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 170731
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
331 AM EDT FRI MAY 17 2013

.SYNOPSIS...
-- Changed Discussion --
A FRONTAL BOUNDARY WILL REMAIN STALLED TO OUR SOUTH THROUGH THE
WEEKEND. THE BOUNDARY IS THEN FORECAST TO SLOWLY LIFT NORTHWARD AS A
WARM FRONT TUESDAY INTO WEDNESDAY. LOW PRESSURE AND ITS ASSOCIATED
COLD FRONT ARE FORECAST TO APPROACH OUR AREA FROM THE WEST
WEDNESDAY, THEN MOVE THROUGH OUR REGION WEDNESDAY NIGHT AND THURSDAY.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
A MID LEVEL RIDGE WILL BE LOCATED OVER THE MIDDLE PART OF THE
COUNTRY TODAY, KEEPING OUR REGION UNDER A NORTHWEST FLOW. DRY
WEATHER CONDITIONS ARE EXPECTED. WE MAY SEE SOME CIRRUS FROM THE
NORTHWEST PASS OVERHEAD AT TIMES. ALSO, MID LEVEL CLOUDS MAY SKIRT
OUR FAR SOUTHERN COUNTIES. NEVERTHELESS, OUR ENTIRE FORECAST AREA
WILL LIKELY RECEIVE A GOOD AMOUNT OF SUNSHINE FOR TODAY.

A NORTHWEST TO NORTH SURFACE FLOW IS FORECAST TO PERSIST INTO THE
MID AFTERNOON. THE FLOW IS EXPECTED TO WEAKEN AND IT SHOULD ALLOW A
SEA BREEZE FRONT TO MAKE ITS WAY ACROSS THE COASTAL PLAIN FROM ABOUT
MID AFTERNOON INTO THE EARLY EVENING.

MAXIMUM TEMPERATURES ARE ANTICIPATED TO BE MAINLY IN THE 70S FOR
TODAY. WE HAVE FAVORED THE HIGH END OF THE GUIDANCE AS THE SUNSHINE
WILL LIKELY WARM THE DRY AIR RATHER EFFICIENTLY.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
-- Changed Discussion --
OUR REGION WILL REMAIN UNDER A NORTHWESTERLY MID LEVEL FLOW FOR
TONIGHT. ADDITIONAL CIRRUS FROM THE NORTHWEST AND WEST MAY PASS
OVERHEAD WITH SOME LINGERING MID LEVEL CLOUDS ACROSS OUR SOUTHERN
COUNTIES.

A LIGHT WIND AND MAINLY THIN CIRRUS OVERHEAD SHOULD ALLOW
TEMPERATURES TO DROP INTO THE 50S AT MOST LOCATIONS. READINGS WILL
LIKELY FALL INTO THE 40S ACROSS OUR FAR NORTHERN COUNTIES.
-- End Changed Discussion --

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --
THE OVERALL SYNOPTIC SETUP IS COMPRISED OF A TROUGH IN EASTERN
CANADA THAT GRADUALLY LIFTS OUT OF THE NORTHEAST SATURDAY AND SUNDAY
WITH A NORTHWESTERLY FLOW ALOFT OCCURRING. THE UPPER-LEVEL FLOW
THEN UNDERGOES AMPLIFICATION SUNDAY AND DURING THE FIRST HALF OF
NEXT WEEK, AS A TROUGH EJECTS INTO THE PLAINS ALLOWING DOWNSTREAM
RIDGING TO TAKE PLACE FOR A TIME. THE RIDGE PLACEMENT HOWEVER ALLOWS
SURFACE HIGH PRESSURE CENTERED NEAR NORTHERN NEW ENGLAND OVER THE
WEEKEND TO SETTLE SOUTHWARD. THIS RESULTS IN AN ONSHORE FLOW
OCCURRING ACROSS OUR AREA, LEADING TO SOME COOLING AND ALSO
ADDITIONAL CLOUDS ESPECIALLY ON SUNDAY. THE PATTERN CONTINUES TO
EVOLVE THOUGH, AS THE RIDGE IS FORECAST TO TRANSLATE EAST AND WEAKEN
ALLOWING A WARM FRONT TO SLOWLY LIFT NORTHWARD LATE MONDAY INTO
WEDNESDAY. THIS NORTHWARD SHIFT OF THE WARM FRONT HOWEVER COULD BE
SLOWED THOUGH AS THE SURFACE LOW HANGS BACK ACROSS THE MIDWEST. OUR
CONFIDENCE IS ON THE LOWER SIDE REGARDING THE WARM FRONTAL
PRECIPITATION, BUT A GRADUAL INCREASE IN PRECIPITATION OVER THE
WEEKEND SHOULD OCCUR. THE UPPER-LEVEL TROUGH IN THE PLAINS THEN
TRACKS EASTWARD, DRIVING A SURFACE LOW AND COLD FRONT TOWARD OUR
AREA WEDNESDAY. THIS SYSTEM SHOULD ARRIVE IN OUR AREA LATER
WEDNESDAY AND THURSDAY. OVERALL, NEXT WEEK LOOKS UNSETTLED AT TIMES.
WE USED A MODEL BLEND APPROACH SATURDAY INTO MONDAY, THEN BLENDED A
DECENT AMOUNT OF NEW WPC GUIDANCE INTO CONTINUITY.

