492  
FXUS61 KPHI 021031  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
631 AM EDT TUE SEP 2 2014  
   
SYNOPSIS
 
 
A FRONTAL BOUNDARY WILL MOVE THROUGH THE REGION TONIGHT, THEN  
THIS FRONT WILL BE LOCATED SOUTH OF OUR REGION WEDNESDAY AS HIGH  
PRESSURE BUILDS OVERHEAD. HIGH PRESSURE WILL GRADUALLY MOVE FROM  
WEST TO EAST ACROSS THE EASTERN UNITED STATES THROUGH THE SECOND  
HALF OF THE WEEK. ON SATURDAY, A COLD FRONT WILL MOVE THROUGH THE  
REGION. THIS FRONT WILL STALL TO OUR SOUTHEAST FOR THE EARLY PART  
OF NEXT WEEK WITH HIGH PRESSURE OVER THE GREAT LAKES.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
WHILE THE CALENDAR SAYS SEPTEMBER, IT WILL CONTINUE TO FEEL LIKE  
THE HEART OF SUMMER AS THE HEAT AND HUMIDITY REMAINS ACROSS THE  
AREA. THERE COULD BE SOME SLIGHT RELIEF THROUGH THE DAY AS THE  
SURFACE DEW POINTS ARE FORECAST TO LOWER SOME. SYNOPTICALLY, HIGH  
PRESSURE CONTINUES TO BE CENTERED IN THE WESTERN ATLANTIC HELPING TO  
PUMP UP THE HEAT AND HUMIDITY WITHIN A SOUTHWESTERLY FLOW. THERE IS  
HOWEVER A NOTABLE UPPER-LEVEL TROUGH THAT WILL BE SWINGING ACROSS  
THE GREAT LAKES REGION AND THE UPPER OHIO VALLEY THROUGH THE DAY.  
THERE IS A SURFACE FRONT WITH THIS FEATURE, HOWEVER IT WILL REMAIN  
WELL TO OUR WEST DURING THE DAY. THERE SHOULD BE A PRE-FRONTAL  
TROUGH DEVELOPING GIVEN THE WARM TO HOT AIRMASS. THE EVENTUAL  
SURFACE FRONT MAY JUMP INTO THIS TROUGH AS WE WORK OUR WAY INTO THE  
SHORT TERM /TONIGHT/. THE FORECAST CHALLENGES FOR TODAY REVOLVES  
AROUND THE CONVECTIVE CHCS AND ALSO THE HEAT INDICES.  
 
AS THE UPPER-LEVEL TROUGH PROGRESSES EASTWARD, THE MAIN SHORT  
WAVE IS FORECAST TO LIFT TO OUR NORTH LATE THIS AFTERNOON. THIS  
LEAVES BEHIND THE TAIL END OF IT SLIDING INTO OUR AREA. AS A  
RESULT, THE LARGE SCALE FORCING SHOULD SLIDE TO OUR NORTHWEST  
LATER THIS AFTERNOON. THERE WILL HOWEVER BE INSTABILITY IN PLACE  
ALTHOUGH THIS CAN BE AFFECTED BY THE LOWERING DEW POINTS /AT LEAST  
SBCAPE/. THERE IS SOME INCREASE IN THE MID LEVEL FLOW, HOWEVER THE  
CORE /50-60 KNOTS/ OF IT IS FORECAST TO REMAIN WELL TO OUR WEST  
WHICH IS WHERE THE SLIGHT RISK FOR SEVERE THUNDERSTORMS IS  
INDICATED. THAT STRONGER FLOW IS EXPECTED TO ALLOW FOR CONVECTIVE  
DEVELOPMENT WELL TO OUR WEST AND THIS IS WHAT WE WILL PROBABLY  
HAVE TO WAIT AND SEE WHAT SURVIVES AS IT TRACKS EASTWARD. IN  
ADDITION, SOME ISOLATED ACTIVITY COULD FIRE ALONG THE PRE-FRONTAL  
TROUGH. AS A RESULT, WE SLOWED DOWN THE POP INCREASE FROM WEST TO  
EAST. WHILE AN ISOLATED CELL COULD FORM THIS AFTERNOON FARTHER  
EAST FROM LOCAL CONVERGENCE, MUCH OF THE TIME WILL PROBABLY BE  
RAIN-FREE.  
 
