/
 
 
UNSETTLED, WET WEATHER WILL AFFECT THE REGION FROM THURSDAY NIGHT  
THROUGH MUCH OF SATURDAY BEFORE WE SEE A COUPLE OF DRY DAYS FROM  
SUNDAY THROUGH THE EARLY PART OF NEXT WEEK.  
 
THURSDAY NIGHT STARTS WITH A STRONG UPPER LEVEL SHORTWAVE MOVING  
THROUGH THE REGION. AT THE SURFACE, A WEAK COLD FRONT DISSIPATES AS  
IT MOVES INTO THE AREA WHILE A WARM FRONT START TO PUSH NORTHWARD  
INTO THE REGION. LIMITED INSTABILITY DOES EXIST AS THE SHORTWAVE  
CROSSES THE REGION SO THERE IS THE POTENTIAL FOR THUNDERSTORMS TO  
DEVELOP AND SOME MAY BECOME SEVERE. SPC HAS LOWERED THE SEVERE RISK  
FOR THURSDAY NIGHT TO MARGINAL.  
 
FRIDAY WILL BE THE DAY WHEN THE RAINS MOVE INTO THE AREA. LOW  
PRESSURE WILL FORM ALONG THE FRONTAL BOUNDARY AND TRAVELS ALONG IT  
AND INTO OUR AREA ON FRIDAY. PWATS WILL INCREASE IN THE SOUTHERLY  
FLOW AND  
 
THE BIGGEST THREAT FROM THURSDAY NIGHT THROUGH SATURDAY LOOKS TO BE  
MAINLY FROM HEAVY RAIN. ANTECEDENT CONDITIONS ARE EXTREMELY WET AND  
THE GROUND IS NOT ABLE TO DO MUCH MORE THAN CREATE RUNOFF IN MANY  
AREAS ACROSS OUR FORECAST AREA. PRECIPITABLE WATER VALUES WILL ONCE  
AGAIN RISE TO 1.5-2.0 INCHES AND IT IS BECOMING MUCH CLEARER THAT  
PARTS OF THE AREA WILL SEE DECENT RAINFALL THROUGH SATURDAY. MODELS  
CONTINUE TO SHOW A SOLID SWATH OF 2-4 INCHES OF RAIN AROUND THE I-  
195 CORRIDOR TO I-95 AND POINTS TO THE SOUTH AND EAST, WITH 1 TO 2  
INCHES POSSIBLE ACROSS THE NORTHERN AND WESTERN AREAS. HELD OFF ON  
ISSUING ANY KIND OF FLASH FLOOD OR FLOOD WATCH AT THIS TIME DUE TO  
TIMING AND LOCATION UNCERTAINTIES BUT ONE WILL NEED TO BE  
CONSIDERED, MAINLY FOR FRIDAY INTO SATURDAY. NOT AS SOLD ON  
CONVECTION FOR FRIDAY BUT AGAIN, SOME INSTABILITY IS PRESENT AND  
SOME THUNDERSTORMS MAY DEVELOP ACROSS THE REGION. INCREASED RAINFALL  
TOTALS WILL BE POSSIBLE WHEREVER THUNDERSTORMS DEVELOP.  
 
THE LOW DEEPENS AND PICKS UP SPEED AS IT MOVES TO THE NORTHEAST ON  
SATURDAY. STRONG, GUSTY WINDS, ESPECIALLY ALONG THE COAST, WILL BE  
POSSIBLE. HOWEVER, WE SHOULD SEE CONDITIONS IMPROVE BY THE AFTERNOON  
HOURS AS HIGH PRESSURE SPREADS INTO THE REGION. WITH A DECENT  
NORTHERLY FLOW, TEMPERATURES WILL REMAIN COOLER ACROSS THE REGION,  
STRUGGLING TO REACH 80 ACROSS MUCH OF THE REGION.  
 
