Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 280848
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
448 AM EDT TUE APR 28 2015

.SYNOPSIS...
A LARGE LOW PRESSURE SYSTEM OVER THE WESTERN NORTH ATLANTIC WILL
MOVE SLOWLY OUT TO SEA. A WEAK PRESSURE GRADIENT PREVAILS OVER THE
MID ATLANTIC STATES WEDNESDAY. LOW PRESSURE ALONG THE CAROLINA
COASTS STRENGTHENS AS IT MOVES NORTHEAST THURSDAY NIGHT AND FRIDAY.
HIGH PRESSURE MOVES IN FROM THE WEST LATER THIS COMING WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
ANOTHER FINE WEATHER DAY ACROSS THE MIDDLE ATLANTIC TODAY WITH HIGH
PRESSURE FROM THE WEST BUILDING ACROSS THE AREA. A DECENT PRESSURE
GRADIENT ACROSS THE AREA EARLY TODAY WILL RELAX DURING THE
AFTERNOON. UNDER MOSTLY SUNNY SKIES...TEMPERATURES WILL CLIMB INTO
THE LOW TO MID 60S ACROSS THE AREA. THESE READINGS WILL BE JUST A
FEW DEGREES BELOW NORMAL. WINDS WILL BE MOSTLY NORTH OR NORTHWEST
WINDS GUSTS AROUND 20 MPH THIS MORNING...THEN DECREASING WINDS BACK
TO 5 TO 10 MPH THIS AFTERNOON. ENJOY !

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
THE HIGH WILL CONTINUE TO INFLUENCE THE WEATHER TONIGHT. SKIES WILL
BE MAINLY CLEAR AND WINDS WILL BE LIGHT. LOW TEMPERATURES WILL DROP
INTO THE LOW 40S NORTH AND MID OR UPPER 40S ELSEWHERE.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
500 MB: BELOW NORMAL HEIGHTS PREVAIL IN OUR AREA THROUGH SATURDAY
MORNING AS ONE CLOSED LOW IN THE WESTERN ATLANTIC WEAKENS EASTWARD
WITH A NEW CLOSED LOW PROBABLY FORMING OVER THE MID ATLANTIC
STATES THURSDAY. IT DEPARTS INTO THE WESTERN ATLANTIC BY SATURDAY.
WARMER RIDGING SHOULD DEVELOP IN THE EASTERN UNITED STATES SUNDAY
AND PERSIST NEXT WEEK!

TEMPERATURES: THE MONTH AS A WHOLE IS NOW AVERAGING WITHIN A DEGREE
OF NORMAL THROUGH THE 27TH, EVER SO SLIGHTLY ON THE WARM SIDE OF
NORMAL. LITTLE CHANGE IS FORESEEN IN THE APRIL OUTCOME. CALENDAR DAY
AVERAGES SHOULD BE NEAR NORMAL WED-THU AND SATURDAY, MAYBE 2 TO 5
DEGREES BELOW NORMAL FRIDAY. A WARMING TREND WITH ABOVE NORMAL
TEMPERATURES SHOULD BEGIN SUNDAY AND CONTINUE NEXT WEEK.

FORECAST BASIS: UNLESS OTHERWISE NOTED, A 50 50 BLEND 00Z/28
GFS/NAM MOS GUIDANCE WEDNESDAY-WEDNESDAY NIGHT. THEN GFS MAVMOS
ONLY FOR THURSDAY, 00Z/28 MEX MOS THURSDAY NIGHT AND FRIDAY, THEN
THE 0521Z/28 WPC GRIDDED ELEMENTS OF MAX/MIN TEMP, 12 HOUR POP, 6
HOUR DEWPOINT- SKY-WIND FROM FRIDAY NIGHT THROUGH SUNDAY.

THE DAILIES...

WEDNESDAY...PARTLY CLOUDY.  NORTHWEST WIND GUSTS NEAR 15 MPH IN THE
AFTN. SEABREEZES COASTS? CONFIDENCE: ABOVE AVERAGE. THE ECMWF TSECTION
IS DRIER THAN THE GFS.

