451  
FXUS61 KPHI 032004  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
404 PM EDT MON AUG 3 2015  
   
SYNOPSIS
 
 
A COLD FRONT FROM THE GREAT LAKES WILL SLOWLY APPROACH FROM THE  
NORTHWEST TONIGHT, EVENTUALLY TRACKING THROUGH OUR REGION ON  
TUESDAY. THIS FRONT IS FORECAST TO STALL JUST SOUTH OF OUR AREA  
THROUGH THE END OF THE WEEK WITH WAVES OF LOW PRESSURE MOVING ALONG  
IT. THE FINAL WAVE OF LOW PRESSURE LOOKS TO PASS OFFSHORE  
SOUTHEAST OF THE REGION ON SATURDAY. A HIGH PRESSURE SYSTEM FROM  
EASTERN CANADA SHOULD THEN BUILD SOUTHWARD ON SUNDAY AND MONDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
 
 
NOT A BAD AUGUST AFTERNOON WHERE HEAT INDEX TEMPS ARE PRETTY MUCH  
THE SAME AS THE AMBIENT TEMPS. THE EXCEPTION IS ACROSS OUR SOUTHERN  
ZONES WHERE DEWPOINTS ARE HIGHER. NORTH OF THE DELMARVA, DEWPOINTS  
ARE IN THE UPPER 50S TO LOWER 60S.  
 
TONIGHT'S LOWS WILL BOTTOM OUT IN THE LOWER 60S ACROSS THE FAR NORTH  
AND IN THE LOWER TO MID 70S ACROSS THE MID AND SOUTHERN ZONES. THIS  
IS WARMER THAN LAST NIGHT.  
 
A PREFRONTAL TROF OR REMNANT OUTFLOW BOUNDARY HAS BEEN WORKING  
ACROSS CENTRAL AND EASTERN PA THIS AFTERNOON. IT'S NOT RUNNING INTO  
A HIGHLY BUOYANT OR MOIST ATMOSPHERE, SO IT'S HAVING A TOUGH TIME  
GETTING GOING. THE ACTUAL COLD FRONT WILL PASS LATE TONIGHT INTO  
TOMORROW.  
 
WE'LL SLOWLY BUMP UP POPS FROM WEST TO EAST THIS EVENING INTO THE  
OVERNIGHT, BUT KEEP THE EXTREME FAR SOUTHERN AND EASTERN ZONES DRY.  
HIGHEST POPS (50%) WILL BE PLACED ACROSS THE POCONOS. 30% POPS HAVE  
PAINTED ACROSS THE DELAWARE VALLEY AND PORTIONS OF THE COASTAL  
PLAIN.  
 
THE GUSTY SOUTHWEST WINDS WE'RE EXPERIENCING THIS AFTERNOON WILL  
DIMINISH OVERNIGHT.  
 

 
   
SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/
 
 
FRONT GETS HUNG UP ALONG THE COAST TOMORROW. WITH SOME ADDITIONAL  
MOISTURE (VS. TODAY) POOLING NEAR THE FRONT AND A SHORTWAVE IN THE  
AREA, THE THINKING IS THAT SHOWERS AND THUNDERSTORMS COULD BE MORE  
NUMEROUS TOMORROW ACROSS THE EASTERN ZONES. THERE'S A SIGNIFICANT  
DIFFERENCE BETWEEN THE NAM AND GFS WITH THE NAM MUCH FURTHER WEST  
WITH PRECIP. I'VE CHOSEN TO GO CLOSER TO THE GFS WITH SUPPORT  
FROM STAT GUIDANCE.  
 
TEMPS TOMORROW, OVERALL, SHOULD BE A COUPLE DEGREES COOLER THAN  
TODAY'S HIGH. FORECASTING 90 FOR PHILLY.  
 
WINDS WILL BE A BIT MORE WESTERLY TOMORROW AFTERNOON WITH SIMILAR  
GUSTS VS. TODAY.  
 