QUIET WEATHER WILL CONTINUE FOR SUNDAY THROUGH WEDNESDAY AS THE HIGH  
REMAINS IN CONTROL. A COLD FRONT MAY APPROACH THE REGION ON TUESDAY  
OR WEDNESDAY BUT IT LOOKS LIKE WE MIGHT HAVE LIMITED MOISTURE WITH  
IT AND HAVE KEPT THE FORECAST DRY FOR NOW.  
 

 
   
AVIATION /20Z WEDNESDAY THROUGH MONDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
LOW CLOUDS HARD TO SCOUR OUT, AND MVFR CIGS OF 2500-3000 FEET MAY  
PERSIST THROUGH SUNSET. OTHERWISE, STRATOCU DECK DISSIPATES AFTER  
SUNSET WITH LOSS OF DIURNAL HEATING.  
 
WITH INCREASING LOW LEVEL MOISTURE THROUGH THE NIGHT, MVFR CIGS IN  
STRATUS AND MVFR VSBYS IN BR/DZ LIKELY FOR TERMINALS AWAY FROM THE I-  
95 CORRIDOR, THOUGH MVFR CONDITIONS POSSIBLE AT KTTN. KEPT KTTN,  
KPHL, KPNE, AND KILG VFR WITH 18Z TAFS.  
 
CONDITIONS OTHERWISE GRADUALLY IMPROVE TO VFR ON FRIDAY, BUT  
PROBABLY NOT UNTIL AFTER 16Z  
 
LGT/VRB WINDS BECOME S-SW 5-7 KT LATE THURSDAY MORNING.  
 
OUTLOOK...  
 
THURSDAY NIGHT THRU SATURDAY...PERIODS OF MVFR/IFR CONDITIONS IN  
SHOWERS AND THUNDERSTORMS. STRONG NORTHEAST WINDS ON SATURDAY WITH  
GUSTS UP TO 25 KNOTS POSSIBLE, ESPECIALLY AT KACY.  
 
SATURDAY NIGHT THRU MONDAY...MAINLY VFR CONDITIONS EXPECTED.  
 

 
   
MARINE
 
 
WINDS AND SEAS WILL REMAIN BELOW SCA THRESHOLDS TONIGHT THROUGH  
THURSDAY. SEAS ARE AROUND 3 TO 4 FEET ON THE OCEAN WITH ONSHORE  
WINDS AROUND 10 TO 15 KNOTS.  
 
OUTLOOK...  
 
THURSDAY THRU FRIDAY...SUB-SCA CONDITIONS EXPECTED. LOCALLY HIGHER  
SEAS AND GUSTY WINDS IN THE VICINITY OF THUNDERSTORMS THROUGH FRIDAY  
NIGHT.  
 
SATURDAY AND SUNDAY...BOTH SEAS AND WINDS WILL INCREASE AS LOW  
PRESSURE DEEPENS ALONG THE MID-ATLANTIC COAST. A SMALL CRAFT  
ADVISORY WILL LIKELY BE NEEDED. GALE FORCE GUSTS POSSIBLE ON  
SATURDAY.  
 
SUNDAY NIGHT THROUGH MONDAY...SUB-SCA CONDITIONS ARE EXPECTED.  
 
RIP CURRENTS...  
 
WITH ONSHORE FLOW AND WAVES IN THE SURF ZONE AROUND 3 FEET, THERE IS  
A MODERATE RISK FOR THE DEVELOPMENT OF DANGEROUS RIP CURRENTS AT ALL  
BEACHES THROUGH THIS EVENING.  
 
A MODERATE RISK MAY BE IN PLACE ON THURSDAY AS WELL.  
 

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

 
 

 
SYNOPSIS...MEOLA  
NEAR TERM...MPS  
SHORT TERM...MPS  
LONG TERM...MEOLA  
AVIATION...MEOLA/MPS  
MARINE...MEOLA/MPS  
 
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