REGARDING THE HEAT, THE 850 MB TEMPERATURES ARE FORECAST TO BE A FEW  
DEGREES WARMER THAN YESTERDAY. THE FORECAST SOUNDINGS INDICATE THE  
POTENTIAL FOR BETTER MIXING BEING PRESENT AS THE PRESSURE GRADIENT  
TIGHTENS SOME AND THE LOW-LEVEL LAPSE RATES STEEPEN. THEREFORE THIS  
SHOULD RESULT IN HIGH TEMPERATURES INTO THE LOWER TO EVEN MID 90S  
FOR MANY INLAND AREAS. THE MIXING HOWEVER SHOULD LOWER THE SURFACE  
DEW POINTS SOME IN THE AFTERNOON, KEEPING THE HEAT INDICES A BIT  
LOWER. AS A RESULT, WE ARE EXPECTING THE HEAT INDICES TO REMAIN  
UNDER ADVISORY CRITERIA INCLUDING THE PHILADELPHIA METRO AREA.  
 
HIGH TEMPERATURES WERE A BLEND OF THE NAM/GFS MOS, ALTHOUGH THE  
WARMER NAM MOS WAS FAVORED FOR SOME AREAS WHICH ALSO GOT US CLOSE TO  
CONTINUITY. THE HOURLY GRIDS WERE TWEAKED USING THE LAMP/LAV  
GUIDANCE, ESPECIALLY THIS MORNING TO HELP ASSIST WITH  
TEMPERATURE/DEW POINT TRENDS THUS FAR.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/
 
 
THE AFOREMENTIONED UPPER-LEVEL TROUGH WILL GENERALLY GLANCE OUR  
AREA, WITH A FRONTAL BOUNDARY SWEEPING THROUGH. THE MAIN FORCING AND  
ASSOCIATED MID LEVEL JET MAX IS FORECAST TO BYPASS OUR AREA TO THE  
NORTHWEST. THERE STILL IS SOME INCREASE IN THE FLOW WITH THIS SYSTEM  
AS THE TAIL END OF THE SHORT WAVE MOVES THROUGH. THIS IN CONJUNCTION  
WITH ENOUGH INSTABILITY SHOULD SUPPORT SOME CONVECTION THIS EVENING  
BEFORE WEAKENING TAKES PLACE. THE AMOUNT OF SHEAR LOOKS LOW AND  
THEREFORE STORM ORGANIZATION SHOULD BE WEAK AND POTENTIALLY EVEN  
DISAPPEAR AS THE EVENING WEARS ON.  
 
THE FORECAST SOUNDINGS INDICATE SOME OPPORTUNITY FOR SOME STRONGER  
CORES ACROSS OUR WESTERN ZONES AND TOWARDS THE DELMARVA, HOWEVER  
GIVEN THE BEST FORCING AND SHEAR MISSING OUR AREA THE SEVERE WEATHER  
THREAT LOOKS RATHER LOW AS OF NOW. THEREFORE, NO ENHANCED WORDING  
WAS CARRIED ATTM. WE USED CHC POPS THIS EVENING THEN THESE LOWER  
FROM WEST TO EAST. ANY LINGERING CONVECTION SHOULD BE DONE AFTER  
MIDNIGHT AS THE FRONTAL BOUNDARY SHIFTS EASTWARD. THE MODEL GUIDANCE  
SHOWS A PLUME OF PW AROUND 2 INCHES SURGING AHEAD OF THE SURFACE  
FRONT, THEREFORE ANY CONVECTION WILL HAVE THE POTENTIAL TO PRODUCE  
BRIEF TORRENTIAL DOWNPOURS. ANY FLOOD THREAT SHOULD BE LIMITED  
HOWEVER.  
 
THERE IS NO SIGNIFICANT AIRMASS CHANGE BEHIND THE SURFACE FRONT  
DESPITE A WIND SHIFT TO THE NORTHWEST. AS THE CLOUDS THIN OUT SOME  
SURFACE COOLING WILL TAKE PLACE, HOWEVER THE DEW POINTS LOOK TO  
REMAIN ON THE MUGGY SIDE FOR MUCH OF THE NIGHT. SOME LOWERING SHOULD  
START TO TAKE PLACE THOUGH LATE MAINLY OVER OUR WESTERN ZONES. THE  
COMBINATION OF LIGHT WINDS AND LINGERING LOW-LEVEL MOISTURE, MAY  
ALLOW FOR SOME FOG TO DEVELOP PARTICULARLY WHERE DRY AIR ADVECTION  
IS DELAYED. WE ARE NOT EXPECTING A LOT OF FOG, AND GIVEN LOWER  
CONFIDENCE WE HELD OFF INCLUDING A MENTION ATTM.  
 