 
   
LONG TERM /TUESDAY NIGHT THROUGH MONDAY/
 
 
IN A MODEL INITIALIZATION FLIP FROM THE WEEKEND, THE WRF/NAM  
INITIALIZED THE 500MB PATTERN BETTER THAN THE GFS OR ECMWF IN THE  
WESTERN CONUS, WHILE IN ERN NOAM THE GFS LOOKED BETTER. THE GFS  
LOOKED CLOSER AT 850 MB AND 925MB. DP/DTING THE INITIALIZATION  
OVER THE PAST 24 HOURS, THE RIDGING IN MONTANA AND IDAHO IS  
STRONGER AND DOWN THE ROAD THIS IS LEADING TO A MORE BIFURCATED  
SOLUTION TO HOW THE ENERGY ROUNDS THIS RIDGE, THUS THERE IS NO  
DECREASE IN UNCERTAINTY WITH THIS SOUNDING RUN. THE GFS WAS NOT  
USED BECAUSE OF ITS WEAKER WESTERN CONUS INITIALIZATION AND POOR  
RUN TO RUN CONTINUITY. GEFS MEAN WITH THE WAVE OF LOW PRESSURE IS  
FARTHER SOUTH AND THEN A FASTER EXIT ON SATURDAY. OUR FORECAST IS  
CLOSEST TO A ECMWF/CAN GGEM/MF-ARPEGE BLEND. IT SHOULD BE NOTED  
THAT THE UKMET HAS TRENDED SOUTHWARD WITH A MUCH WEAKER LOW WHILE  
THE NOGAPS AND JMA HAVE GONE BACK TO NOT HAVING ANY PCPN REACH OUR  
CWA UNTIL SATURDAY.  
 
SO THE ACTIVE MIDDLE STRETCH OF THE LONG TERM CONTINUES WITH  
TEMPERATURES CLOSER TO THE NORMAL. THE POTENTIAL REMAINS FOR A  
SOAKING RAIN CENTERED AROUND FRIDAY, ALTHOUGH THERE REMAINS  
UNCERTAINTIES AS TO THE IMPACT WITHIN OUR CWA. LAST NIGHT'S NAEFS  
ENSEMBLE MEAN CONTINUE TO SHOW AN ANOMALOUSLY STRONG SFC LOW  
PRESSURE SYSTEM FOR EARLY AUGUST WITH A FIVE YEAR RETURN PERIOD AND  
SD OF BETWEEN 2 AND 3 AS IT CROSSES THE CENTRAL APPALACHIANS.  
 
THE LACK OF THE RUN TO RUN CONTINUITY REMAINS. THE WAY THE MODELS  
RESOLVE CONVECTIVE SYSTEMS THAT WILL DEVELOP ACROSS THE MIDWEST  
AND UPPER MISSISSIPPI VALLEY AS THE LOWS MOVES EAST IS MAINLY  
WHY. THE MORE ROBUST "FEEDBACK" LENDS TO STRONGER AND FARTHER  
NORTH LOWS, WHILE MODELS WITH LESS MCV BULLSEYES HAVE WEAKER AND  
MORE SUPPRESSED SOLUTIONS. IT REMAINS HARD TO SEPARATE THE TRUE  
MCS(S) FROM PROLONGED FEEDBACK HANGOVERS. LIKELY THIS WILL BE THE  
CASE INTO WEDNESDAY AS THE CONVECTION THAT DAY IS THE CAUSE OF  
MOST OF THE MODELING HEARTBURN.  
 
TUESDAY NIGHT, THE MODEL TIMING HAS SLOWED IN MOVING THE COLD FRONT  
OFFSHORE AND WE MAINTAIN LOW POPS SOUTHEAST PART OF OUR CWA FOR  
THUNDERSTORMS. GIVEN HOW DRIER AIR IS MOVING, THE MORE ROBUST STORMS  
SHOULD BE DONE BY THIS TIME PERIOD. WE ARE EITHER AT OR SLIGHTLY  
ABOVE STAT GUIDANCE FOR MINS GIVEN THE SLOWER MODELING TREND.  
 
