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 152244
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
644 PM EDT WED MAY 15 2013

.SYNOPSIS...
AN AREA OF LOW PRESSURE WILL SLIDE THROUGH SOUTHERN CANADA TONIGHT.
A WARM FRONT WILL LIFT THROUGH THE AREA THIS EVENING, FOLLOWED BY A
COLD FRONT OVERNIGHT. THIS FRONT 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.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
-- Changed Discussion --
AN IMPULSE MOVING DOWN THE EASTERN SIDE OF A SHALLOW RIDGE AND IN
THE NORTHERN PORTION OF THE SPLIT FLOW SHOULD CLEAR THE AREA BY OR
SHORTLY AFTER 00Z. AN ASSOCIATED SURFACE WARM FRONT SHOULD FOLLOW
SUIT. SCATTERED SHOWERS AND A FEW TSTMS HAVE DEVELOPED ACROSS SRN
PA WHICH ARE QUICKLY HEADING E/SE. THEY WILL WEAKEN AS THEY MOVE
ACROSS NE MD/NRN DE OVER THE NEXT FEW HOURS. POP GRIDS HAVE BEEN
ADJUSTED SLIGHTLY.

CONTINUED WITH TEMPS AS PER PREVIOUS FCST.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
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.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
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.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
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 18Z TAFS.
SOME SHOWER ACTIVITY IS POSSIBLE INTO THE EVENING, BUT WE AGAIN
DIDN`T HIT THAT VERY HARD. A MODERATE SOUTH TO SOUTHWEST WIND WITH
SOME GUSTINESS (ESPECIALLY REMOVED FROM THE NORTHWESTERN SITES)
SHOULD LINGER INTO THE EVENING, BUT THEN WINDS 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.

&&

.MARINE...
A STRONG LOW LEVEL JET IS FORECAST TO MOVE ACROSS THE WATERS FROM
LATE THIS AFTERNOON THROUGH THIS EVENING, AND THE SMALL CRAFT
ADVISORY CONDITIONS (WHICH HAVE BEEN SLOW TO DEVELOP) SHOULD COME TO
PASS AT THAT TIME. CONDITIONS WILL THEN 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.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 AM EDT THURSDAY FOR ANZ450>455.
     SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ431.

&&

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