AS FOR LOW TEMPERATURES, AN EVEN BLEND OF THE GFS/NAM WAS MAINLY  
USED.  
 

 
   
LONG TERM /WEDNESDAY THROUGH MONDAY/
 
 
WEDNESDAY THROUGH FRIDAY: DRY WITH FEW CLOUDS, FLOW TURNING  
GRADUALLY TO THE SOUTHWEST BY FRIDAY. THINK THE 00Z GFS IS TO QUICK  
SHOWING SOME RETURN FLOW POPS. MUGGY AND HOT AS WELL BUT TEMPS WILL  
BE UNDER HEAT ADVISORY CRITERIA. FAIR SHOT AT 90 THU/FRI FOR PHL.  
WENT AT OR A TOUCH ABOVE MET/MAV GUIDANCE ON TEMPERATURES BASED ON  
THE 925/850 MB TEMPERATURE PROFILES.  
 
FRIDAY NIGHT THROUGH SATURDAY NIGHT: A FRONTAL BOUNDARY MOVING SOUTH  
FROM THE GREAT LAKES WILL BE A TRIGGER FOR SOME SCATTERED SHOWERS  
AND THUNDERSTORMS. CLOUDS SHOULD INCREASE FROM NORTHWEST TO  
SOUTHEAST FRIDAY NIGHT AND SATURDAY. CONTINUED SOUTHWEST FLOW WILL  
BE IN PLACE AS WELL AHEAD OF THE FRONT. 925 MB TEMPS ARE LIKELY TO  
BE A TOUCH HIGHER THAN THU/FRI INDICATING SLIGHTLY WARMER SURFACE  
TEMPERATURES. TEMPERATURES COULD POSSIBLY MAKING A RUN AT THE LOW  
PERHAPS MID 90'S BASED ON HOW QUICKLY THE CLOUDS INCREASE. WENT  
WARMER THAN WPC/MEX GUIDANCE IN THESE PERIODS TO ACCOUNT FOR THE  
WAA AHEAD OF THE FRONT. IN TERMS OF ANY STRONG TO SEVERE STORMS. A  
MODEST AMOUNT OF INSTABILITY (CAPE AROUND 1500 J/KG) WILL BE  
PRESENT WITH MODERATELY STEEP LAPSE RATES. HOWEVER THE LACK OF  
SHEAR IN PLACE WILL LIKELY PREVENT ANY WIDESPREAD COVERAGE OF  
STRONG TO SEVERE STORMS. CONTINUED THUNDER IN GRIDS FOR SAT-SAT  
NIGHT WITH CHANCE POPS.  
 
SUNDAY THROUGH TUESDAY: NORTHEAST FLOW WILL DEVELOP EARLY NEXT WEEK  
WITH THE FRONT TO OUR SOUTH AND HIGH PRESSURE OVER THE GREAT LAKES.  
THE 00Z GFS IS THE MOST AGGRESSIVE CLEARING THE FRONT DURING THE DAY  
SUNDAY WITH ONLY LINGERING SHOWERS ACROSS THE SOUTH. THE 00Z ECMWF  
AND CMC SLOW THE FRONT ALLOWING FOR ADDITIONAL SHOWER CHANCES FOCUSED  
ACROSS THE SOUTH, PARTICULARLY ON SUNDAY BUT LINGER ISOLATED SHOWERS  
INTO MONDAY AND TUESDAY. THE ECMWF APPEARS TO BE FASTER THAN IT'S  
PREVIOUS RUN AND SOME MEMBERS WITHIN THE 18Z GFS ENSEMBLE SUITE  
ARGUE FOR A SLOWER FRONTAL PASSAGE. A MIDDLE GROUND WILL BE USED  
WITH CHANCE POPS DECREASING FROM NORTH TO SOUTH SUNDAY WITH SLIGHT  
CHANCE POPS ACROSS THE SOUTH MONDAY. CLOUDS AND SHOWERS MAY KEEP  
HIGHS DOWN ON SUNDAY AND LOWS HIGHER AT NIGHT. ON MONDAY AND TUESDAY  
AMPLE SUNSHINE MAY ALLOW MOST AREAS TO GET A TOUCH WARMER THAN WHAT  
MODELED TWO METER TEMPERATURES OR WPC GUIDANCE SUGGEST. RADIATIONAL  
COOLING MONDAY NIGHT IS LIKELY AS WELL ACROSS MOST OF THE REGION  
WITH THE FAVORED REGION JUST INLAND OFF THE NJ COAST AND NW PHL  
COULD HAVE A RELATIVITY CHILLY NIGHT.  
 

