Coastal Flood Advisory 11, NWS Philadelphia/Mount Holly

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
452 AM EDT SUN APR 17 2011

.SYNOPSIS...
A WEAK AREA OF HIGH PRESSURE WILL BUILD INTO THE REGION TODAY.
A COLD FRONT WILL THEN MOVE INTO OUR REGION ON MONDAY NIGHT AND
THEN STALL NEARBY ON TUESDAY. THE STALLED FRONT WILL THEN MOVE
NORTHWARD AS A WARM FRONT LATE TUESDAY INTO WEDNESDAY. ANOTHER
LOW IS FORECAST TO MOVE ACROSS THE SOUTHEASTERN CANADA ON
WEDNESDAY NIGHT INTO THURSDAY PULLING YET ANOTHER COLD FRONT
THROUGH OUR REGION. HIGH PRESSURE WILL THEN RETURN FOR THURSDAY
AND FRIDAY. ANOTHER SYSTEM MAY AFFECT THE REGION AROUND THE END
OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE HEAVY RAIN AND THUNDERSTORMS HAVE MOVED OUT OF THE AREA AND WE
HAVE CANCELLED THE FLOOD WATCH, AS NO ADDITIONAL FLOODING IS
EXPECTED. HOWEVER, THERE ARE STILL SEVERAL STATEMENTS AND FLOOD
WARNINGS IN EFFECT. PLEASE CHECK OUR WEBSITE FOR UPDATES AND THE
LATEST FORECASTS ON THE AREA CREEKS, RIVERS AND STREAMS.

THE SURFACE LOW HAS PASSED TO OUR NORTH AND THE COLD FRONT HAS
MOVED OFFSHORE. PRECIPITATION HAS MOSTLY ENDED WITH ONLY SOME
SHOWERS MOVING THROUGH THE AREA. MOST AREAS SHOULD DRY OUT TODAY
ALTHOUGH WE MAY SEE A FEW MORE SHOWERS MOVE THROUGH THIS AFTERNOON
AS A SHORTWAVE CROSS THE AREA. SKIES WILL BECOME LESS CLOUDY
TODAY, ESPECIALLY ACROSS THE SOUTHERN AREAS AND THIS SHOULD ALLOW
FOR TEMPERATURES TO RISE INTO THE 60S, WITH 50S ACROSS THE HIGHER
ELEVATIONS.

WINDS HAVE COME AROUND TO THE WEST AND HAVE BEEN FAIRLY LIGHT
OVERNIGHT. GUIDANCE INDICATES A GOOD PUSH OF COLD AIR ALOFT ACROSS
THE REGION AND WINDS SHOULD MIX DOWN TO THE SURFACE A BIT WITH
GUSTS IN THE 30-35 MPH RANGE. TOSSED AROUND THE IDEA FOR A WIND
ADVISORY FOR TODAY BUT IT DOESN'T LOOK LIKE THE GUSTY WINDS ALOFT
WILL REALLY GET A CHANCE TO MIX DOWN EFFICIENTLY. HOWEVER, A FEW
GUSTS AROUND 40 MPH CAN NOT BE RULED OUT COMPLETELY, ESPECIALLY
ACROSS THE HIGHER TERRAIN FOR TODAY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
TONIGHT, ANY LIGHT SHOWERS SHOULD DISSIPATE AS THE SHORTWAVE
MOVES OFF TO THE EAST DURING THE EVENING. BEHIND THE EXITING
SHORTWAVE,THE UPPER LEVEL PATTERN BECOMES QUITE ZONAL AND REMAINS
AS SUCH THROUGH TUESDAY.

