AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1103 PM EDT SUN APR 17 2011

.SYNOPSIS...
LOW PRESSURE MOVING ACROSS EASTERN CANADA SHOULD PULL COLD FRONT
FROM THE NORTHWEST INTO OUR REGION ON MONDAY NIGHT. THE BOUNDARY
IS EXPECTED TO MEANDER IN OUR VICINITY ON TUESDAY. LOW PRESSURE
MOVING ACROSS THE GREAT LAKES ON WEDNESDAY SHOULD PULL THE FRONT
TO OUR NORTH AT THAT TIME. A COLD FRONT FROM THE WEST IS EXPECTED
TO ARRIVE EARLY ON THURSDAY WITH HIGH PRESSURE FOLLOWING FOR
THURSDAY AND FRIDAY. ANOTHER AREA OF LOW PRESSURE IS FORECAST TO
PASS ACROSS THE GREAT LAKES ON FRIDAY NIGHT AND SATURDAY AND IT
SHOULD PULL A COLD FRONT THROUGH OUR REGION EARLY ON SUNDAY.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
A SHORT WAVE HAS BEEN MAKING ITS WAY THROUGH OUR AREA TONIGHT.
SHOWERS CONTINUE TO MOVE ACROSS THE NORTHERN AREAS IN ASSOCIATION
WITH THE SHORT WAVE. A RUMBLE OR TWO OF THUNDER ALSO REMAINS
POSSIBLE WITH ANY PASSING SHOWER. SHOWERS WILL TAPER OFF TONIGHT
AND SHOULD EXIT THE REGION BY AROUND MIDNIGHT. ANOTHER AREA OF
SHOWERS OFF TO OUR WEST ACROSS THE PENNSYLVANIA/MARYLAND BORDER
HAS BEEN SLOWLY MAKING EASTWARD PROGRESS. HOWEVER, THE DRY AIR
ACROSS OUT AREA HAS HELPED TO ERODE THESE SHOWERS AS THE MOVE
EASTWARD.

THE SOUTHWEST WIND WILL REMAIN A BIT GUSTY UNTIL THE SHORT WAVE
PASSES AND THEN IS EXPECTED TO DIMINISH. THE SKY COVER WILL LIKELY
VARY FROM PARTLY CLOUDY TO MOSTLY CLEAR. WITH THE DRY AIR MASS,
TEMPERATURES SHOULD DROP INTO THE 30S IN THE ELEVATED TERRAIN AND
INTO THE 40S ELSEWHERE.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
THE MID AND UPPER LEVEL PATTERN SHOULD BE SOMEWHAT ZONAL FOR
MONDAY. A TROUGH IS THEN FORECAST TO DIG OVER THE ROCKY MOUNTAIN
STATES ON TUESDAY BEFORE LIFTING TO THE GREAT LAKES ON WEDNESDAY.

FOR MONDAY, WE ARE ANTICIPATING AN INCREASE IN HIGH LEVEL CLOUDS.
TEMPERATURES SHOULD BE NEAR NORMAL IN OUR NORTHERN COUNTIES AND A
BIT ABOVE NORMAL IN THE SOUTH.

A FRONTAL BOUNDARY FROM THE NORTHWEST WILL LIKELY APPROACH LATE
ON MONDAY AND IT SHOULD SETTLE IN OUR REGION ON MONDAY NIGHT.
THERE IS A CHANCE OF RAIN AT THAT TIME, MAINLY ACROSS OUR NORTHERN
COUNTIES.

THE BOUNDARY WILL SINK FARTHER SOUTH IN OUR REGION ON TUESDAY. A
CHILLY OVERCAST DAY IS IN STORE FOR MOST OF OUR FORECAST AREA
WHICH SHOULD LIE TO THE NORTH OF THE FRONT. DEPENDING ON WHERE THE
FRONT STALLS, OUR FAR SOUTHERN COUNTIES MAY NOT BE AFFECTED AND
THEY COULD RISE TO AROUND 70 DEGREES AT THAT TIME. OF COURSE,
FORECASTING THE EVENTUAL LOCATION OF THIS TYPE OF FRONT AT THIS
TIME OF THE YEAR IS QUITE TRICKY AND OUR FAR SOUTHERN COUNTIES
COULD END UP IN THE COOL AND CLOUDY CONDITIONS, AS WELL. WE WILL
CONTINUE TO INDICATE A CHANCE FOR RAIN ON TUESDAY WITH HIGHER POPS
IN THE NORTH THAN IN THE SOUTH.