WEDNESDAY, REMAINS POPLESS AS HIGH PRESSURE BUILDS INTO THE REGION.  
THE GFS IS STANDING ALONE WITH STGR CAA AND OVERALL STRONGER SFC  
WINDS. IT ALSO STANDS ALONE WITH CHANNELIZED VORT MAX PCPN GETTING  
INTO THE NORTHERN PART OF OUR CWA. GIVEN THE DP/DT TREND, GOING  
FASTER DOES NOT SEEM TO HAVE MUCH CORROBORATION. WE ARE CLOSER TO  
A NON-GFS SOLUTION AND NAM MOS FOR HIGH TEMPS. ALSO NO POPS. BUT,  
CONVECTIVE TEMPS SHOULD BE REACHED NORTH AND SOME POPCORN TO MAYBE  
EVEN CIG CU LIKELY. WHILE IT WILL BE DRIER, NOT OUT OF THE  
QUESTION OF A COUPLE OF MORE 90S IN THE EASTERN/COASTAL PART OF  
OUR CWA.  
 
WEDNESDAY NIGHT, DRY, AS THIS IS ONE FORECAST PERIOD ALL OF THE  
MODELS AGREE UPON. WITH HIGH PRESSURE OVER THE AREA, COMFORTABLE  
STAT GUIDANCE MINS LOOK REASONABLE.  
 
THURSDAY, POPS WERE MOVED BACK APPROXIMATELY 12 HOURS. TOO LATE  
IN ITS FORECAST CYCLE TO HAVE CONFIDENCE IN THE WRF/NAM TIMING, BUT  
MANY OF THE MODELS DO NOT HAVE ANY MEASURABLE AT ALL THURSDAY DAY  
BASED ON THE MORE ROUNDABOUT APPROACH FOR THE SHORT WAVES.  
BECAUSE OF THE DRIER TRENDING, WE WENT ABOVE STAT GUIDANCE FOR MAX  
TEMPS.  
 
THURSDAY NIGHT THROUGH FRIDAY NIGHT THERE UNFORTUNATELY REMAINS  
UNCERTAINTY AS TO THE EVOLUTION OF THE SYSTEM, BUT THE SYNOPTIC SCALE  
SET-UP STILL POINTS TO HEAVY RAIN, EVEN IF IT DOES NOT NECESSARILY  
OCCUR OR AFFECT OUR CWA THE MOST. THE HEAVY RAIN WILL BE TIED TO  
CONVECTION AND THUS HOW UNSTABLE ALOFT IT BECOMES WITHIN OUR CWA  
WILL DETERMINE THE FINAL OUTCOME. HIGHEST POPS ARE THURSDAY NIGHT  
AND FRIDAY WITH THUNDER EMPHASIZED MORE FOR THE SOUTHERN PART OF OUR  
CWA. COME FRIDAY NIGHT THE PREDICTED INSTABILITY (REALLY LACK  
THEREOF) ALOFT DOES NOT SUBSTANTIATE THE ECMWF'S PCPN/QPF  
SOLUTION AND WAS NOT USED. THIS DOES NOT MEAN HEAVIER RAIN COULD NOT  
HAPPEN EARLIER. MAX TEMPS MAY VERY WELL BE OVERSTATED ON FRIDAY IF  
THIS TIMING HOLDS.  
 
BECAUSE OF TIMING DISCREPANCIES WE KEPT IN A LOW CHANCE FOR  
PRECIPITATION ON SATURDAY. AFTER ABOVE, THE END OF THE LONG TERM  
APPEARS QUIET AS HIGH PRESSURE NOSES ITS WAY SOUTHWARD FROM CANADA  
AND THE FRONTAL BOUNDARY AND LOW PRESSURE SYSTEMS MOVE OFFSHORE.  
 

