283  
FXUS61 KPHI 280138  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
938 PM EDT THU AUG 27 2015  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL SETTLE ACROSS OUR REGION OVERNIGHT AND FRIDAY,  
THEN MOVE OFFSHORE DURING THE WEEKEND. A WEAKENING COOL FRONT IS  
FORECAST TO ARRIVE LATE SUNDAY INTO MONDAY, THEN HIGH PRESSURE  
BUILDS IN FOR MONDAY INTO TUESDAY. A WEAK SYSTEM MAY SLIDE ACROSS  
OUR AREA TUESDAY, AS HIGH PRESSURE CONTINUES TO BUILD NEARBY INTO  
THURSDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
 
 
HIGH PRESSURE WAS CENTERED OVER LAKE ERIE AND VICINITY THIS  
EVENING. THE HIGH WILL DRIFT EASTWARD OVERNIGHT.  
 
THE LAST OF THE STRATOCUMULUS WILL CONTINUE TO DISSIPATE WITH A  
MAINLY CLEAR SKY ANTICIPATED. A LIGHT NORTHWEST TO NORTH SURFACE  
FLOW IS EXPECTED. TEMPERATURES SHOULD DROP INTO THE 5OS AND LOWER  
60S.  
 

 
   
SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/
 
 
THE HIGH PRESSURE SYSTEM WILL EASE ACROSS OUR CWA. THE TRANSITION  
TO WARMER AND MORE HUMID WEATHER SLOWLY STARTS ON FRIDAY. STILL  
ANOTHER SPECTACULAR LATE AUGUST DAY. THE PREDICTED CONVECTIVE  
TEMPERATURES ARE NOT SUPPOSE TO BE REACHED TIL THE AFTERNOON AND  
WITH LESS OF AN ANTECEDENT MOISTURE POOL BETWEEN 925MB AND 850MB  
FORECASTING LESS CU THAN TODAY. THE 250MB JET WILL BE FARTHER TO  
THE SOUTHEAST, SO NO JET STREAM CIRRUS PROBLEMS. AIR MASS  
MODIFICATION BY LATE IN THE AFTERNOON SUGGESTS A 1-3F BUMP IN MAX  
TEMPS FROM TODAY. THIS IS MUCH CLOSER TO NAM MOS THAN THE COOLER  
GFS MOS WHERE THE STAT GUIDANCE PARTS WAYS ON FRIDAY.  
 
OVERALL LIGHT WIND PATTERN WITH THE SEA AND BAY BREEZE MAKING  
MORE OF AN INLAND ADVANCE THAN THE PAST TWO DAYS LATE IN THE  
AFTERNOON.  
 

 
   
LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/
 
 
THE SYNOPTIC SETUP IS COMPRISED OF A RIDGE EAST OF THE CAROLINAS  
WITH AN INITIAL ZONAL FLOW ACROSS THE NORTHEAST AND MID ATLANTIC  
REGIONS. A SHORT WAVE TROUGH IS FORECAST TO BE TRAVERSING THE  
MIDWEST AND GREAT LAKES REGIONS SATURDAY AND SUNDAY, HOWEVER THIS  
FEATURE MAY END UP WEAKENING AS IT GETS TO THE NORTHEAST WITH THE  
WESTERN ATLANTIC RIDGE BUILDING WEST AND NORTH SOME. THE LEFTOVERS  
OF THE SHORT WAVE TROUGH SLIDES ACROSS OUR AREA TUESDAY AND  
WEDNESDAY, THEN AN UPPER-LEVEL RIDGE EXPANDS ACROSS THE OHIO  
VALLEY AND GREAT LAKES REGION EASTWARD THROUGH THURSDAY. WE USED A  
MODEL BLEND FOR FRIDAY NIGHT INTO SUNDAY, THEN THE 12Z WPC  
GUIDANCE THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE FOLLOWING  
ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES.  
 
FOR FRIDAY NIGHT...A RIDGE CENTERED TO OUR SOUTHEAST WILL ALLOW  
SURFACE HIGH PRESSURE TO BE OVER OUR AREA. THIS WILL BE ASSISTED  
BY A SHORT WAVE TROUGH MOVING ACROSS THE MIDWEST AND UPPER GREAT  
LAKES, ALTHOUGH THERE IS SOME VARIATIONS WITHIN THE MODEL GUIDANCE  
ON THE AMPLITUDE OF THIS FEATURE. OVERALL, CONTINUED QUIET WEATHER  
FOR OUR AREA DURING THIS TIME IS ANTICIPATED.  
 