THE FRONT IS ANTICIPATED TO LIFT TO OUR NORTH ON WEDNESDAY AS LOW
PRESSURE MOVES ACROSS THE GREAT LAKES. TEMPERATURES MAY RISE NEAR
80 IN SOME OF OUR SOUTHERN AND CENTRAL COUNTIES. WITH A COLD FRONT
APPROACHING FROM THE WEST, WE ARE ANTICIPATING SHOWERS. AS THE AIR
MASS DESTABILIZES, THUNDERSTORMS ARE POSSIBLE ON WEDNESDAY
AFTERNOON, ESPECIALLY IN EASTERN PENNSYLVANIA AND ON THE DELMARVA.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
THIS TIME FRAME APPEARS TO BE UNSETTLED AT TIMES. AS THE RIDGING
NEAR THE WEST COAST BREAKS DOWN EARLY ON, 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 ENSEMBLE MEAN. WE INITIALIZED THE DATABASE WITH
HPC GUIDANCE THAN MADE SOME TWEAKS BASED ON ADDITIONAL
COLLABORATION.

BASED ON THE ABOVE, A WARM FRONT SHOULD HAVE CLEARED THE AREA AT
THE START OF THIS TIME FRAME AS LOW PRESSURE TRACKS ACROSS
SOUTHEASTERN CANADA. THIS WILL SWEEP A COLD FRONT THROUGH OUR AREA
WEDNESDAY NIGHT INTO EARLY THURSDAY MORNING. GIVEN THE WARM
AIRMASS AHEAD OF THIS BOUNDARY ALONG WITH THE MOISTURE RETURN, WE
WILL CONTINUE TO INCLUDE A CHC OF THUNDER WEDNESDAY EVENING BEFORE
TAPERING POPS DOWN FROM WEST TO EAST FROM ABOUT 04Z ONWARD.

AS A STRONG SURFACE HIGH THEN SLIDES ACROSS THE GREAT LAKES TO
THE NORTHEAST, IT SHOULD TEND TO BUILD DOWN INTO THE MID ATLANTIC
STATES ALLOWING THE AFOREMENTIONED COLD FRONT TO BE PUSHED WELL TO
OUR SOUTH AND POSSIBLY DISSIPATE. A COOLER AIRMASS WILL ACCOMPANY
THIS SURFACE HIGH AND ULTIMATELY WE MAY HAVE A LIGHT ONSHORE FLOW
OCCURRING LATER 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 AND POSSIBLY A PERIOD OF
OVERRUNNING RAIN. WE STARTED TO INCREASE THE POPS LATER FRIDAY AND
CONTINUED THAT SATURDAY INTO SUNDAY. THE COLD FRONT ATTM IS
SCHEDULED TO BE MOVING THROUGH OUR AREA EARLY SUNDAY. THERE IS
HOWEVER SOME UNCERTAINTY ON THE TIMING ESPECIALLY WITH THE MOSTLY
ZONAL FLOW REGIME, THEREFORE KEPT POPS IN THE LOWER CHC RANGE. DID
TRY TO PORTRAY THE WARM FRONTAL OVERRUNNING POTENTIAL FROM SOUTH
TO NORTH SWITCHING FROM RAIN TO SHOWERS. THERE LOOKS TO BE ENOUGH
OF A WARM SECTOR ACROSS ESPECIALLY OUR DELMARVA ZONES FOR THUNDER,
THEREFORE ADDED A CHC IN FOR SATURDAY AFTERNOON AND EARLY EVENING.
AS FOR TEMPERATURES, WE GENERALLY FOLLOWED HPC WITH MAINLY MINOR
TWEAKS.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