 
   
AVIATION /20Z MONDAY THROUGH SATURDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD, BUT CONFIDENCE  
ISN'T AT ALL TIME HIGH DUE TO HIGH RES SOLUTIONS. THE HRRR CONTINUES  
TO DEVELOP A SOLID PRE-FRONTAL LINE OUT IN CENTRAL PA AND MOVES SAID  
LINE INTO THE REGION. SAT PIX NOR RADAR SUPPORTS THIS. SO AS OF NOW,  
THE TAFS ARE PRECIP FREE. THE EXCEPTION IS A PROB 30 FOR KPHL (30  
HOUR TAF) FOR LATE TOMORROW AS THE COLD FRONT STALLS ALONG THE COAST.  
 
WINDS WILL GUST OUT OF THE SOUTHWEST TO 20 KT FOR THE REMAINDER OF  
THE AFTERNOON.  
 
OUTLOOK...  
TUESDAY NIGHT...MOSTLY VFR CONDITIONS. ISOLATED TO PERHAPS SCATTERED  
SHWRS/TSTORMS ARE POSSIBLE VERY EARLY SOUTHEASTERN TERMINALS.  
 
WEDNESDAY AND WEDNESDAY NIGHT...MAINLY VFR CONDITIONS.  
 
THURSDAY THROUGH FRIDAY NIGHT...MVFR CONDITIONS DURING  
SHWRS/TSTORMS, WITH SOME IFR CONDITIONS POSSIBLE. WHILE CONFIDENCE  
OF OCCURRENCE IS INCREASING, TIMING CONFIDENCE REMAINS LOW.  
 
SATURDAY...PREDOMINATELY VFR CONDITIONS EXPECTED TO RETURN AS  
SHOWER FREQUENCY DIMINISHES.  
 

 
   
MARINE
 
 
WILL KEEP THE SMALL CRAFT ADVISORY HEADLINES IN PLACE TONIGHT FOR  
THE OCEAN WATERS AND EXTEND THEM THROUGH TOMORROW. GUSTS TO 25 KTS  
CAN BE EXPECTED ALONG WITH SEAS IN THE 4 TO 6 FT RANGE. WAVEWATCH  
NUMBERS WERE HIGHER AND WERE TRIMMED.  
 
IN DELAWARE BAY, WE'LL TOP THE WIND GUSTS OUT AT 20 KTS (SUB  
SMALL CRAFT).  
 
OUTLOOK...  
TUESDAY NIGHT...SMALL CRAFT ADVISORY CONDITIONS FOR SEAS ON THE  
OCEAN MIGHT LAST INTO THE EVENING. CONFIDENCE TOO LOW TO EXTEND.  
 
WEDNESDAY THROUGH THURSDAY...SUB-ADVISORY CONDITIONS ARE EXPECTED.  
 
THURSDAY NIGHT THROUGH FRIDAY NIGHT...MOSTLY SUB-SCA CONDITIONS;  
HOWEVER, A STALLED FRONT AND A WAVE OF LOW PRESSURE MOVING ALONG IT  
COULD ENHANCE SEAS AND/OR WINDS FOR THE COASTAL WATERS, MAKING SCA  
CONDITIONS POSSIBLE.  
 
SATURDAY...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED TO RETURN.  
THIS IS BASED ON TIMING OF WAVES OF LOW PRESSURE CLOSE, CONFIDENCE  
AT THIS JUNCTURE IS LESS THAN AVERAGE.  
 

 
   
RIP CURRENTS
 
 
THERE IS A MODERATE RISK FOR THE FORMATION OF DANGEROUS RIP  
CURRENTS FOR THE NEW JERSEY SHORE AND THE DELAWARE BEACHES THROUGH  
TONIGHT. THIS MODERATE RISK MIGHT EXTEND INTO TUESDAY.  
 

 
 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT TUESDAY FOR ANZ450>455.  
 

 
 

 
SYNOPSIS...GIGI/KLINE  
NEAR TERM...KRUZDLO  
SHORT TERM...KRUZDLO  
LONG TERM...GIGI  
AVIATION...GIGI/KLINE/KRUZDLO  
MARINE...GIGI/KLINE/KRUZDLO  
RIP CURRENTS...  
 
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