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Area Forecast Discussion
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000
FXUS61 KPHI 210124
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
924 PM EDT WED AUG 20 2014

.SYNOPSIS...
WEAK LOW PRESSURE WILL MOVE NORTH OF THE AREA TONIGHT AND THURSDAY. 
ANOTHER LOW PRESSURE SYSTEM WILL MOVE SOUTH OF THE AREA THURSDAY 
NIGHT THROUGH EARLY SATURDAY. HIGH PRESSURE WILL BUILD IN FROM THE 
NORTH LATER FRIDAY, THEN REMAIN FOR THE WEEKEND AND INTO EARLY NEXT 
WEEK.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A SHORT WAVE TROUGH AHEAD OF A CLOSING OFF UPPER-LEVEL TROUGH 
DROPPING DOWN ACROSS THE GREAT LAKES REGION WILL LIFT 
EAST-NORTHEASTWARD THROUGH TONIGHT. THE AIRMASS ACROSS OUR AREA IS 
MORE STABLE, HOWEVER ENOUGH MOISTURE COMBINED WITH SOME FORCING 
SHOULD RESULT IN A FEW SHOWERS THROUGH THE NIGHT. THIS MAY OCCUR 
ESPECIALLY LATE AS ANOTHER SHORT WAVE APPROACHES FROM THE NORTHWEST. 
ANY MAINLY ISOLATED LINGERING SHOWERS THIS EVENING APPEARS TO BE 
TIED TO WEAK CONVERGENCE ALONG THE WEAKENING INSTABILITY GRADIENT. 
WE WILL THEREFORE KEEP SOME LOW POPS IN FOR MOST PLACES AS A FEW 
CELLS COULD POP NEARLY ANYWHERE. THE HIGHER POPS THOUGH WERE 
MAINTAINED ACROSS THE NORTHWESTERN AREAS ESPECIALLY LATE, AS THESE 
LOCALES ARE CLOSER TO THE INCOMING SHORT WAVE AND SOME HEIGHT FALLS. 
THE INSTABILITY LOOKS LOW ENOUGH, THEREFORE DID NOT INCLUDE THUNDER
ATTM.

OTHERWISE, ENOUGH MOISTURE AND THE LEFTOVER DEBRIS CLOUDS SHOULD 
RESULT IN MORE CLOUDINESS THROUGH THE NIGHT FOR MOST LOCALES. THE 
HOURLY GRIDS WERE TWEAKED BASED ON THE LATEST OBSERVATIONS AND THEN 
THE LAMP/LAV GUIDANCE WAS BLENDED IN TO HELP ASSIST WITH TRENDS. NO 
CHANGES WERE MADE TO THE LOW TEMPERATURES ATTM.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
THURSDAY...ANOTHER SHORT WAVE IN THE WNW FLOW OVER SOUTHERN NEW
YORK STATE SHOULD REDEVELOP HEAVY CONVECTION DURING THE AFTN OVER
E PA...POSSIBLY EXTENDING INTO W NJ AND THE MD E SHORE CLOSER TO THE
CONVERGENCE OF THE SFC LOW AND INVERTED TROUGH EXTENDING NWD FROM
THE VCNTY OF DCA. PWAT VALUES ARE GENERALLY FORECAST AROUND
1.5-1.75 INCHES, SO SOME SHOWERS/STORMS COULD PRODUCE A PERIOD OF
MODERATE TO HEAVY RAINFALL. ISOLATED SMALL HAIL NOT IMPOSSIBLE AS
TT NEAR 50 IN AREA OF MAX INSTABILITY IN NJ (NEAR THE DELAWARE
RIVER).

FORECAST BASIS: POPS WERE BLENDED NCEP MOS POPS WITH THE 09Z SREF AND
THAT GIVES THE BEST CHANCE FOR SOME NEEDED RAIN TO E PA. OTRW A 50
50 BLEND OF 12Z/20 NCEP MOS EXCEPT BLENDED RGEM SKY WITH NAM SKY
AND GFS MOS GUIDE.

NEAR OR SLIGHTLY ABOVE NORMAL TEMPS.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
THE LONG TERM FORECAST STARTS OFF WITH RAIN CHANCES, BEFORE A DRYING 
OUT PERIOD SETS IN ACROSS THE AREA.

THE WEAK AREAS OF LOW PRESSURE TO THE NORTH (THU NIGHT AND
FRIDAY) AND THE SOUTH (FRIDAY THRU SATURDAY) WILL FORCE US TO KEEP
LOW CHC POPS OR SLGT CHC POPS FOR THOSE PERIODS. THE SYSTEMS DO
NOT LOOK STRONG ENOUGH TO PRODUCE ANY HEAVY RAINS HOWEVER. DRY
WEATHER IS EXPECTED FOR SUNDAY INTO EARLY NEXT WEEK. HIGH PRESSURE
WILL BUILD IN FROM THE NORTH/NORTHEAST ALLOWING DRY AIR TO
OVERSPREAD THE AREA. 

TEMPERATURES THROUGH THE LONG RANGE WILL START NEAR NORMAL
FRIDAY...BEFORE DROPPING TO BELOW NORMAL FOR THE WEEKEND AND NEXT
MONDAY. READINGS WILL REBOUND BACK TO NEAR NORMAL NEXT TUESDAY AND
THEN POSSIBLY GO ABOVE NORMAL WEDNESDAY.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

OVERNIGHT...VFR OVERALL WITH CEILINGS AT OR ABOVE 4000 FEET. A FEW 
SHOWERS SHOULD BE AROUND ESPECIALLY NORTH AND WEST OF KPHL. 
SOUTHERLY WINDS 5-8 KNOTS DIMINISHING TO UNDER 5 KNOTS. THERE COULD 
BE SOME LOCALIZED MVFR CEILINGS WITH FOG TOWARD DAYBREAK, ESPECIALLY 
IF THE CLOUDS THIN FOR A LONG ENOUGH PERIOD OF TIME.

THURSDAY...GENERALLY VFR CEILINGS. SOME SHOWERS AND THUNDERSTORMS 
ARE EXPECTED TO OCCUR ESPECIALLY FARTHER INLAND, WHICH MAY LOWER 
CEILINGS AND VISIBILITIES TO BRIEFLY IFR. THE GREATEST CONCENTRATION 
OF SHOWERS AND STORMS MAY BE IN PORTIONS OF EASTERN PENNSYLVANIA 
DURING THE AFTERNOON. SOUTHERLY WINDS GENERALLY 5-10 KNOTS,
ALTHOUGH POTENTIALLY LOCALLY GUSTY BRIEFLY WITH A THUNDERSTORM.

OUTLOOK...
THU NIGHT THRU SATURDAY...MOSTLY VFR. SHOWERS WITH LOWER
CONDITIONS ARE POSSIBLE. 

SAT NIGHT THRU MONDAY...MOSTLY VFR.

&&

.MARINE...
NO MARINE RELATED HEADLINES THROUGH THURSDAY.

EAST-SOUTHEAST WINDS BETWEEN 5-15 KT.

OUTLOOK...
THU NIGHT THRU FRI NIGHT...SUB SCA CONDITIONS W/ SCT SHOWERS. 
SAT THRU MON...LOW END SCA SEAS EXPECTED ON THE OCEAN. MOSTLY FAIR WX.

&&

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

&&

$$
SYNOPSIS...O'HARA
NEAR TERM...GORSE
SHORT TERM...DRAG
LONG TERM...O'HARA
AVIATION...GORSE/O'HARA
MARINE...DRAG/O'HARA




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