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Area Forecast Discussion
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000
FXUS61 KPHI 281111
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
611 AM EST SUN DEC 28 2014

.SYNOPSIS...
LOW PRESSURE MOVING ACROSS QUEBEC TODAY WILL CAUSE A COLD FRONT TO 
CROSS OUR AREA. THE FRONT WILL MOVE WELL TO THE SOUTH TONIGHT AND 
MONDAY...WHILE A WEAK AREA OF LOW PRESSURE MOVES ALONG IT MONDAY AND 
MONDAY NIGHT. HIGH PRESSURE WILL RIDGE ACROSS THE REGION TUESDAY AND 
REMAIN IN CONTROL OF THE WEATHER THROUGH FRIDAY. A LOW PRESSURE 
SYSTEM AND FRONT MAY ADVANCE TOWARD OUR AREA NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THIS ESTF UPDATE WE UPPED POPS FOR FASTER MOVEMENT OF THE FIRST
SURGE IN OUR AREA. WE LOWERED POPS CLOSE TO MID DAY TO ACCOUNT FOR
A POSSIBLE BREAK AND THEN RAISED THEM AGAIN DURING THE AFTERNOON FOR
THE SECOND SURGE.  

THE WRF-NMMB INITIALIZATION LOOKED BETTER THAN THE GFS AT 500MB WHILE 
AT 850MB AND 925MB BOTH MODELS WERE SIMILAR. WITH THE LATTER PAIR 
THERE WAS A COLD INITIALIZATION BIAS WHICH WAS TAKEN INTO 
CONSIDERATION FOR TONIGHT. THROUGH 06Z THE GFS SEEMED TO BE 
VERIFYING THE CLOSEST WITH PCPN PLACEMENT AND AMOUNTS, WITH THE 
ECMWF SECOND AND OTHERS LAGGING FURTHER. WRF-NMMB ALREADY HAD SOME 
NORTHWEST BIASES. BECAUSE OF THE MONDAY NIGHT INTO TUESDAY FLIPS 
THAT THE GFS AND WRF-NMMB HAVE HAD, THIS PACKAGE DOES LEAN MORE 
HEAVILY THE ECMWF'S WAY WHICH HAS BEEN THE MOST CONSISTENT MODEL. 

THE BRIEF RUN OF SUNNY WEATHER HAS ENDED FOR OUR AREA. FOR TODAY, WE 
SEE TWO IMPULSES REFLECTED IN THE MODEL FIELDS THAT WILL AFFECT OUR 
AREA. ONE WAS INITIALLY IN THE OHIO VALLEY LAST EVENING, THE SECOND 
CURRENTLY IN WESTERN KY. THAT FIRST IMPULSE WILL MAINLY AFFECT THE 
NORTHWESTERN PART OF OUR CWA THROUGH THE FIRST HALF OF TODAY. HERE 
WE ARE SEEING THE BEST CONFLUENCE OF RELATIVE INSTABILITY, PWAT AND 
PROX TO THE ENTRANCE REGION OF THE JET. SO THIS LOCALE HAS THE 
HIGHEST CHANCE RELATIVE TO GUIDANCE OF SEEING SOME HEAVIER AMOUNTS. 
THE SECOND IMPULSE OVER KENTUCKY IS SLATED TO ARRIVE IN THE SERN 
HALF OF OUR CWA THIS AFTERNOON AS THE CDFNT COMPLETES ITS PASS 
THROUGH OUR CWA. (11Z IT IS NEARING PITTSBURGH) HIGHEST POPS
SLIDE SOUTHEASTWARD AS THE DAY PROGRESSES AND WE END SHOWER
CHANCES NORTHWEST DURING THE AFTERNOON. IN REALITY PCPN STARTS
HAVING AN UNDER-RUNNING LOOK TO IT DURING THE AFTERNOON, BUT WE
WAITED UNTIL TONIGHT TO CONVERT THE SHOWERS TO RAIN TO KEEP
FORMATTED PRODUCTS A LITTLE LESS CLUTTERED.

MAX TEMPS ARE A STAT GUIDANCE BLEND. GIVEN TIMING OF PCPN WE MAY BE 
TOO WARM NORTHWEST AND TOO COLD SOUTHEAST. WINDS OVERALL SHOULD BE 
ON THE LIGHT SIDE, EVEN IN THE POST CDFNTL AIR MASS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
THE NEXT IMPULSE TO BRING PCPN CHANCES INTO OUR AREA IS EMANATING 
FROM THE WESTERN GULF OF MEXICO. GIVEN ITS LONG TREK TO GET HERE AND 
TO FACTOR IN A BIT OF UNCERTAINTY, WE COMPROMISED BETWEEN THE GFS 
AND ECMWF DURING THIS TIME PERIOD. SO ONCE PCPN ASSOCIATED WITH 
IMPULSE NUMBER TWO EXITS, A STEADY RAIN IS MOST LIKELY TO OCCUR 
LATER AT NIGHT IN DELMARVA FROM IMPULSE NUMBER THREE. GIVEN THE COLD 
BIAS INITIALIZATION (ALSO LOCATION/MOVEMENT OF THE JET), WE SIDED 
WITH WARMER THERMAL FIELDS OVERNIGHT. PTYPE IS ALL LIQUID AND WE 
THINK THE GFS HINT OF SOME SLEET (ADVECTING IN SUB ZERO 925MB AIR) 
HAD TOO FAST OF A HEAD START TO OCCUR. SKIES SHOULD BECOME CLEARER 
(OR AT THE LEAST CLOUDS HIGHER) IN THE NORTHERN PART OF OUR CWA. MIN 
TEMPERATURES ARE GENERALLY AT OR ABOVE STAT GUIDANCE. LOWEST 
CONFIDENCE NORTHWEST WHERE SOME SKIES MIGHT CLEAR.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
THE FRONT FROM THE NEAR/SHORT TERM PARTS OF THE FCST WILL HAVE
SETTLED WELL SOUTH OF THE AREA MONDAY. MOST OF THE MODELS SHOW
SOME WEAK WAVE DEVELOPING ALONG IT AND CRUISING BY TO THE SOUTH
MONDAY. THE PREFERRED EC/GFS MODELS SOME SOME LIGHT QPF ACROSS THE
DELMARVA MONDAY MORNING...SO WE HAVE GONE ALONG WITH THAT...BUT
REDUCED POPS/QPF FROM YESTERDAYS FCST. THE TREND IN MOST MODELS
HAS BEEN TO SUPPRESS THE SYSTEM. THE 00Z NAM REMAINS NORTH WITH THE
QPF/HIGHER POPS. THE WPC CONSIDERS THE NAM AN OUTLIER SOLUTION...
SO WE ARE GOING TO DISREGARD THAT FOR NOW.

