912  
FXUS61 KPHI 241407  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
1007 AM EDT SUN JUL 24 2016  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL REMAIN IN CONTROL OVER THE AREA UNTIL A WEAK  
WARM FRONT RETURNS BACK TO THE NORTH AND EAST BY LATE TONIGHT.  
THIS COLD FRONT IS EXPECTED TO APPROACH FROM THE NORTHWEST MONDAY  
BEFORE SLOWLY MOVING INTO THE AREA MONDAY NIGHT. THE FRONT MAY  
STALL OVER THE DELMARVA OR NEARBY TO OUR SOUTH MIDWEEK AS HIGH  
PRESSURE BUILDS IN FROM THE NORTH. ANOTHER FRONT MAY AFFECT THE  
AREA LATE THIS WEEK INTO NEXT WEEKEND.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
A WEAK COLD FRONT THAT MOVED THROUGH THE AREA LAST NIGHT WAS LOCATED  
TO OUR SOUTH ACROSS THE SOUTHERN HALF OF VA. HIGH PRESSURE CENTERED  
TO OUR NORTH WAS BUILDING INTO THE FORECAST AREA IN WAKE OF THIS  
FRONT.  
 
THE TERM COLD FRONT MAY BE SOMEWHAT MISLEADING AS THE AIR IS  
NOMINALLY COOLER BEHIND THE FRONT; CERTAINLY NOT ENOUGH TO BREAK  
THE ONGOING HEATWAVE. HIGH TEMPERATURES ACROSS MOST OF THE AREA  
WILL BE IN THE MID 90S TODAY (80S ACROSS THE HILLY TERRAIN IN  
NORTHEAST PA AND NORTHWEST NJ AS WELL AS AT THE BEACHES). HOWEVER,  
THE POST-FRONTAL AIRMASS WILL BE DRIER WITH DEWPOINTS DROPPING  
INTO THE LOW 60S AND EVEN 50S. THEREFORE, HUMIDITY WON'T BE MUCH  
OF A FACTOR TODAY ACROSS MOST OF THE AREA WITH THE HEAT INDEX  
SIMILAR TO THE DRY-BULB TEMPERATURE. THE ONE EXCEPTION WILL BE  
CENTRAL/SOUTHERN DE AND ADJACENT EASTERN MD, WHERE THE SURGE OF  
DRIER AIR WILL NOT MAKE MUCH ADVANCEMENT THAT FAR SOUTH WITH MORE  
OF AN ONSHORE COMPONENT TO THE FLOW TODAY (EITHER EASTERLY OR  
WESTERLY WINDS WILL ADVECT HIGHER DEWPOINTS INLAND THIS AFTERNOON  
WITH BAY BREEZES. FORECAST HEAT INDICES IN THESE SOUTHERN MOST  
ZONES WILL RANGE FROM 98-102F FOR THIS AFTERNOON, JUST SHY OF HEAT  
ADVISORY CRITERIA.  
 
ALTHOUGH AN OFFSHORE FLOW WILL DEVELOP LATER TODAY IN EASTERN PA AND  
WESTERN NJ, THE ONSET OF IT WILL BE DELAYED LATE ENOUGH IN THE DAY  
AND THE WINDS WILL BE LIGHT ENOUGH TO ALLOW THE SEA BREEZE TO MOVE  
INLAND THIS AFTERNOON. HI-RES MODEL GUIDANCE INDICATES THE BAY/SEA  
BREEZE FRONT REACHING THE I-95 CORRIDOR PRIOR TO SUNSET (6-8 PM).  
WINDS WILL SHIFT FROM W-SW TO S-SE ONCE THE SEA BREEZE PASSES  
THROUGH.  
 
12Z RAOBS FROM IAD, OKX AND PBZ CAPTURES A STRONG MID-LEVEL  
SUBSIDENCE INVERSION OVERHEAD. FORECAST SOUNDINGS AS WELL AS  
MODIFIED RAOB SOUNDINGS INDICATES THIS INVERSION SHOULD CAP  
CONVECTION TODAY, ESPECIALLY IN THE ABSENCE OF DEEPER ORGANIZED LIFT  
OVER THE AREA.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/
 
 
THE EVENING WILL START OFF PRECIPITATION FREE, BUT AS WE GO THROUGH  
THE NIGHT, THE FRONTAL BOUNDARY TO OUR SOUTH WILL BEGIN LIFTING  
NORTHWARD, WHILE A SHORT WAVE/VORTICITY IMPULSE APPROACHES FROM THE  
WEST. THIS SHORT WAVE IS EXPECTED TO INTERACT WITH THE LIFTING  
FRONTAL BOUNDARY AND CREATE ISOLATED/SCATTERED SHOWERS OR  
THUNDERSTORMS DURING THE OVERNIGHT HOURS. THE BEST CHANCE FOR ANY  
PRECIPITATION OVERNIGHT LOOKS TO BE THE NORTHERN TWO-THIRDS OF THE  
AREA.  
 