AT THE SURFACE, A WEAK RIDGE OF HIGH PRESSURE WILL QUICKLY MOVE
ACROSS THE AREA LATE SUNDAY AS A COLD FRONT DROPS DOWN FROM THE
NORTHWEST. WITH THE ZONAL FLOW IN PLACE THERE REALLY IS NOTHING TO
MAKE THE FRONT MOVE OFF TO THE SOUTHEAST AND IT ESSENTIALLY
BECOMES A STATIONARY FRONT ACROSS OUR AREA. WAVES OF LOW PRESSURE
LOOK TO RIDE ALONG THE STALLED BOUNDARY BRINGING US UNSETTLED
WEATHER FOR TUESDAY. WE HAVE INCLUDED CHC/SCHC POPS FOR MONDAY
NIGHT WITH THE ARRIVAL OF THE FRONT AND THEN CONTINUED THEM INTO
TUESDAY AS THE BOUNDARY REMAINS ACROSS OUR AREA. WE HAVE ADDED
SOME THUNDER TO TUESDAY AFTERNOON AS SOME CONVECTION MAY FORM AS
THE FRONT STARTS TO PUSH ITS WAY NORTHWARD. THERE ARE STILL SOME
TIMING AND PLACEMENT CONCERNS WITH THIS FEATURE AND AS A RESULT,
WE HAVE, LOWER THAN AVERAGE CONFIDENCE AT THIS TIME.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
THIS TIME FRAME APPEARS TO BE UNSETTLED BUT WILL ALSO FEATURE A
WARM UP AROUND WEDNESDAY. AS THE RIDGING NEAR THE WEST COAST
BREAKS DOWN, THE FLOW IS FORECAST TO BECOME GENERALLY ZONAL ACROSS
THE U.S. THIS MAY THEN TRY TO AMPLIFY SOME TOWARD THE END OF THE
PERIOD AS TROUGHING MAY DIG ACROSS THE WEST AND ALSO THE MIDWEST.
HPC UTILIZED AN EVEN BLEND OF THE GFS/ECMWF THROUGH THURSDAY, THEN
BLENDED IN AN INCREASING PERCENTAGE OF THE ECMWF ENSEMBLE MEAN.
THIS IS TO PARTIALLY CORRECT FOR THE GENERAL FAST BIAS OF THE GFS
AND ITS ENSEMBLE MEMBERS. WE INITIALIZED THE DATABASE WITH HPC
GUIDANCE THAN MADE SOME TWEAKS BASED ON ADDITIONAL COLLABORATION.

BASED ON THE ABOVE, A WARM FRONT IS FORECAST TO BE SITTING MOSTLY
ACROSS OUR SOUTHERN ZONES TUESDAY NIGHT WHICH THEN LIFTS NORTHWARD
WEDNESDAY. THIS WILL PLACE MOST OF THE CWA IN THE WARM SECTOR WITH
A RATHER WARM SOUTHWEST FLOW OCCURRING FOR A TIME WEDNESDAY. THERE
IS SOME UNCERTAINTY WITH THE DEGREE OF SHOWERS OR A PERIOD OF RAIN
BECOMING STRETCHED WEST TO EAST NORTH OF THE WARM FRONT. FOR NOW,
WE KEPT POPS IN THE CHC TO SLIGHT CHC RANGE WITH THE HIGHEST
VALUES ACROSS THE FAR NORTH TUESDAY NIGHT INTO WEDNESDAY, WITH THE
POPS THEN ERODING FROM SOUTH TO NORTH WEDNESDAY MORNING. THIS
PRECIPITATION MAY BE TIED TO ANY CONVECTIVE ACTIVITY WELL TO OUR
WEST AS IT ROLES EASTWARD, SO FOR NOW WE WILL GO WITH SHOWERS
INSTEAD OF RAIN. IN THE WARM SECTOR WEDNESDAY, STRONG WAA IS
FORECAST TO BOOST 850 MB TEMPERATURES TO NEAR +18C. THIS ALONG
WITH AT LEAST SOME SUNSHINE AND INCREASED MIXING SHOULD ALLOW
HIGHS TO NEAR 80 DEGREES SOUTH OF THE WARM FRONT ESPECIALLY FROM
THE I-95 CORRIDOR ON EASTWARD /COOLER ALONG THE COAST THOUGH AS
THE SURFACE WINDS MAY BE TO SOUTHERLY FOR AWHILE/.

AS LOW PRESSURE TRACKS ACROSS SOUTHEASTERN CANADA WEDNESDAY NIGHT
INTO THURSDAY, ITS COLD FRONT SWEEPS THROUGH OUR AREA. GIVEN THE
WARM AIRMASS AHEAD OF THIS BOUNDARY ALONG WITH THE MOISTURE
RETURN, WE WILL CONTINUE TO INCLUDE A CHC OF THUNDER WEDNESDAY
AFTERNOON AND EVENING. AS A STRONG SURFACE HIGH THEN SLIDES ACROSS
SOUTHERN CANADA, IT SHOULD TEND TO BUILD DOWN INTO THE MID
ATLANTIC STATES ALLOWING THE AFOREMENTIONED COLD FRONT TO BE
PUSHED WELL TO OUR SOUTH. A COOLER AIRMASS WILL ACCOMPANY THIS
SURFACE HIGH AND ULTIMATELY WE MAY HAVE A LIGHT ONSHORE FLOW
OCCURRING LATE THURSDAY AND FRIDAY. AS THE SURFACE HIGH SLIDES OFF
THE NEW ENGLAND COAST FRIDAY NIGHT AND SATURDAY, LOW PRESSURE
SHOULD BE QUICKLY MOVING ACROSS THE GREAT LAKES REGION. ITS
ASSOCIATED WARM FRONT WILL BE MAKING ITS WAY INTO OUR AREA
SATURDAY WITH THE CHC OF SHOWERS /OVERRUNNING RAIN?/. WE STARTED
TO INCREASE THE POPS FRIDAY AND CONTINUED THAT SATURDAY. THERE
HOWEVER IS SOME UNCERTAINTY ON THE TIMING ESPECIALLY WITH THE
MOSTLY ZONAL FLOW REGIME, THEREFORE KEPT POPS IN THE LOW CHC
RANGE. AS FOR TEMPERATURES, WE GENERALLY FOLLOWED HPC WITH MAINLY
MINOR TWEAKS.

