National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 160440
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1240 AM EDT THU MAY 16 2013

.SYNOPSIS...
-- Changed Discussion --
AN AREA OF LOW PRESSURE WILL SLIDE THROUGH SOUTHERN CANADA
TONIGHT. A FRONTAL BOUNDARY ACROSS OUR REGION WILL SAG TO OUR
SOUTH THURSDAY, BEFORE A SECOND COLD FRONT MOVES THROUGH THE AREA
THURSDAY NIGHT. THIS BOUNDARY IS EXPECTED TO STALL TO OUR SOUTH
THROUGH THE WEEKEND INTO EARLY MONDAY AS HIGH PRESSURE BUILDS
SOUTH OUT OF CANADA AND ACROSS THE NORTHEAST. AS THE HIGH BUILDS
TO OUR SOUTHEAST TUESDAY, THE FRONT IS EXPECTED TO RETURN
NORTHWARD AS A WARM FRONT.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
-- Changed Discussion --
A FRONTAL BOUNDARY EXTENDED ACROSS SOUTHWESTERN AND SOUTH CENTRAL
PENNSYLVANIA TO THE UPPER DELMARVA AND EXTREME SOUTHERN NEW JERSEY
SHORTLY AFTER MIDNIGHT. TEMPERATURES WERE MAINLY IN THE 70S TO THE
SOUTH OF THE FRONT AND IN THE 60S AND 50S TO THE NORTH. ISOLATED
SHOWERS WERE CONTINUING TO RIDE EASTWARD ALONG THE BOUNDARY.
HOWEVER, THEY WERE DIMINISHING GRADUALLY AND THAT TREND SHOULD
CONTINUE. WE HAVE REMOVED ANY MENTION OF PRECIPITATION FROM OUR
FORECAST FOR THE OVERNIGHT PERIOD.

ANOTHER FRONTAL BOUNDARY EXTENDED ACROSS FAR NORTHERN
PENNSYLVANIA, SOUTHEASTERN NEW YORK AND SOUTHERN NEW ENGLAND. THE
BOUNDARY IS EXPECTED TO DROP INTO THE NORTHERN PART OF OUR
FORECAST AREA OVERNIGHT. IT MAY BRING A FEW CLOUDS BUT NO
PRECIPITATION.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TODAY/...
-- Changed Discussion --
THE FRONTAL BOUNDARY IS FORECAST TO STALL TO OUR SOUTH, AND THEN
SOME ENERGY IN THE FAST SPLIT FLOW LOOKS LIKE IT WILL MOVE ALONG
THE BAROCLINIC ZONE. OUR FORECAST CARRIES CHANCE TO SLIGHT CHANCE
POPS SOUTH AND DRY WEATHER NORTH. THERE LOOKS LIKE THERE IS ENOUGH
INSTABILITY TO CONTINUE WITH THE MENTION OF THUNDER, BUT THERE
DOESN`T SEEM TO BE ANY CONCERN REGARDING SEVERE WEATHER (THE BEST
SHEAR IS NORTH, AND THE CAPES SOUTH AREN`T THAT ROBUST). IT LOOKS
LIKE WE WILL MIX TO H925, AND GUIDANCE/CONTINUITY AND H925
TEMPERATURES ALL SUPPORT THE MAX TEMPERATURE FORECAST.
-- End Changed Discussion --

&&

.LONG TERM /TONIGHT THROUGH WEDNESDAY/...
-- Changed Discussion --
A WEAK FRONTAL BOUNDARY WILL MOVE THROUGH THE AREA THURSDAY
EVENING AND SOUTH OF THE AREA INTO THE OVERNIGHT HOURS. THERE
REALLY ISN`T MUCH MOISTURE WITH THE FRONT, SO WE DO NOT EXPECT ANY
PRECIPITATION ASSOCIATED WITH THIS FRONT. HOWEVER, THERE COULD BE
SOME SHOWERS OR THUNDERSTORMS ACROSS OUR SOUTHERN AREAS WHERE
THERE IS SOME HIGHER MOISTURE FORECAST AS WELL AS SOME LIFT
ASSOCIATED WITH A WEAK DISTURBANCE MOVING THROUGH. ANY SHOWER
ACTIVITY SHOULD DISSIPATE OVERNIGHT.

