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000
FXUS61 KPHI 180742
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
342 AM EDT SAT MAY 18 2013

.SYNOPSIS...
A FRONTAL BOUNDARY EXTENDED FROM THE NORTH CENTRAL STATES, ACROSS
THE OHIO RIVER VALLEY TO THE WATERS OFF NORTH CAROLINA EARLY THIS
MORNING. THE BOUNDARY IS EXPECTED TO WEAKEN AND DISSIPATE AS IT
MEANDERS OVER THE SAME GENERAL AREA THROUGH MONDAY. MEANWHILE,
HIGH PRESSURE SHOULD REMAIN TO OUR NORTHEAST AND EAST. ANOTHER
FRONTAL BOUNDARY FROM THE NORTH IS FORECAST TO DROP INTO OUR
REGION ON TUESDAY NIGHT AND WEDNESDAY. THE FRONT MAY BEGIN TO LIFT
BACK TO THE NORTH LATE IN THE WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A 06Z SURFACE ANALYSIS PLACED HIGH PRESSURE ACROSS THE NORTHEAST
INTO SOUTHEASTERN CANADA. A STATIONARY FRONT WAS DRAPED FROM THE
NORTHERN PLAINS TO THE UPPER OHIO VALLEY, THEN DOWN ACROSS
VIRGINIA AND EASTERN NORTH CAROLINA. AN UPPER AIR ANALYSIS SHOWED
A TROUGH IN THE WEST AND A RIDGE FROM THE MIDWEST INTO THE GREAT
LAKES. A TROUGH WAS IN NORTHERN NEW ENGLAND. THERE WERE SEVERAL
AREAS OF FOCUSED 850 MB WAA FROM THE MIDWEST DOWN THROUGH THE
PLAINS.

OUR SENSIBLE WEATHER IS ANTICIPATED TO BE IN A TRANSITIONING
STATE TODAY. THIS IS COURTESY OF A MID LEVEL LOW THAT IS GENERALLY
WEAKENING AS IT SLIDES EASTWARD FROM THE OHIO VALLEY. GIVEN THE
NORTHWESTERLY FLOW ALOFT HOWEVER, THIS FEATURE IS ANTICIPATED TO
BE GENERALLY DIRECTED TOWARD OUR SOUTH TODAY. THIS FEATURE IS
EMBEDDED IN A BUILDING MID LEVEL RIDGE FROM THE LOWER MISSISSIPPI
VALLEY AND INTO THE GREAT LAKES. THE MAIN FORECAST CHALLENGE FOR
TODAY /AND EVEN THROUGH TONIGHT/ IS THE TIMING AND AREAL COVERAGE
OF SHOWERS ARRIVING FROM THE SOUTHWEST. HIGH PRESSURE OVER
SOUTHEASTERN CANADA IS FORECAST TO BUILD SOUTH-SOUTHEAST, AND THIS
MAY HELP HOLD THE NORTHEASTWARD ADVANCEMENT OF THE SHOWERS.

THE MID LEVEL LOW IS PRODUCING SOME LOW-LEVEL WAA ALONG WITH SOME
THETA-E ADVECTION. THIS IS THE MOST PRONOUNCED ACROSS THE DELMARVA
AND THEN EVENTUALLY ACROSS SOUTHERN NEW JERSEY. THIS WILL RESULT
IN ISENTROPIC LIFT, HOWEVER THIS IS GENERALLY ON THE WEAKER SIDE.
THE OVERALL LIFT FARTHER NORTH IS EVEN WEAKER, HOWEVER THERE IS A
THERMAL GRADIENT FORECAST TO BE IN PLACE ALONG WITH A THETA-E
GRADIENT. AT THE SURFACE, A SOUTHEASTERLY FLOW IS EXPECTED WHICH
WILL GRADUALLY HELP TO INCREASE THE LOW-LEVEL MOISTURE. ALL OF
THIS IS FORECAST TO BE ON THE WEAKER SIDE, THEREFORE MOSTLY AN
INCREASE IN CLOUDS IS ANTICIPATED THROUGH THE DAY WITH SOME
SHOWERS MAINLY ACROSS THE DELMARVA. SOME ONGOING CONVECTION ACROSS
VIRGINIA EARLY THIS MORNING APPEARS TO BE FOCUSED NEAR THE STALLED
FRONT AND WITHIN AN AREA OF DEEPER MOISTURE. THIS ACTIVITY APPEARS
TO STAY JUST SOUTH OF DELAWARE EARLY THIS MORNING. THE FORECAST
SOUNDINGS ALSO INDICATE THE MOISTENING IS GRADUAL, THEREFORE WE
ARE NOT ANTICIPATING LOW CLOUDS DEVELOPING DESPITE THE
SOUTHEASTERLY FLOW. THE AIR MASS ACROSS OUR CWA TODAY LOOKS STABLE
ENOUGH, THEREFORE WE CONTINUED TO NOT INCLUDE A THUNDER MENTION.