FOR SATURDAY AND SUNDAY...HIGH PRESSURE BUILDING ACROSS NEW ENGLAND
SATURDAY IS FORECAST TO SETTLE SOUTHWARD MORE SUNDAY. THIS IS IN
RESPONSE TO A TROUGH MOVING INTO THE PLAINS WHICH DRIVES A RIDGE
EASTWARD. THE TIMING AND POSITIONING OF THIS SURFACE HIGH WILL HAVE
AN IMPACT ON THE RETURN FLOW THAT EVENTUALLY WILL SETUP. A WAA
PATTERN SHOULD BE ONGOING NEAR THE OHIO VALLEY DURING THIS TIME
ALONG WITH AN INCREASING MOISTURE GRADIENT. THIS WILL EVENTUALLY
HELP TO TURN THE STALLED BOUNDARY INTO A WARM FRONT. THERE HAVE BEEN
SOME DIFFERENCES REGARDING THE PRECIPITATION ADVANCEMENT WITH THE
WARM FRONT. IT APPEARS THAT A MORE SOUTHERN POSITION OF THE WARM
FRONT MAY WIN OUT, WHICH DELAYS THE PRECIPITATION SOME. WE THEREFORE
SLOWED DOWN THE POPS, AND THE INCREASE THROUGH SUNDAY IS MORE NOTED
ACROSS OUR SOUTHERN ZONES CLOSER TO THE FRONTAL/ISENTROPIC LIFT.

IN ADDITION, AN ONSHORE FLOW IS FORECAST TO OCCUR, RESULTING IN
COOLER TEMPERATURES AND MORE CLOUDS. AS OF NOW, THE ONSHORE FLOW
DOES NOT LOOK REAL STRONG, BUT ENOUGH TO INCREASE THE CLOUDS
SATURDAY WITH LOWER CLOUDS OCCURRING SATURDAY NIGHT AND ESPECIALLY
SUNDAY. THIS COULD LEAD TO SOME EVENTUAL DRIZZLE AS DEW POINTS
INCREASE RESULTING IN A MOISTENING BOUNDARY LAYER. WE HAVE LOWER
CONFIDENCE REGARDING THIS, THEREFORE NO DRIZZLE OR FOG ADDED ATTM.
HIGH TEMPERATURES ARE COOLER SUNDAY DUE TO THE ONSHORE FLOW AND MORE
CLOUDS THAT ARE FORECAST. IF AN ABUNDANCE OF CLOUDS PREVAIL IN
COMBINATION WITH THE ONSHORE FLOW, TEMPERATURES WOULD BE EVEN COOLER
THAN CURRENTLY FORECAST.

FOR MONDAY THROUGH WEDNESDAY...OUR CONFIDENCE IN THE LARGE SCALE
FEATURES LOWERS SOME AS THERE ARE DECENT DIFFERENCES REGARDING THE
PLACEMENT OF THE WARM FRONT. THE NORTHEAST AND MID ATLANTIC
CONTINUES TO BE AN AREA WITH LESS CERTAINTY REGARDING THE FRONTAL
PROGRESSION AND ORIENTATION AS THE UPPER-LEVEL LOW TRAVERSES THE
MIDWEST AND GREAT LAKES REGION. THERE COULD BE A SECONDARY COOL
FRONT DROPPING DOWN FROM THE NORTH TUESDAY AS A SYSTEM LIFTS OUT OF
SOUTHEASTERN CANADA. IF THIS WERE THE CASE, IT WOULD SLOW THE
NORTHWARD PROGRESSION OF THE WARM FRONT ACROSS OUR AREA WITH THE
GREATEST WAA MORE TOWARD THE OHIO VALLEY. THE WARM FRONT SHOULD THEN
BE TOSSED NORTHWARD EITHER LATE TUESDAY OR WEDNESDAY AS LOW PRESSURE
SLIDES TOWARD THE UPPER OHIO VALLEY. GIVEN LOWER CONFIDENCE WITH THE
TIMING AND CONVECTIVE EVOLUTION TIED TO THE INCOMING FRONTAL
BOUNDARIES, WE FOLLOWED CLOSELY TO WPC GUIDANCE AND MAINTAINED CHC
POPS ACROSS THE AREA.