FRIDAY INTO FRIDAY NIGHT IS EXPECTED TO BE DRY FOR MUCH OF THE
AREA AS HIGH PRESSURE BEGINS TO TRY TO NOSE ITS WAY DOWN ACROSS
OUR AREA FROM THE NORTH. OUR SOUTHERN AREAS ACROSS THE DELMARVA
MAY HAVE SOME ISOLATED SHOWERS DEVELOP LATE IN THE DAY AS A WEAK
DISTURBANCE MOVES THROUGH THE AREA. THERE MAY BE JUST ENOUGH
MOISTURE IN THIS AREA FOR A FEW SHOWERS TO DEVELOP, SO WE WILL
KEEP A SLIGHT CHANCE IN FOR NOW.

AS WE MOVE INTO SATURDAY, HIGH PRESSURE BUILDS ACROSS THE
NORTHEAST AND ACROSS THE NORTHEAST COAST. THIS WILL SET UP AN
EAST/SOUTHEASTERLY FLOW ACROSS THE AREA. AN INCREASE IN CLOUD
COVER IS EXPECTED, WHICH WILL LIKELY KEEP TEMPERATURES IN CHECK
SATURDAY. AS WE MOVE THROUGH THE DAY, A SHORT WAVE IS CURRENTLY
FORECAST TO MOVE TOWARD THE AREA DURING THE DAY. THIS COULD LEAD
TO SOME SHOWER ACTIVITY. HOWEVER, CONFIDENCE IS NOT HIGH ON THIS
OCCURRING, SO ONLY A 20/30 POP IS INCLUDED AT THIS TIME.

A STATIONARY BOUNDARY WILL BE LOCATED TO OUR SOUTH FROM SATURDAY
NIGHT THROUGH TUESDAY. THE MAIN QUESTION WITH THIS FORECAST UPDATE
IS WHERE THE LOCATION OF THE BOUNDARY WILL BE AND IF ANY IMPULSES
OR WEEK LOW PRESSURE SYSTEMS WILL TRAVERSE IT.

SATURDAY NIGHT THE FRONT WILL BE LOCATED SOUTH OF THE REGION AND
HAVE KEPT SKIES MOSTLY CLOUDY AND RAIN CHANCES LOW TO SLIGHT
ACROSS THE REGION. BY SUNDAY THE 12Z GFS HAS A IMPULSE MOVING
THROUGH THE REGION WHILE THE ECMWF IS FARTHER SOUTH WITHOUT AN
IMPULSE MOVING ALONG THE BOUNDARY. THE GFS SOLUTION WOULD MEAN
RAIN MOST OF THE DAY ON SUNDAY WHILE THE 00Z EC SOLUTION WOULD
KEEP THE REGION DRY. THE CMC ALONG WITH SEVERAL OTHER GFS ENSEMBLE
MEMBERS DO SUGGEST THE CHANCE FOR SHOWERS. SO HAVE KEPT A CHANCE
POP IN THE FORECAST, DID NOT INCLUDE THUNDER WITH A LACK OF
INSTABILITY EXPECTED. WENT AWAY FROM THE VERY HIGH QPF AMOUNTS ON
THE 12Z GFS AS WELL MORE IN LINE WITH A GENERIC LIGHT RAINFALL IF
IT DOES OCCUR, FOCUSED IN THE SOUTH. TEMPERATURE FORECAST ALSO
REFLECTS LEANING TOWARD A DRIER OUTCOME ATTM.

FOR MONDAY AND TUESDAY THE BOUNDARY IS EXPECTED TO MOVE THROUGH
THE REGION AS A WARM FRONT. THE EXACT LOCATION AND TIMING OF THIS
FRONT WILL HAVE AN IMPACT ON OUR SENSIBLE WX WITH A WIND SHIFT AND
CONTINUED LOW CHANCES OF PRECIPITATION. INSTABILITY WILL AT LEAST
BECOME MARGINAL ALLOWING FOR A CHANCE OF THUNDER AS WELL DURING
THE DAY. WENT LOWER THAN GUIDANCE WITH DEWPOINTS IN THESE PERIODS
MAINLY DUE TO THE POTENTIAL FOR MOISTURE ADVECTION TO BE LOWER
THAN MODELED.