AS FOR HIGH TEMPERATURES, THE AMOUNT OF CLOUD COVER ALONG WITH A
SOUTHEASTERLY FLOW WILL HELP TO KEEP THEM COOLER THAN YESTERDAY
FOR MANY AREAS. THIS WILL ALSO RESULT IN COOL CONDITIONS CLOSER TO
THE COAST. WE USED AN EVEN BLEND OF THE GFS/NAM MOS WITH SOME
MAINLY MINOR ADJUSTMENTS. THE WARMEST TEMPERATURES ARE MAINLY
ACROSS THE NORTHERN ZONES WHERE MORE FILTERED SUNSHINE MAY HOLD
THE LONGEST.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
THE WEAK MID LEVEL LOW WILL CONTINUE TO TRACK EASTWARD INTO THE
DELMARVA. MEANWHILE, THE CENTER OF HIGH PRESSURE IS FORECAST TO
SLIDE SOUTHWARD OFF THE NEW ENGLAND COAST. THIS WILL RESULT IN A
CONTINUATION OF A SOUTHEASTERLY FLOW AT THE SURFACE, WHICH VEERS
TO MORE SOUTHERLY AT 850 MB. AS THIS OCCURS, THE LOW-LEVEL WAA IS
MAINTAINED WITH EVEN SOME INCREASE IN THE WINDS ACROSS THE
SOUTHERN ZONES TOWARD MORNING. THIS ALONG WITH CONTINUED THETA-E
ADVECTION IS EXPECTED TO RESULT IN ENOUGH ISENTROPIC LIFT TO
PRODUCE AN EXPANDING AREA OF SHOWERS FROM NORTH TO SOUTH. THE
AREAL COVERAGE OF THE SHOWERS IS SOMEWHAT IN QUESTION THOUGH,
THEREFORE WE OPTED TO HOLD THE POPS UNDER LIKELY. IT MAY TAKE ALL
NIGHT FOR ANY SHOWERS TO REACH THE FAR NORTHERN ZONES AS SOME
DRIER AIR MAY HOLD ON WITH THE MAIN THETA-E ADVECTION AND WAA
FOCUSED FARTHER SOUTH. THEREFORE, WE SLOWED THE INCREASE IN THE
POPS SOME FROM SOUTH TO NORTH. THE AIR MASS ACROSS OUR CWA LOOKS
STABLE ENOUGH, THEREFORE WE CONTINUED TO NOT INCLUDE A THUNDER
MENTION.

THE COMBINATION OF LOW-LEVEL WAA AND MOISTURE ADVECTION WILL
RESULT IN A RATHER CLOUDY NIGHT. THE CLOUDS ARE EXPECTED TO LOWER
THROUGH THE NIGHT AS THE BOUNDARY LAYER MOISTENS UP. THE FORECAST
SOUNDINGS GENERALLY SHOW THIS PROCESS NOT BEING RUSHED, THEREFORE
WE DID NOT INCLUDE DRIZZLE. THIS IS ALSO SUPPORTED BY JUST ENOUGH
DRY AIR IN THE BOUNDARY LAYER REMAINING A BIT LONGER. AN ONSHORE
FLOW CAN BE TRICKY SOMETIMES, THEREFORE WE WILL SEE HOW QUICK THE
MOISTURE MOVES IN AND DEEPENS. THIS SHOULD ALSO LIMIT ANY FOG
OVERNIGHT, ESPECIALLY AS THE DEW POINTS ARE NOT FORECAST TO
RAPIDLY INCREASE.