FOR THURSDAY...DESPITE LOWER CONFIDENCE WITH THE TIMING, OVERALL AN
UPPER-LEVEL TROUGH IS FORECAST TO AMPLIFY INTO THE NORTHEAST. THIS
DRIVES A COLD FRONT AND ASSOCIATED SURFACE LOW ACROSS OUR AREA. THIS
SHOULD RESULT IN SHOWERS, AS ANY THUNDER WOULD BE TIED TO IF ENOUGH
INSTABILITY CAN BE ATTAINED. IF THE FRONTAL BOUNDARY ARRIVES EARLY
ENOUGH, AT LEAST SOME SHOWERS COULD BE ONGOING TO START THE DAY. NO
SIGNIFICANT CHANGES WERE MADE TO THIS TIME FRAME.
-- End Changed Discussion --

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

VFR CONDITIONS ARE FORECAST THROUGH THE TAF PERIOD AS DRY AIR BUILDS
INTO OUR REGION FROM THE NORTHWEST AND NORTH. PATCHES OF CIRRUS WILL
LIKELY PASS OVERHEAD AND THERE MAY BE A FEW CUMULUS, MAINLY DURING
THE AFTERNOON AND EVENING.

A NORTH TO NORTHWEST WIND AROUND 6 TO 10 KNOTS IS ANTICIPATED INTO
THE MID AFTERNOON. THE NORTH TO NORTHWEST FLOW IS EXPECTED TO
WEAKEN, ALLOWING A SEA BREEZE FRONT TO WORK ITS WAY INLAND FROM THE
MID AFTERNOON HOURS INTO THE EARLY EVENING. IT SHOULD IMPACT KACY
AND KMIV LATE IN THE AFTERNOON AND IT MAY REACH KPHL AND KPNE IN THE
EVENING. A BREEZE OFF THE DELAWARE RIVER IS EXPECTED TO IMPACT KILG
DURING THE EVENING. THE WIND IS FORECAST TO BECOME LIGHT AND
VARIABLE AT ALL EIGHTS OF OUR TAF SITES FOR TONIGHT.

OUTLOOK...
SATURDAY...VFR WITH INCREASING CLOUDS DURING THE DAY, THEN PERHAPS
MVFR CEILINGS ARRIVING AT NIGHT. SOME SHOWERS ARE POSSIBLE IN THE
AFTERNOON AND AT NIGHT ESPECIALLY SOUTH OF KPHL. SOUTHEASTERLY WINDS
GENERALLY 5 TO 10 KNOTS.

SUNDAY...A DECENT CHANCE FOR SUB-VFR CEILINGS AS AN ONSHORE FLOW
STRENGTHENS SOME, AND SHOWERS SHOULD BE AROUND. EAST-SOUTHEAST WINDS
AROUND 10 KNOTS.

MONDAY THROUGH TUESDAY...MVFR CEILINGS AND/OR VISIBILITIES POSSIBLE
AT TIMES, ESPECIALLY WITH ANY SHOWERS OR THUNDERSTORMS. EAST TO
SOUTHEAST WINDS GENERALLY 5 TO 10 KNOTS MONDAY, POSSIBLY BECOMING
SOUTH-SOUTHWEST TUESDAY.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
HIGH PRESSURE FROM THE NORTHWEST AND NORTH IS FORECAST TO BUILD
ACROSS THE COASTAL WATERS OF NEW JERSEY AND DELAWARE FOR TODAY AND
TONIGHT. WIND SPEEDS AND WAVE HEIGHTS WILL REMAIN BELOW THE SMALL
CRAFT ADVISORY CRITERIA.

OUTLOOK...
A FRONTAL BOUNDARY STALLED TO OUR SOUTH TO START THE WEEKEND WILL
GRADUALLY WORK ITS WAY NORTHWARD AS A WARM FRONT. THIS FRONT HOWEVER
MAY NOT MOVE NORTH OF OUR AREA UNTIL LATE TUESDAY. AS HIGH PRESSURE
SETTLES ACROSS NEW ENGLAND SATURDAY THEN SHIFTS OFFSHORE SUNDAY AND
MONDAY, AN ONSHORE FLOW WILL RESULT ACROSS OUR AREA. THIS FLOW MAY
THEN TURN MORE SOUTHERLY TUESDAY, ALTHOUGH THIS WILL DEPEND ON THE
POSITIONING OF THE WARM FRONT. THE ONSHORE FLOW MAY INCREASE SOME
SATURDAY NIGHT AND SUNDAY AS THE PRESSURE GRADIENT TIGHTENS SOME,
ALTHOUGH IT APPEARS THE GFS MAY BE A BIT STRONG WITH THIS ATTM. AS A
RESULT, WE KEPT THE WINDS UNDER 25 KNOTS AND ALSO DID NOT GO AS HIGH
AS THE WAVEWATCH GUIDANCE. HOWEVER, THE PERIOD OF ONSHORE FLOW MAY
BE ENOUGH TO GET SEAS ON THE OCEAN TO AROUND 5 FEET LATER IN THE
WEEKEND INTO EARLY NEXT WEEK.
-- End Changed Discussion --

&&

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

&&

$$
SYNOPSIS...GORSE
NEAR TERM...IOVINO
SHORT TERM...IOVINO
LONG TERM...GORSE
AVIATION...GORSE/IOVINO
MARINE...GORSE/IOVINO