ON WEDNESDAY CONFIDENCE INCREASES THAT WE WILL BE IN THE WARM
SECTOR IF THE BOUNDARY. THIS SHOULD RESULT IN A PERIOD WHERE THE
SKIES COULD CLEAR OUT SOME FROM A MAINLY CLOUDY SKY EARLIER IN THE
WEEK. 850 MB TEMPS WILL ALSO BE AROUND 15C DURING THE DAY COUPLED
WITH A STRONG SOUTHERLY FLOW THE POTENTIAL EXISTS FOR MANY AREAS
TO GET INTO THE 80`S. THE 12Z MODELS HAVE COOLED OFF SOME BUT IF
WE GET FIRMLY INTO THE WARM SECTOR WITH RAIN HOLDING OFF TILL
LATER IN THE DAY THE WARMER TEMPERATURES ARE POSSIBLE. TIMING
UNCERTAINTIES REGARDING THE MAIN COLD FRONTAL BOUNDARY. RIGHT NOW
HAVE INTRODUCED LOW CHANCE POPS AS THAT ASPECT CAN BE FINE TUNED
WITH LATER UPDATES.
-- End Changed Discussion --

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

THE FORECAST GENERALLY IS A VFR FORECAST THROUGH THURSDAY. SOME
FOG IS POSSIBLE TONIGHT, BUT WE PLAYED IT DOWN IN THE TAFS. THE
WIND SHOULD VEER TO NORTHWEST AND DIMINISH.

SHOWER OR TSTM ACTIVITY ON THURSDAY LIKELY WILL REMAIN TO THE
SOUTH OF THE TAF SITES, AND WINDS SHOULD BE FAIRLY GENTLE OUT OF
THE WEST TO NORTHWEST. SOME MID AND HIGH CLOUDS AND A FEW CUMULUS
ARE FORECAST.


OUTLOOK...
THURSDAY NIGHT-FRIDAY NIGHT...MOSTLY VFR. SHOWERS POSSIBLE SOUTH
OF PHL.

SATURDAY...MOSTLY VFR...EASTERLY FLOW MAY CONTRIBUTE TO LOWER
CLOUDS; ALTHOUGH THIS IS LOW CONFIDENCE. POSSIBLE SHOWERS IN THE
AFTERNOON.

SATURDAY NIGHT ..... MAINLY VFR WITH A SLIGHT CHANCE OF SHOWERS
AND SOUTH TO SOUTHEAST WINDS AROUND 5 KNOTS.

SUNDAY AND MONDAY MAINLY VFR EXPECTED ATTM WITH SCATTERED SHOWERS
WITH SOUTHEAST WINDS 5 TO 10 KNOTS.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
MARGINAL SCA CONDITIONS CONTINUE ALONG THE OCEAN SHORE AREAS.
CONDITIONS WILL RETURN TO SUB-ADVISORY BY OR SHORTLY AFTER
DAYBREAK AND REMAIN THAT WAY THROUGH THE REST OF THURSDAY.

OUTLOOK...
WINDS AND WAVES ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS FROM
THURSDAY NIGHT THROUGH SATURDAY.

SEAS ARE EXPECTED TO STAY BELOW SCA LEVEL FROM SATURDAY NIGHT
THROUGH 12Z MONDAY ATTM. SCA CONDITIONS WILL BE POSSIBLE ON
MONDAY. OVERALL WAVEWATCH GUIDANCE MAY BE HIGH ON SEAS WENT MORE
IN THE DIRECTION OF USING WIND SPEED FOR WAVE HEIGHTS.
-- End Changed Discussion --

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 AM EDT THIS MORNING FOR
     ANZ450>455.
-- End Changed Discussion --

&&

$$

SYNOPSIS...GAINES/ROBERTSON
NEAR TERM...IOVINO
SHORT TERM...DELISI
LONG TERM...GAINES/ROBERTSON
AVIATION...DELISI/GAINES/ROBERTSON
MARINE...DELISI/GAINES/ROBERTSON