FOR SATURDAY AND SUNDAY...A SHORT WAVE TROUGH IS FORECAST TO BE  
SLIDING ACROSS THE GREAT LAKES REGION DURING THIS TIME, HOWEVER IT  
MAY END UP WEAKENING AS IT APPROACHES THE NORTHEAST. SOME MODEL  
GUIDANCE MAINTAINS THIS FEATURE AS IT APPROACHES SUNDAY NIGHT AND  
ESPECIALLY BEYOND, HOWEVER WITH THE WESTERN ATLANTIC RIDGE TENDING  
TO BUILD SOME AND EVEN EXPAND A BIT WESTWARD, THIS FEATURE SHOULD  
NOT HAVE MUCH IN THE WAY OF AN IMPACT ON OUR WEATHER ESPECIALLY  
SINCE IT LOOKS TO APPROACH SLOWLY. THE POSSIBLE FLY IN THE  
OINTMENT MAY BE LATE SUNDAY AS COME CONVECTION UPSTREAM WITHIN THE  
LINGERING UPPER-LEVEL WEAKNESS COULD SPILL INTO OUR NORTHWEST  
ZONES. A SOUTHERLY FLOW OF WARMER AIR IS EXPECTED TO OCCUR EACH  
DAY WITH AT LEAST SOME INCREASE IN THE DEW POINTS AS WELL. THE  
LATTER SHOULD BE MORE NOTICEABLE DURING SUNDAY AS THE SOUTHERN  
FLOW IS MORE ESTABLISHED THEN, ALTHOUGH THE MOISTURE RETURN DOES  
NOT APPEAR TO BE SUBSTANTIAL.  
 
FOR MONDAY AND TUESDAY...AS A TROUGH MIGRATES ACROSS THE PACIFIC  
NORTHWEST, DOWNSTREAM RIDGING IS EXPECTED TO OCCUR. THE MODEL  
GUIDANCE SHOWS A HIGHER AMPLITUDE RIDGE OCCURRING DURING THIS TIME  
FRAME WITH THE AXIS MAINLY TO OUR WEST. SOME MODEL GUIDANCE HAS  
BEEN SHOWING THE WEAKENING SHORT WAVE TROUGH MIGRATING OVERHEAD  
DURING THIS TIME. THERE STILL COULD BE SOME CONVECTION THAT  
DEVELOPS WITH DAYTIME HEATING WITHIN A MOISTENING AIR MASS,  
HOWEVER THERE DOES NOT APPEAR TO BE ANY PRONOUNCED LARGE SCALE  
FORCING MECHANISM. THEREFORE, WE WENT WITH A DRY FORECAST.  
OTHERWISE, VERY WARM TO HOT AND HUMID FOR MUCH OF THE AREA. THE  
FLOW LOOKS LIGHT ENOUGH TO ALLOW FOR AFTERNOON SEA BREEZE  
DEVELOPMENT.  
 