TUE THRU FRI...HIGH PRESSURE OVER THE PLAINS AND MIDWEST BRINGS
COLDER AND DRY AIR TO THE REGION. TEMPERATURES WILL FALL TO A FEW
DEGREES BELOW NORMAL TUE AND REMAIN AT OR BELOW NORMAL THRU
FRIDAY. A SLGT CHC FOR A SNOW SHOWER ACROSS THE DELMARVA EARLY
TUE...BUT OTHER THAN THAT A DRY FCST FOR THE PERIOD. 

FRI NIGHT/SAT...THE OP MODELS SHOWING ANOTHER LOW DEEPENING AND
MOVING WEST OF THE AREA. CLOUDS WILL INCREASE FRI AND PCPN WILL
OVERSPREAD THE AREA FRI NIGHT AND REMAIN INTO SAT. TEMPS COULD BE
COLD ENOUGH FOR SOME SNOW/MIXED PRECIP FRI NIGHT...BUT READINGS
WILL PROBABLY WARM ENOUGH FOR MOSTLY RAIN SAT.

&&

.AVIATION /11Z SUNDAY THROUGH THURSDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

12Z TAFS CONTINUE TO CONTAIN MVFR CONDITIONS MAINLY DURING MORE
FREQUENT SHOWERS.
 
THIS MORNING AND AFTERNOON...NORTHERN AIRPORTS AND TERMINALS VFR
SHOWERS ARE ONGOING TERMINALS WITH CIGS LOWERING TO MVFR LATER IN
THE MORNING. VFR CIG IMPROVEMENT DURING THE AFTERNOON AS SHOWERS 
DECREASE AND END.

KPHL AREA AIRPORTS AND TERMINALS/AIRPORTS TO THE SOUTH/SOUTHEAST 
EXPECTING A VFR CIG MORNING WITH SPOTTIER MORNING SHOWERS AND 
MORE WIDESPREAD SHOWERS DURING THE AFTERNOON. MVFR CIGS ARE
POSSIBLE DURING THE AFTERNOON.

ALL TERMINALS VSBY RESTRICTIONS TOO BRIEF TO INCLUDE, MAINLY VFR
VSBYS. WINDS WILL BECOME WEST TO NORTHWEST DURING THE LATE MORNING
TO EARLY AFTERNOON AS THE COLD FRONT MOVES THROUGH. SPEEDS SHOULD
BE LESS THAN 10 KNOTS.

TONIGHT, VFR MID LEVEL CIGS RISING TO CIRRUS LEVELS AT NORTHERN
AIRPORTS. NORTHWEST TO NORTH WINDS AVERAGING 5 TO 10 KNOTS.
SOUTHERN TERMINALS AND DELMARVA AIRPORTS MIGHT SEE A SECOND SURGE
OF MAINLY VFR RAIN LATE AT EVENING AND OVERNIGHT.
  
OUTLOOK...
MONDAY THRU EARLY TUESDAY...VFR NORTH. LOWER CONDITIONS POSSIBLE
IN PCPN AND LOWER CLOUDS SOUTH. 

TUESDAY AFTERNOON THRU THURSDAY...VFR EXPECTED.

&&

.MARINE...
SUB SMALL CRAFT ADVISORY CONDITIONS ARE PREDICTED THROUGH TONIGHT. 
THE SURGE OF STRONGER SOUTHWEST WINDS ALOFT THIS MORNING IS NOT 
MIXING DOWN AS HIGHEST OBSERVED WINDS ARE AROUND 15 KT. THE AIR 
TEMPERATURE/WATER TEMPERATURE DIFFERENTIAL IS NOT GOING TO IMPROVE 
THIS MORNING FOR MIXING AND BY THIS AFTERNOON, THE WIND FIELDS ALOFT 
ARE LIGHTER. THUS A CDFNTL PASSAGE DURING THE AFTERNOON WILL BRING 
SHOWERS, BUT NOT STRONGER WINDS TO THE AREA WATERS.

WINDS WILL VEER TO A NORTHERLY PUSH BEHIND THE COLD FRONT TONIGHT, 
BUT THE OVERALL PRESSURE GRADIENT WILL REMAIN RELATIVELY WEAK AND 
EVEN WITH A BETTER AIR/WATER TEMPERATURE DIFFERENTIAL, SUB SMALL 
CRAFT ADVISORY CONDITIONS ARE PREDICTED TO CONTINUE. 
  
OUTLOOK...
MON...MOSTLY SUB-SCA CONDITIONS. 
MON NIGHT/TUE...SCA CONDITIONS POSSIBLE. 
TUE NIGHT THRU THU...MOSTLY SUB-SCA CONDITIONS EXPECTED.

&&

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

&&

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






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