AS FOR LOW TEMPERATURES, WE WENT WITH AN EVEN GFS/NAM MOS BLEND.
THE TEMPERATURES ONCE THEY FALL BACK DURING THE EVENING MAY TEND
TO HOLD NEARLY STEADY AS CLOUDS LOWER.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
THE MID LEVEL PATTERN IS EXPECTED TO FEATURE THE POLAR VORTEX
WELL TO OUR NORTHEAST WITH A TROUGH SETTLING OVER THE WESTERN HALF
OF THE COUNTRY ON SUNDAY. THERE SHOULD BE A RIDGE OVER THE EAST
WITH ITS AXIS EXTENDING FROM THE WATERS OFF THE SOUTHEAST COAST TO
THE GREAT LAKES. THE POLAR VORTEX WILL REMAIN THE DOMINANT FEATURE
OVER EASTERN CANADA DURING THE NEW WEEK. MEANWHILE, THE TROUGH TO
OUR WEST WILL PROGRESS EASTWARD, GRADUALLY SQUEEZING THE RIDGE AND
PUSHING IT OUT OVER THE ATLANTIC. AS THE TROUGH BEGINS TO MOVE
TOWARD THE EASTERN STATES LATE IN THE WEEK, IT SHOULD BEGIN TO
INTERACT WITH THE POLAR VORTEX. ALL IN ALL, WE ARE ANTICIPATING A
RATHER UNSETTLED PERIOD.

SURFACE HIGH PRESSURE TO OUR NORTHEAST AND EAST WILL RESULT IN A
PREVAILING SURFACE FLOW FROM THE EAST TO SOUTH QUADRANT FOR SUNDAY
AND SUNDAY NIGHT. THE MOIST FLOW OFF THE OCEAN WILL LIKELY RESULT
IN A PERIOD OF LOW CLOUDS ALONG WITH A CHANCE FOR RAIN SHOWERS.

THE SURFACE FLOW IS FORECAST TO VEER TO THE SOUTH AND SOUTHWEST
FOR MONDAY AND MONDAY NIGHT CAUSING THE CLOUDS TO LIFT AND
TEMPERATURES TO WARM, RESULTING IN THE DEVELOPMENT OF UNSTABLE
CONDITIONS, ESPECIALLY AWAY FROM THE OCEAN. A FAIR AMOUNT OF LOW
LEVEL MOISTURE WILL REMAIN IN OUR REGION. AS A RESULT, WE WILL
CONTINUE TO MENTION A CHANCE OF SHOWERS AND WE WILL ALSO INCLUDE A
CHANCE OF THUNDERSTORMS FOR THE AFTERNOON AND INTO THE NIGHTTIME
HOURS ROUGHLY ALONG THE INTERSTATE 95 CORRIDOR AND AT LOCATIONS TO
THE WEST.

THE SOUTH TO SOUTHWEST FLOW WILL CONTINUE ON TUESDAY AND
TEMPERATURES ARE EXPECTED TO RISE INTO THE LOWER AND MIDDLE 80S IN
MUCH OF OUR FORECAST AREA. LINGERING LOW LEVEL MOISTURE WILL HELP
ENHANCE THE INSTABILITY AND WE ARE ANTICIPATING SCATTERED SHOWERS
AND THUNDERSTORMS, ESPECIALLY IN THE AFTERNOON AND EVENING.

A FRONTAL BOUNDARY IS FORECAST TO DROP INTO OUR REGION FROM THE
NORTH FOR TUESDAY NIGHT AND WEDNESDAY. THERE IS A FAIR AMOUNT OF
UNCERTAINTY AS TO WHETHER THE FRONT WILL REMAIN OVER OR NEAR OUR
REGION THROUGH THE BALANCE OF THE WEEK OR IF IT WILL TRY TO LIFT
BACK TO THE NORTH. REGARDLESS, UNSETTLED CONDITIONS WILL LIKELY
CONTINUE.

WHILE THERE WILL BE A CHANCE OF PRECIPITATION IN THE FORECAST FOR
EACH DAY FROM SUNDAY THROUGH FRIDAY, THE WEEK SHOULD NOT BE A
TOTAL WASHOUT. ACTUALLY, MOST OF THE TIME PRECIPITATION WILL NOT
BE FALLING. OVERALL, TEMPERATURES FOR THE WEEK SHOULD AVERAGE
ABOVE NORMAL FOR THIS TIME OF THE YEAR.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

TODAY...VFR WITH CEILINGS AROUND 10,000 FEET LOWERING SOME
THROUGH THE AFTERNOON. LIGHT AND VARIABLE WINDS, BECOMING
SOUTHEASTERLY NEAR 10 KNOTS. ANY SHOWERS ARE ANTICIPATED TO BE
SOUTH OF KILG.