&&

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

THE CIGS/VSBYS HAVE IMPROVED RAPIDLY BEHIND THE COLD FRONT WHICH
CROSSED THE AREA SAT NIGHT. FLYING CONDITIONS ARE BEGINNING MOSTLY
VFR NOW...THE WINDS HAVE YET TO INCREASE AS EARLIER EXPECTED. I WILL
INDICATE THE WINDS INCREASING AFTER DAWN WITH GUSTS OVER 20 KNOTS
FOR THE BALANCE OF THE DAY. SKIES WHICH ARE MOSTLY CLOUDY AS OF 06Z
WILL BECOME MAINLY CLR BY DAWN IN MOST AREAS. THERE WILL BE SOME
MORE CLOUDINESS THIS AFTERNOON...WHICH WILL BE REFLECTED IN THE 12Z
TAFS. SKIES WILL BECOME MOSTLY CLR TONIGHT.

HIGH PRESSURE WILL PASS TO THE EAST MON AND THE NEXT WEATHER SYSTEM
WILL APPROACH FROM THE WEST. A WARM FRONT AHEAD OF THE SYSTEM WILL
BRING INCREASING CLOUDS MON WHICH WILL REMAIN INTO TUE. SHOWERS MAY
OCCUR MON EVENING AND TUE. MOSTLY VFR CONDITIONS EXPECTED UNTIL TUE
MORNING WHEN SOME MVFR CIGS MAY ARRIVE.

&&

.MARINE...
GALES HAVE DIMINISHED ON THE WATERS AND THE GALE FLAG WILL COME DOWN
ON THE OCEAN WITH THE 400 AM CWF ISSUANCE. WINDS WILL STILL BE GUSTY
TODAY...SO A SCA FLAG WILL BE ISSUED FOR THE WATERS TODAY. IT WILL
CONTINUE ON DEL BAY UNTIL THIS EVENING (WHEN THE GUSTS SUBSIDE) AND
UNTIL EARLY MORNING MON (WHEN THE SEAS SUBSIDE).

HIGH PRESSURE WILL GRADUALLY BUILD IN TODAY THROUGH MONDAY AND THEN
PASS EAST. THE NEXT SYSTEM MAY BRING MORE SCA CONDITIONS MON NIGHT
AND TUE AS A WARM FRONT BEGINS TO APPROACH FROM THE SOUTH.

&&

.TIDES/COASTAL FLOODING...
TIDAL FLOODING HAS ENDED ALONG THE DELAWARE RIVER. THE GAGE AT
PHILADELPHIA HAS FALLEN BACK BELOW FLOOD STAGE. THE COASTAL FLOOD
WARNING HAS BEEN CANCELED.

THE COASTAL FLOOD WARNING FOR THE CHESAPEAKE WILL CONTINUE
THROUGH THE PRESENT HIGH TIDE CYCLE. MODERATE TIDAL IS BEING
OBSERVED AT CAMBRIDGE, MD AND WILL CONTINUE THROUGH THE MORNING.
THE NEXT HIGH TIDE IS NOT EXPECTED TO PRODUCE TIDAL FLOODING.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...COASTAL FLOOD WARNING UNTIL 10 AM EDT THIS MORNING FOR MDZ008-
     012-015-019-020.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 AM EDT MONDAY FOR ANZ450>455.
     SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ430-
     431.

&&

SYNOPSIS...MEOLA
NEAR TERM...MEOLA
SHORT TERM...MEOLA
LONG TERM...GORSE
AVIATION...O'HARA
MARINE...O'HARA
TIDES/COASTAL FLOODING...O'HARA

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