FOR WEDNESDAY AND THURSDAY...A SIMILAR SYNOPTIC SETUP DURING THIS  
TIME FRAME AS WELL WITH RIDGING GENERALLY HOLDING. THIS KEEPS HIGH  
PRESSURE AT THE SURFACE CLOSE BY, WITH A BLOCKING TYPE PATTERN IN  
PLACE. TROPICAL CYCLONE ERIKA MAY BE LURKING OFF THE SOUTHEASTERN  
U.S. COAST, HOWEVER THERE IS A LOT OF UNCERTAINTY. THERE ARE SOME  
HINTS IN THE GUIDANCE THAT A TROUGH SLIDES ACROSS THE NORTHEAST  
THURSDAY BEFORE THE RIDGE BUILDS AGAIN, HOWEVER IT LOOKS WEAK AND  
BYPASSES THE TROPICAL SYSTEM. SOME GUIDANCE BRINGS THE TROPICAL  
SYSTEM FARTHER NORTH, HOWEVER THAT WOULD BE INTO THE RIDGE  
OVERALL. THE TROUGH OUT WEST WILL ASSIST IN THE DOWNSTREAM RIDGE  
PLACEMENT AND STRENGTH, THEREFORE MORE UNCERTAINTY WITH THE FLOW  
ACROSS THE EAST. FOR THE LATEST FORECAST INFORMATION ON TROPICAL  
CYCLONE ERIKA, VISIT THE NATIONAL HURRICANE CENTERS WEB SITE.  
OTHER THAN A RATHER LOW CHC FOR DIURNALLY DRIVEN CONVECTION, NO  
REAL ORGANIZED TRIGGERS APPEAR TO BE PRESENT ATTM FOR RAIN CHCS  
WHICH THE AREA NEEDS. THE VERY WARM AND HUMID CONDITIONS SHOULD  
PERSIST FOR MUCH OF THE AREA, WITH PERHAPS SOME RELAXATION IF THE  
AFOREMENTIONED TROUGH IS ABLE TO KNOCK THE HEIGHTS/TEMPERATURES  
DOWN SOME FOR A TIME.  
 

 
   
AVIATION /02Z FRIDAY THROUGH TUESDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD WITH A MAINLY  
CLEAR SKY.  
 
A LIGHT NORTHWEST TO NORTH WIND OVERNIGHT INTO FRIDAY MORNING  
SHOULD BACK TOWARD THE WEST AND SOUTHWEST ON FRIDAY AFTERNOON. THE  
SEA BREEZE FRONT MAY REACH KACY ON FRIDAY AFTERNOON.  
 
OUTLOOK...  
FRIDAY NIGHT AND SATURDAY...VFR. LIGHT SOUTHWESTERLY WINDS AT  
NIGHT, INCREASING UP TO 10 KNOTS DURING THE DAY SATURDAY.  
 
SUNDAY...A CHANCE OF LOCAL FOG EARLY, OTHERWISE VFR. A FEW  
SHOWERS AND THUNDERSTORMS MAY DEVELOP IN THE AFTERNOON AND EVENING  
WELL TO OUR WEST AND NORTHWEST.  
 
MONDAY AND TUESDAY...A CHANCE OF LOCAL FOG EACH MORNING,  
OTHERWISE MAINLY VFR. THERE COULD BE A SHOWER OR THUNDERSTORM  
AROUND ESPECIALLY TUESDAY AFTERNOON.  
 

 
   
MARINE
 
 
NO MARINE HAZARDS EXPECTED TONIGHT AND FRIDAY.  
 
OVERNIGHT, THE GENERALLY NORTHERLY GRADIENT WIND AROUND THE  
SURFACE HIGH IS PREDICTED TO RETURN.  
 
ON FRIDAY, WITH THE SURFACE HIGH PASSING ACROSS THE MARINE  
WATERS, WIND SPEEDS WILL BECOME LIGHTER WITH MORE VARIABILITY IN  
DIRECTION AS THE MORNING AND EARLY AFTERNOON PROGRESS. THEN A  
LIGHT EAST TO SOUTHEAST CIRCULATION AROUND THE SURFACE HIGH SHOULD  
DEVELOP. THIS WILL LIKELY ALSO START WORKING ITS WAY INTO DELAWARE  
BAY LATE.  
 
OUTLOOK...  
FRIDAY NIGHT THROUGH TUESDAY, HIGH PRESSURE GENERALLY DOMINATES  
THE WEATHER WITH LIGHTER FLOW. A SOUTHERLY FLOW HOWEVER SHOULD  
INCREASE SOME AT TIMES, ESPECIALLY DURING THE AFTERNOON AND  
EVENING HOURS PARTICULARLY NEARSHORE WITH THE DEVELOPMENT OF  
SEA/BAY BREEZES. OVERALL, THE CONDITIONS ARE ANTICIPATED TO REMAIN  
BELOW SMALL CRAFT ADVISORY CRITERIA.  
 

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

 
 

 
 
SYNOPSIS...GORSE  
NEAR TERM...IOVINO  
SHORT TERM...GIGI  
LONG TERM...GORSE  
AVIATION...GORSE/IOVINO  
MARINE...GIGI/GORSE  
 
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