TONIGHT...VFR CEILINGS TO START, THEN THESE SHOULD LOWER TO MVFR
BY ABOUT 06Z. THERE IS A CHANCE SOME IFR CEILINGS DEVELOP LATE,
HOWEVER CONFIDENCE IS LOW THEREFORE HELD OFF AT THIS TIME.
SCATTERED SHOWERS DEVELOPING FROM SOUTH TO NORTH, WITH THE
GREATEST CHANCE MAINLY FROM THE KPHL METRO ON SOUTHWARD. ANY
SHOWERS WILL LOWER THE LOCAL VISIBILITY AT TIMES. ANY FOG SHOULD
BE LIMITED AS THE MOISTURE GOES INTO A LOWERING CLOUD DECK,
THEREFORE DID NOT INCLUDE A MENTION FOR NOW. EAST-SOUTHEAST WINDS
NEAR 5 KNOTS.

OUTLOOK...
SUNDAY AND SUNDAY NIGHT...MAINLY MVFR CEILINGS WITH POSSIBLE IFR
CONDITIONS AT TIMES. A CHANCE OF SHOWERS.

MONDAY THROUGH WEDNESDAY...MAINLY VFR. HOWEVER, MVFR AND IFR
CONDITIONS ARE POSSIBLE ESPECIALLY DURING THE LATE NIGHT AND EARLY
MORNING HOURS EACH DAY. ALSO, THERE WILL BE A CHANCE OF SHOWERS
AND THUNDERSTORMS WHICH COULD LOWER CEILINGS AND REDUCE THE
VISIBILITY.

&&

.MARINE...
HIGH PRESSURE CENTERED TO OUR NORTH WILL SETTLE SOUTHWARD SOME
THROUGH TONIGHT. MEANWHILE, A FRONTAL BOUNDARY REMAINS STALLED TO
OUR SOUTH. AS A RESULT, AN EAST TO SOUTHEAST FLOW WILL BECOME
DOMINANT THROUGH TONIGHT. THE PRESSURE GRADIENT IS FORECAST TO
TIGHTEN UP SOME THIS AFTERNOON AND TONIGHT, HOWEVER THE OVERALL
WIND IS FORECAST TO NOT BE ROBUST BELOW AN INVERSION. WE ARE
ANTICIPATING SOME INCREASE AS WE GO THROUGH TONIGHT ESPECIALLY
ACROSS THE SOUTHERN WATERS AND UP DELAWARE BAY /GUSTS TO 20
KNOTS/, HOWEVER WE CONTINUE TO KEEP THE WINDS BELOW ADVISORY
CRITERIA. THE SEAS WILL GRADUALLY RESPOND TO THE WINDS, HOWEVER
PERHAPS A LITTLE SLOWER THAN WHAT WAVEWATCH GUIDANCE SUGGESTS.
THEREFORE, CONDITIONS ARE FORECAST TO REMAIN BELOW ADVISORY
CRITERIA THROUGH TONIGHT.

OUTLOOK...
HIGH PRESSURE TO OUR NORTHEAST AND EAST WILL CONTINUE TO
INFLUENCE THE COASTAL WATERS OF NEW JERSEY AND DELAWARE INTO
TUESDAY. A FRONTAL BOUNDARY FROM THE NORTH IS FORECAST TO DROP
INTO OUR REGION FOR TUESDAY NIGHT AND WEDNESDAY.

WIND SPEEDS ARE FORECAST TO REMAIN LESS THAN 25 KNOTS FROM SUNDAY
THROUGH WEDNESDAY. WAVE HEIGHTS ON OUR OCEAN WATERS MAY BUILD TO
AROUND 5 FEET ON SUNDAY AND SUNDAY NIGHT AND THEY COULD REMAIN AT
THAT LEVEL THROUGH AT LEAST WEDNESDAY AS A PERSISTENT SOUTHERLY
FLOW DEVELOPS.

&&

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

&&

$$

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