THEREAFTER: THE 00Z/28 NAM WAS PRETTY MUCH DISREGARDED AFTER 12Z
THURSDAY IN LIEU OF GEFS/ECEFS GUIDANCE-PATTERN.

REGARDING THE NEW GFS IMPLEMENTED EARLIER THIS YEAR.  WE ARE AWARE
OF ITS WET BIAS BUT ITS NOT ALWAYS SO. MULTI MODEL CHOICES
CONTINUE. ITS APPEARING TO ME THE GEFS IS A MORE RELIABLE PREDICTOR
THAN THE GFS OPERATIONAL MODEL (OPERATIONAL MORE VARIABLE AND
MAYBE WETTER BULLSEYES). THIS IS SIMILAR TO THE GGEM-NAEFS
APPROACH.

THE 00Z/28 GEFS TRENDED SLIGHTLY FURTHER EAST BUT STILL RATHER
ROBUST. ITS SO HARD TO BELIEVE WHEN YOU CHECK IT AGAINST THE
UK/GGEM/ECMWF. UNCERTAINTY IN THIS FORECAST CONTINUES.

THURSDAY AND FRIDAY...MOSTLY CLOUDY. GUSTY NE WIND 15-20 MPH
LATE THURSDAY AFTERNOON AND 20 TO 30 MPH FRIDAY. HAVE GENERALLY
MAINTAINED THE 330 PM MONDAY MOUNT HOLLY WFO FCST POPS AND TEMPS
FOR THIS PERIOD, DUE TO THE UNCERTAINTY. THE 00Z/28 GEFS AND NAEFS
STILL FCST 1/2 INCH OR GREATER SE PTN OF THE FA AND 6 HR PROBS
FOR .05 ARE VERY HIGH ON FRIDAY. 850 ENE INFLOW LOOKS TO BE -3SD
BUT IF THE GEFS CLOSED LOW VERIFIES MUCH WEAKER AS PER THE ECMWF,
THE SFC LOW WILL BE EAST AND MUCH WEAKER. TEMPS WERE CONTINUITY
MESHED WITH THE 00Z/28 2M 18Z THURSDAY AND FRIDAY FORECAST ECMWF
TEMPS.

SATURDAY...P/C. NW WIND GUSTY 20 MPH. THE EC HAS A CHANCE OF A
SHOWER.  SO CONFIDENCE: BELOW AVERAGE.

SUNDAY...P/C WITH A WEST WIND 10-15 MPH.  MILDER.   CONFIDENCE:
AVERAGE (EC DRIER THAN GFS)

MONDAY...P/C AND MILDER. THE 00Z/28 EC HAS A SHOWER RISK LATE.
LIGHT WIND. CONFIDENCE: BELOW AVERAGE.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

A LARGE SFC/UPPER AIR LOW WELL TO THE EAST AND HIGH PRESSURE WELL TO
THE WEST WILL KEEP A NORTHERLY FLOW ACROSS THE AREA TODAY. THE
PRESSURE GRADIENT WILL BE MODEST...SO SOME GUSTS OVER 20 KNOTS CAN
BE EXPECTED DURING THE MORNING AND AFTERNOON. SKY COVER...WHICH IS
MOSTLY BKN/OVC EARLY THIS MORNING SHOULD IMPROVE TO MOSTLY FEW/SCT
AFTER MIXING OCCURS SINCE THE LOWER LEVELS WILL BE TRENDING TOWARD
LOWER DEW POINTS. TONIGHT...LIGHTER WINDS AND MOSTLY SKC.

OUTLOOK...

WEDNESDAY...VFR. NORTHWEST WIND GUST AOB 15KT. LATE AFTERNOON
SEABREEZES COASTS? NEARLY CALM WIND AT NIGHT. CONFIDENCE: ABOVE
AVERAGE.

