476  
FXUS61 KPHI 230226  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
1026 PM EDT TUE AUG 22 2017  
   
SYNOPSIS
 
 
A COLD FRONT WILL MOVE INTO OUR REGION LATE TONIGHT AND SLOWLY  
EXIT OFF THE DELMARVA COAST WEDNESDAY AFTERNOON. CANADIAN HIGH  
PRESSURE BUILDS INTO THE REGION ON THURSDAY AND SHOULD CONTINUE  
TO BE THE PRIMARY INFLUENCE ON OUR WEATHER INTO EARLY NEXT WEEK.  
TWO LOW PRESSURE SYSTEMS SHOULD BE NEAR THE GULF COAST STATES  
THIS WEEKEND AND EVENTUALLY TURN NORTHEAST EARLY NEXT WEEK,  
POSSIBLY AFFECTING OUR WEATHER AROUND TUESDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
 
 
SEVERE THUNDERSTORM WATCH 464 IS IN EFFECT UNTIL MIDNIGHT FOR  
ALL OUR EASTERN PENNSYLVANIA COUNTIES EXCEPT DELAWARE AND  
PHILADELPHIA, AS WELL AS THE NEW JERSEY COUNTIES OF SUSSEX,  
WARREN, MORRIS AND HUNTERDON. IT HAS BEEN EXPANDED INTO CENTRAL  
AND SOUTHWESTERN NEW JERSEY AND THE FAR UPPER DELMARVA.  
 
SHOWERS AND THUNDERSTORMS WERE IN NORTHEASTERN MARYLAND,  
EASTERN PENNSYLVANIA AND NORTHERN NEW JERSEY AROUND 10:15 PM.  
THE CONVECTION WILL CONTINUE TO PROGRESS EASTWARD. WIND DAMAGE,  
HAIL AND HEAVY RAIN HAVE OCCURRED IN PARTS OF EASTERN  
PENNSYLVANIA AND NORTHWESTERN NEW JERSEY.  
 
THE CONVECTION IS FORECAST TO WEAKEN OVERNIGHT AS CONDITIONS  
STABILIZE. THE SKY IS EXPECTED TO REMAIN MOSTLY CLOUDY WITH  
PERHAPS SOME PATCHY FOG WHERE ANY HEAVY RAIN FALLS.  
 
LOW TEMPERATURES ARE ANTICIPATED TO BE IN THE MIDDLE AND UPPER  
60S IN THE POCONOS AND FAR NORTHERN NEW JERSEY AND IN THE LOWER  
AND MIDDLE 70S ELSEWHERE IN OUR FORECAST AREA.  
 
THE WIND SHOULD FAVOR THE SOUTHWEST AND WEST OVERNIGHT BECOMING  
NORTHWEST AROUND DAYBREAK WITH THE ARRIVAL OF A COLD FRONT.  
 

 
   
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/
 
 
ANY ONGOING SHOWERS AND THUNDERSTORMS NEAR THE COAST WILL  
SLOWLY MOVE EASTWARD TOWARDS THE WATERS THROUGH THE AFTERNOON AS  
THE COLD FRONT CONTINUES ITS SURGE EASTWARD. HUMIDITY SHOULD  
FALL TO MORE COMFORTABLE LEVELS LATER IN THE DAY, MORE SO BY  
EVENING AS A SECONDARY FRONT PUSHES THROUGH THE REGION.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/
 
 
500 MB: A -2SD TROUGH BEGINS THE LONG TERM PERIOD IN THE GREAT  
LAKES REGION, THEN WEAKENS SLIGHTLY AS IT MOVES INTO THE  
NORTHEAST FRIDAY- MONDAY. THEREAFTER, WE WILL MONITOR THE  
NORTHEASTWARD PROGRESS OF WHAT SHOULD BE A SPLIT FLOW LOW OF  
TROPICAL ORIGINS, HAVING MOVED ASHORE ALONG THE GULF COAST BY  
EARLY NEXT WEEK.  
 
TEMPERATURES: CALENDAR DAY AVERAGES THURSDAY...NEAR OR SLIGHTLY  
BELOW NORMAL, THEN 2 TO 6 DEGREES BELOW NORMAL DAILY FRIDAY-  
TUESDAY.  
 
FORECAST BASIS: A 50 50 BLEND OF 12Z/22 GFS/NAM MOS WAS USED  
WEDNESDAY NIGHT-THURSDAY NIGHT, THEN THE 12Z/22 GFS MEXMOS WAS  
APPLIED FRIDAY AND THEREAFTER THE 15Z/22 WPC D4-8 GRIDDED  
ELEMENTS OF MAX/MIN T, 12 HR POP 6 HRLY DEW/WIND/SKY.  
 
WEDNESDAY NIGHT...FAIR AND MORE SEASONABLE WITH LIGHT WIND AND  
POSSIBLE PATCHY COUNTRYSIDE FOG.  
 
THURSDAY...SCATTERED LIGHT SHOWERS POSSIBLE LATE THURSDAY IN E  
PA WITH CONSIDERABLE AFTERNOON CLOUDINESS.  
 