A STRONG AREA OF LOW PRESSURE ACROSS SOUTHEASTERN CANADA IS
WEAKENING. MEANWHILE, WEAK HIGH PRESSURE IS TO OUR SOUTH. THE
PRESSURE GRADIENT BETWEEN THESE TWO SYSTEMS IS TIGHTENED, HOWEVER
THIS WILL LOOSEN THROUGH THE NIGHT. THIS ALONG WITH THE SURFACE
TEMPERATURES COOLING WILL ALLOW VERTICAL MIXING TO WANE. THEREFORE,
THE GUSTY WINDS WILL SUBSIDE THROUGH THE REMAINDER OF THE EVENING
AND THIS HAS ALREADY STARTED AT SOME TERMINALS. BASED ON THE TRACK
OF THE LOW PRESSURE SYSTEM AND A DISTURBANCE TRACKING ALONG ITS
SOUTH SIDE, THE SURFACE FLOW HAS SHIFTED TO THE SOUTHWEST. THIS WILL
CONTINUE FOR AWHILE THIS EVENING BUT THEN SHIFT TO WEST AND
NORTHWEST TONIGHT AS THE SYSTEM MOVES FARTHER AWAY. THERE HAS BEEN
SOME INSTABILITY SHOWERS MOVING ACROSS PENNSYLVANIA AND NORTHERN NEW
JERSEY, HOWEVER THE DRY LOW LEVELS IS KEEPING MOST OF THIS RATHER
LIGHT OR NOT EVEN REACHING THE GROUND. THIS ACTIVITY IS EXPECTED TO
DISSIPATE AS DAYTIME HEATING IS LOST, THEREFORE NO MENTION IS
CARRIED AT THIS TIME. VFR CONDITIONS ARE EXPECTED TO PERSIST AS BANDS
OF MAINLY ALTOCUMULUS MOVE THROUGH PARTS OF THE AREA BEFORE THINNING
OUT. SOME HIGH LEVEL CLOUDS MAY THEN MOVE THROUGH IN THE FAST
WESTERLY UPPER-LEVEL FLOW.

FOR MONDAY, HIGH PRESSURE IS POSITIONED TO OUR SOUTHEAST WITH A
SOUTHWESTERLY WIND ACROSS THE AREA. THERE APPEARS TO BE ENOUGH OF A
GRADIENT AND MIXING TO ALLOW GUSTS TO NEAR 20 KNOTS DURING THE
AFTERNOON BEFORE WANING. A FRONTAL BOUNDARY WILL BEGIN TO MOVE
INTO OUR AREA. AN AREA OF RAIN NORTH OF THIS FRONT LOOKS TO REMAIN
NORTH OF OUR TERMINALS ALTHOUGH A TOUCH OF RAIN CANNOT BE RULED OUT
FROM ABOUT KRDG TO KTTN ON NORTHWARD IN THE AFTERNOON AND EVENING.
FOR NOW, JUST INCREASED THE CLOUDS WITH MAINLY MID LEVEL BASES
ARRIVING.

OUTLOOK...
MONDAY NIGHT AND TUESDAY...A FRONTAL BOUNDARY WILL REMAIN NEARBY
WITH ENERGY TRACKING ALONG IT. THIS WILL ALLOW THE CLOUDS TO
INCREASE AND LOWER ESPECIALLY DURING TUESDAY. MVFR TO EVEN IFR IS
POSSIBLE BY THE END OF TUESDAY. A PERIOD OF RAIN MAY MOVE ACROSS THE
AREA ESPECIALLY TUESDAY PARTICULARLY FROM ABOUT KPHL ON NORTHWARD.

WEDNESDAY AND THURSDAY...LOW PRESSURE TRACKS ACROSS THE GREAT LAKES
AND SOUTHEASTERN CANADA. ANY RAIN SHOULD LIFT NORTH OF THE AREA
WEDNESDAY MORNING WITH A WARM FRONT THEN POTENTIALLY A GUSTY
SOUTHWEST WIND DEVELOPS SOUTH OF THE FRONT. THE LOW-LEVEL MOISTURE
INCREASES BUT ENOUGH MIXING SHOULD ALLOW FOR VFR CONDITIONS ONCE THE
WARM FRONT PASSES. SOME SHOWERS AND THUNDERSTORMS MAY THEN PRECEDE
AND ACCOMPANY THE COLD FRONT WEDNESDAY AFTERNOON AND NIGHT. THE COLD
FRONT SHOULD BE EAST OF THE AREA BY 12Z THURSDAY WITH A WIND SHIFT
TO THE WEST AND NORTHWEST. THESE WINDS MAY BE GUSTY THURSDAY.