THURSDAY THROUGH FRIDAY....VFR CIGS WITH POSSIBLE MVFR/IFR CONDS IN
RAIN OR SHOWERS LATE THU INTO FRIDAY, ESPECIALLY KACY/KMIV/KILG.
SUSTAINED EAST TO NORTHEAST WIND AROUND 10 TO 15 KNOTS THURSDAY
AND FRIDAY IS EXPECTED ALONG WITH ITS POTENTIAL IMPACT ON
OPERATIONS AT KPHL. NORTHEAST WIND GUSTS 20 KT LATE THU AFTN AND
POSSIBLY 20-30 KT AT TIMES FRIDAY. CONFIDENCE: BELOW AVERAGE. THE
GFS AND ITS ENSEMBLES ARE ALONE ON THIS BLEAKER SCENARIO WHEREAS
OTHER TYPICALLY REVIEWED MODELS ARE NOT AS PESSIMISTIC ABOUT
A SIGNIFICANT WESTERN ATLANTIC LOW PRESSURE SYSTEM.

FRIDAY NIGHT AND SATURDAY...MAINLY VFR. CONFIDENCE BELOW AVERAGE
SINCE THE ECMWF HAS MODELED A CHANCE OF SHOWERS SATURDAY.

&&

.MARINE...
THE SCA FLAG ALREADY UP OVER THE WATERS WILL BE KEPT SINCE WIND
GUSTS PRESENTLY ARE AROUND 25 KTS AND THEY SHOULD CONTINUE INTO THE
MORNING. WIND GUSTS SHOULD DECREASE THIS AFTERNOON...SO WE WILL KEEP
THE NOON ENDING TIME THE SAME FOR NOW. SEAS SHOULD REMAIN 2 TO 4 FT
TODAY AND THE DECREASE TONIGHT. FAIR WEATHER EXPECTED TODAY AND
TONIGHT.

OUTLOOK...

WEDNESDAY THROUGH THURSDAY MORNING...NO MARINE HEADLINES ARE
ANTICIPATED.

THURSDAY AFTERNOON THROUGH FRIDAY...A SMALL CRAFT ADVISORY WILL
PROBABLY BE NEEDED FOR WIND GUSTS OF 25 TO 30 KNOTS AND FOR WAVES
ON OUR OCEAN WATERS IN EXCESS OF 5 FEET...POSSIBLY 7 TO 10 FEET
FRIDAY. THE WIND DIRECTION IS ANTICIPATED TO BACK GRADUALLY FROM
THE EAST TO THE NORTH. THERE IS STILL THE POTENTIAL FOR GALE
FORCE NORTHEAST TO NORTH GUSTS ON FRIDAY.

FRIDAY NIGHT AND SATURDAY...WIND SPEEDS ARE FORECAST TO REMAIN
BELOW THE SMALL CRAFT ADVISORY CRITERION. HOWEVER, WAVE HEIGHTS ON
OUR OCEAN WATERS SHOULD REMAIN AROUND OR ABOVE 5 FEET...POSSIBLY 7
FEET OR MORE EAST OF DELAWARE.

&&

.FIRE WEATHER...
MARGINAL RED FLAG CONDITIONS ACROSS THE AREA TODAY. THE GREATEST
WIND GUSTS WILL BE THIS MORNING...WHILE THE LOWERS RH VALUES
(LOW/MID 30S PCT) WILL BE THIS AFTERNOON. WE WILL HOLD OFF ON ANY
SPS FOR NOW. THE DAY SHIFT MAY CONTACT THE FIRE WX PARTNERS FOR
FURTHER ACTION IF NEEDED.

&&

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

&&

$$
SYNOPSIS...DRAG
NEAR TERM...O`HARA
SHORT TERM...O`HARA
LONG TERM...DRAG 447A
AVIATION...DRAG/O`HARA
MARINE...DRAG/O`HARA
FIRE WEATHER...



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