FRIDAY-MONDAY...HIGH PRESSURE SHIFTS SOUTHEASTWARD INTO THE  
GREAT LAKES THURSDAY THROUGH SATURDAY,THEN EASTWARD INTO  
SOUTHEASTERN CANADA/NORTHEAST U.S. SUNDAY AND MONDAY. THIS  
EXPANSIVE HIGH WILL CONTROL OUR REGIONAL WEATHER PATTERN ACROSS  
THE MID ATLANTIC DURING THIS TIME. THE TROUGH ALOFT COULD RESULT  
IN A SHOWER NORTH OF I-78 FRIDAY AFTERNOON AND THERE SHOULD BE  
CONSIDERABLE CLOUDINESS AT THAT TIME. OTHERWISE, FOR NOW, GOOD  
WEATHER IS PREDICTED.  
 
TUESDAY...WAA OVERRUNNING CLOUDS, IF NOT RAIN, FROM A POTENTIAL  
TROPICAL REMNANT MOVING NORTHEASTWARD FROM THE GULF COAST.  
 

 
   
AVIATION /03Z WEDNESDAY THROUGH SUNDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
SHOWERS AND THUNDERSTORMS WILL CONTINUE TO MOVE ACROSS OUR  
REGION THROUGH 0600Z WITH LINGERING SHOWERS ANTICIPATED LATE  
TONIGHT INTO PERHAPS WEDNESDAY MORNING.  
 
CONDITIONS WILL VARY BETWEEN VFR AND MVFR OVERNIGHT WITH  
LOCALIZED IFR IN PRECIPITATION. CLEARING AND VFR CONDITIONS  
ARE EXPECTED FOR WEDNESDAY.  
 
A SOUTHWEST WIND AROUND 8 TO 10 KNOTS WITH GUSTS NEAR 20 KNOTS  
IS EXPECTED TO BECOME WEST AT 5 TO 10 KNOTS OVERNIGHT, THEN  
NORTHWEST AT 5 TO 10 KNOTS FOR WEDNESDAY.  
 
OUTLOOK...  
WEDNESDAY NIGHT...VFR EXCEPT POSSIBLE MVFR OR IFR FOG PATCHES  
TOWARD DAWN THURSDAY WITH NEARLY CALM WIND.  
 
THURSDAY THROUGH SUNDAY...VFR. GENERALLY LIGHT WINDS FROM THE N  
OR NW, POSSIBLY BECOMING N-NE ON SATURDAY AND SUNDAY. SMALL  
CHANCE OF A LIGHT SHOWER VICINITY KABE/KTTN/KRDG THURSDAY  
AFTERNOON AND FRIDAY AFTERNOON.  
 

 
   
MARINE
 
 
STRENGTHENING SOUTHERLY FLOW IS ALLOWING SEAS TO GRADUALLY  
BUILD, WHICH SHOULD PEAK AROUND 3 TO 6 FEET ACROSS THE OCEAN  
WATERS AND 3 TO 4 FEET ACROSS THE DELAWARE BAY. STRONGEST GUSTS  
ARE EXPECTED THIS EVENING AROUND 25-30 KT, AND WILL GRADUALLY  
DIMINISH OVERNIGHT. SEAS WILL GRADUALLY SUBSIDE INTO WEDNESDAY  
AS A COLD FRONT MOVES THROUGH THE AREA AND THE PRESSURE GRADIENT  
BEGINS TO SUBSIDE.  
 
THERE WILL BE A CHANCE OF SHOWERS AND THUNDERSTORMS TONIGHT  
INTO TOMORROW AFTERNOON. THESE STORMS MAY LOCALLY REDUCE  
VISIBILITY AND PRODUCE WIND GUSTS TO NEAR GALE-FORCE.  
 
OUTLOOK...  
WEDNESDAY NIGHT THROUGH SATURDAY...WINDS AND SEAS BELOW SCA  
CRITERIA.  
 
SUNDAY...FOR NO SCA HEADLINE BUT CHANCE THAT NORTHEAST FLOW  
WILL INCREASE AND CAUSE HAZARDOUS SEAS TO DEVELOP ALONG THE S NJ  
AND DE COASTS SUNDAY (5 FEET).  
 
RIP CURRENTS...  
WEDNESDAY... LOW RISK, POSSIBLY BORDERING MODERATE BASED ON  
WHAT DEVELOPS THIS EVENING FOR RESIDUAL EFFECTS CARRYING INTO  
WEDNESDAY.  
 

 
   
CLIMATE
 
 
ATLANTIC CITY AND ALLENTOWN WERE WITHIN 2F OF RECORD TODAY.  
AROUND 91F FOR A MAX T.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR ANZ430-431-  
450>455.  
 

 
 

 
 
SYNOPSIS...DRAG  
NEAR TERM...IOVINO  
SHORT TERM...99  
LONG TERM...DRAG  
AVIATION...DRAG/IOVINO  
MARINE...DRAG/99  
CLIMATE...DRAG  
 
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