FRIDAY...VFR AS HIGH PRESSURE SETTLES OVER THE AREA. LIGHT WINDS BUT
PERHAPS A SEA/BAY BREEZE AT KACY AND KILG.

&&

.MARINE...
A SOUTHWEST FLOW ON THE SOUTH SIDE OF A LARGE UPPER-LEVEL TROUGH AND
SURFACE LOW WILL PERSIST TONIGHT. THE WINDS ALOFT ARE STRONG,
HOWEVER THE MILDER BOUNDARY LAYER HAS PREVENTED BETTER MIXING FROM
OCCURRING OVER THE WATERS. AS THE BOUNDARY LAYER COOLS TONIGHT
THOUGH, MIXING MAY IMPROVE TO KEEP THE WINDS UP BUT IT APPEARS
ENOUGH OF A STABLE LAYER OCCURS TO KEEP WINDS BELOW ADVISORY
CRITERIA OVER DELAWARE BAY /NEAR 25 KNOTS OVER THE COASTAL WATERS/.
THEREFORE, IT WAS DECIDED TO CANCEL THE ADVISORY FOR DELAWARE BAY.
THE SEAS REMAIN ELEVATED ON THE OCEAN BUT HAVE BEEN TRENDING LOWER
THE LAST FEW HOURS. IF THESE HOLD UP LONGER, THE SMALL CRAFT
ADVISORY MAY NEED TO BE EXTENDED BEYOND 10Z MONDAY.

THE LATEST WAVEWATCH GUIDANCE INDICATES THAT THIS WILL BE A BUSY
WEEK FOR MARINE HEADLINES. ADDITIONAL HEADLINES MAY BE NEEDED MONDAY
NIGHT WITH THE FIRST LOW AND A BETTER SHOT AROUND MIDWEEK WITH THE
WARM FRONT.

&&

.HYDROLOGY...
THERE IS NO LONGER ANY FLOODING IN EASTERN PENNSYLVANIA OR ON THE
UPPER DELMARVA. MOST OF SOUTHERN NEW JERSEY IS ALSO NOT
EXPERIENCING ANY FLOODING. THE ONLY EXCEPTION IS THE NORTH BRANCH
OF THE RANCOCAS CREEK WHICH MAY HAVE SOME MINOR FLOODING INTO
TUESDAY.

OUR MAIN CONCERN REMAINS IN THE RARITAN AND PASSAIC RIVER BASINS
IN NEW JERSEY. A NUMBER OF FLOOD WARNINGS ARE IN EFFECT.

&&

.TIDES/COASTAL FLOODING...
CONDITIONS CONTINUE TO IMPROVE WRT COASTAL FLOODING, HOWEVER WE
MAY NOT BE COMPLETELY OUT OF THE WOODS YET. THE EVENING/EARLY
MONDAY MORNING TIDES ARE THE HIGHER ONES AND WITH THE FULL MOON,
ASTRONOMICAL TIDES ARE ALREADY RUNNING VERY HIGH. IN MANY
LOCATIONS, SUCH AS ON THE TIDAL DELAWARE RIVER AND NEW CASTLE AND
SALEM COUNTIES, IT WON`T TAKE MUCH (0.25 TO 0.5) TO REACH MINOR
TIDAL FLOODING CONDITIONS. THE GOOD NEWS IS THAT EVEN THOUGH THE
ASTRONOMICAL TIDES ARE HIGHER, THE DEPARTURES ARE SMALLER. ON THE
OCEAN FRONT, MOST LOCATIONS LOOK TO BE VERY CLOSE, BUT JUST FALL
SHORT. OF COURSE, THE SITUATION WILL CONTINUE TO BE MONITORED AND
ANY ADVISORIES ISSUED AS NEEDED.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT MONDAY FOR ANZ450>455.

&&

$$
SYNOPSIS...IOVINO