THERE COULD ALSO BE SOME PATCHY FOG NORTH OF THE LIFTING WARM  
FRONTAL BOUNDARY OVERNIGHT WITH A WARM AND MOISTENING AIRMASS MOVING  
NORTHWARD.  
 

 
   
LONG TERM /MONDAY THROUGH SATURDAY/
 
 
THE MAIN IMPACT WILL BE THE HEAT AND HUMIDITY FOR THE EARLY PART OF  
THE WEEK. EXPECT HIGH TEMPERATURES IN THE MID TO UPPER 90S ACROSS  
THE AREA MONDAY. THIS, COMBINED WITH A VERY HUMID AIRMASS WILL PUSH  
HEAT INDEX VALUES ABOVE 100 DEGREES FOR MOST OF THE AREA. A WEAK  
COLD FRONT WILL PUSH ACROSS THE REGION LATE MONDAY AND MONDAY NIGHT.  
THIS WILL SPARK OFF THE NEXT ROUND OF SHOWERS AND THUNDERSTORMS WITH  
THE POTENTIAL FOR SOME TO BECOME SEVERE.  
 
THIS COLD FRONT WILL SLIDE TO OUR SOUTH BY TUESDAY, BRINGING SOME  
SLIGHT MODERATION IN TEMPERATURES AND HUMIDITY LEVELS. STILL EXPECT  
TEMPERATURES IN THE LOWER TO MID 90S WITH HEAT INDEXES THAT APPROACH  
100. MUCH OF THE AREA SHOULD STAY DRY TUESDAY AND WEDNESDAY, WITH  
JUST EXTREME SOUTHERN NEW JERSEY AND THE DELMARVA WITH THE THREAT OF  
THUNDER DUE TO THE PROXIMITY TO THE STALLED FRONTAL BOUNDARY  
LINGERING ACROSS THE MID-ATLANTIC. THE SLIGHT DOWNWARD TREND OF HEAT  
AND HUMIDITY LEVELS WILL CONTINUE ON WEDNESDAY WITH TEMPERATURES  
GENERALLY STAYING IN THE LOWER 90S.  
 
THE FRONT STARTS TO APPROACH BACK FROM THE SOUTH AS A WARM FRONT BY  
WEDNESDAY NIGHT INTO THURSDAY. A COUPLE OF WEAK WAVES OF LOW  
PRESSURE MAY DEVELOP AND THEN RIDE UP ALONG THIS BOUNDARY GIVING US  
A COUPLE OF CHANCES FOR SHOWER AND THUNDERSTORM DEVELOPMENT FOR THE  
LATTER PART OF THE WEEK. THERE DOES NOT LOOK TO BE MUCH IN THE WAY  
OF A PATTERN CHANCE INTO NEXT WEEKEND, SO EXPECT THE WARM, HUMID AND  
UNSETTLED WEATHER TO CONTINUE THROUGH THE END OF THE WEEK AND NEXT  
WEEKEND.  
 

 
   
AVIATION /14Z SUNDAY THROUGH THURSDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
THERE IS SOME PATCHY LIGHT FOG THIS MORNING, MAINLY AT MIV AND OTHER  
RURAL AREAS, BUT THIS WILL LIFT AND BURN OFF AROUND/SHORTLY AFTER  
SUNRISE. THE REST OF THE DAY WILL BE VFR. IT IS POSSIBLE THAT SOME  
PATCHY FOG COULD DEVELOP AGAIN OVERNIGHT TONIGHT INTO MONDAY  
MORNING. ALSO, THERE IS A CHANCE FOR ISOLATED/SCATTERED SHOWERS OR  
THUNDERSTORMS OVERNIGHT TONIGHT.  
 
WINDS ARE LIGHT AND VARIABLE AT MANY LOCATIONS THIS MORNING, BUT  
WHERE THEY HAVE A DIRECTION, THEY ARE MORE NORTHWEST AND WILL LIKELY  
BECOME NORTH TO NORTHEAST LATER THIS MORNING. WINDS ARE EXPECTED TO  
BECOME MORE SOUTH TO SOUTHWEST DURING BY MIDDAY AS HIGH PRESSURE  
WEAKENS AS IT TRIES TO MOVE ACROSS THE AREA.  
 
OUTLOOK... VFR MUCH OF THE TIME. SCATTERED (MOSTLY) LATE  
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS MAY LIMIT  
CIGS/VSBYS AT TIMES THROUGH THE PERIOD. THE BEST CHANCE FOR THIS  
WILL BE MONDAY AFTERNOON AND EVENING AND THEN AGAIN ON THURSDAY.  
 