 
   
AVIATION /12Z TUESDAY THROUGH SATURDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
TODAY...SOME MVFR/IFR VISIBILITIES DUE TO FOG EARLY MAINLY AT  
KABE AND KTTN, OTHERWISE VFR. A FEW SHOWERS AND THUNDERSTORMS  
SHOULD DEVELOP LATER THIS AFTERNOON MAINLY WEST OF KPHL AND  
THEREFORE A TEMPO GROUP WILL BE ADDED TO KRDG AND KABE. A VCSH WAS  
CARRIED ELSEWHERE LATE. LIGHT TO EVEN CALM WINDS, BECOMING  
SOUTHWEST AND INCREASING TO 10-15 KNOTS TOWARD MIDDAY. SOME LOCAL  
GUSTS UP TO 20 KNOTS SHOULD OCCUR THIS AFTERNOON AS ENOUGH MIXING  
DEVELOPS.  
 
TONIGHT...A FRONTAL BOUNDARY WILL MOVE THROUGH WITH SOME SHOWERS AND  
THUNDERSTORMS ARRIVING FROM THE WEST, WHICH MAY TEND TO DIMINISH  
WITH AN EASTWARD EXTENT. A WIND SHIFT TO THE NORTHWEST IS ANTICIPATED  
WITH ANY CONVECTION AND ALSO AS THE FRONT MOVES THROUGH. MVFR  
CEILINGS WITH VISIBILITIES AS LOW AS IFR WILL BE POSSIBLE WITH ANY  
SHOWER OR THUNDERSTORM, OTHERWISE VFR. THERE IS A CHANCE SOME LOCAL  
FOG DEVELOPS LATE AS CLOUDS THIN AND THE WINDS DROP OFF WITH THE  
LOW-LEVEL MOISTURE REMAINING.  
 
OUTLOOK...  
WEDNESDAY THROUGH FRIDAY NIGHT: VFR.  
 
SATURDAY: MVFR TO IFR RESTRICTIONS POSSIBLE IN ANY AFTERNOON OR  
EVENING THUNDERSTORMS.  
 

 
   
MARINE
 
 
A SOUTHERLY FLOW WILL BE MAINTAINED TODAY WELL AHEAD OF A SURFACE  
FRONT. THERE WILL BE SOME INCREASE LATER THIS AFTERNOON AND EVENING  
AS THE PRESSURE GRADIENT TIGHTENS SOME, HOWEVER THESE ARE EXPECTED  
TO REMAIN BELOW ADVISORY CRITERIA. THE WINDS WILL SHIFT TO THE WEST  
AND NORTHWEST LATER TONIGHT BEHIND THE FRONTAL PASSAGE. SOME  
THUNDERSTORMS ARE POSSIBLE WITH THE FRONT MAINLY THIS EVENING,  
HOWEVER THESE COULD WEAKEN BEFORE REACHING OUR MARINE AREA. SEAS  
WILL BE IN THE 2 TO 4 FEET RANGE OVER THE COASTAL WATERS, AND 2 FEET  
OR LESS ON DELAWARE BAY.  
 
OUTLOOK...  
WEDNESDAY THROUGH FRIDAY NIGHT: SUB SCA SEAS AND WINDS EXPECTED  
ATTM.  
 
SATURDAY: SOME STRONG WIND GUSTS POSSIBLE FROM THUNDERSTORMS,  
OTHERWISE SUB SCA SEAS AND WINDS.  
 

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

 
 

 
SYNOPSIS...GAINES/GORSE  
NEAR TERM...GORSE  
SHORT TERM...GORSE  
LONG TERM...GAINES  
AVIATION...GAINES/GORSE  
MARINE...GAINES/GORSE  
 
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