 
   
MARINE
 
 
SUB-SMALL CRAFT ADVISORY CONDITIONS WILL CONTINUE TODAY AND TONIGHT  
ACROSS THE AREA. THERE IS A CHANCE OF SHOWERS OR THUNDERSTORMS LATE  
TONIGHT INTO MONDAY MORNING.  
 
OUTLOOK...  
MOSTLY A PERIOD OF SUB-SCA CONDITIONS EXPECTED. SCATTERED  
SHOWERS AND THUNDERSTORMS WILL CREATE LOCALLY HIGHER WINDS AND SEAS  
THROUGH THE PERIOD. BEST CHANCE FOR THIS WILL BE MONDAY AFTERNOON  
AND EVENING AND THURSDAY.  
 

 
   
CLIMATE
 
 
YESTERDAY, JULY 23RD, WAS THE HOTTEST DAY IN QUITE SOME TIME (3 TO 4  
YEARS) AT SEVERAL OF OUR CLIMATE SITES:  
 
PHILADELPHIA: THE MAX TEMPERATURE OF 97F YESTERDAY WAS THE HIGHEST  
TEMPERATURE OBSERVED AT PHL AIRPORT IN THREE YEARS (SINCE JULY 19,  
2013 WHEN IT WAS ALSO 97F).  
 
READING: THE MAX TEMPERATURE OF 98F YESTERDAY AT RDG AIRPORT WAS  
THE HIGHEST READING IN FOUR YEARS (SINCE JULY 18, 2012 WHEN IT WAS  
100F).  
 
TRENTON: THE MAX TEMPERATURE OF 96F YESTERDAY AT TRENTON WAS THE  
HIGHEST TEMPERATURE RECORDED AT THE SITE IN THREE YEARS (SINCE JULY  
18, 2013 WHEN IT WAS ALSO 96F).  
 
THE FORECAST HIGH TEMPERATURE FOR PHILADELPHIA TOMORROW, MONDAY,  
JULY 25TH IS CURRENTLY 98F. THE LAST TIME THE TEMPERATURE REACHED OR  
EXCEEDED 98F AT PHL WAS THREE YEARS AGO ON JULY 18, 2013. THE LAST  
100-DEGREE DAY AT PHL OCCURRED FOUR YEARS AGO ON JULY 18, 2012.  
 
RECORD HIGH TEMPERATURES TODAY THROUGH THURSDAY ARE BELOW. EXCEPT  
MAYBE ABE, WE'LL FALL SHORT OF RECORD HIGHS TODAY. WE MAY TIE OR  
BREAK DAILY RECORD HIGHS TOMORROW AT SEVERAL OF OUR CLIMATE  
SITES.  
 
SITE 24TH 25TH 26TH 27TH 28TH  
---- ---- ---- ---- ---- ----  
 
PHL... 98-2011 96-1899 101-1892 101-1940 100-1941  
 
ABE... 95-1999 95-1999 98-1940 98-1955 97-1949  
 
ACY... 100-2011 99-2010 96-2011 99-2005 98-1999  
 
ILG... 98-2011 96-1987 99-1894 100-1894 101-1894  
 
TTN... 98-1910 97-1999 99-1892 100-1894 101-1894  
 
GED... 99-2011 99-2010 97-2012 98-2005 99-1949  
 
RDG... 96-2010 96-1999 99-1940 98-1955 99-1941  
 
MPO... 91-1914 90-1999 89-1949 91-1955 93-1949  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...HEAT ADVISORY FROM 11 AM TO 6 PM EDT MONDAY FOR PAZ060>062-101-  
103-105.  
EXCESSIVE HEAT WARNING UNTIL 6 PM EDT MONDAY FOR PAZ070-071-  
102-104-106.  
NJ...HEAT ADVISORY FROM 11 AM TO 6 PM EDT MONDAY FOR NJZ001-007>010-  
012>014-016-020>027.  
EXCESSIVE HEAT WARNING UNTIL 6 PM EDT MONDAY FOR NJZ015-  
017>019.  
DE...HEAT ADVISORY FROM 11 AM TO 6 PM EDT MONDAY FOR DEZ002>004.  
EXCESSIVE HEAT WARNING UNTIL 6 PM EDT MONDAY FOR DEZ001.  
MD...HEAT ADVISORY FROM 11 AM TO 6 PM EDT MONDAY FOR MDZ008-012-015-  
019-020.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...KLEIN/JK  
NEAR TERM...KLEIN  
SHORT TERM...ROBERTSON  
LONG TERM...JK  
AVIATION...ROBERTSON  
MARINE...ROBERTSON/JK  
CLIMATE...KLEIN  
 
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