Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 020735
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
335 AM EDT MON MAY 2 2016

.SYNOPSIS...
LOW PRESSURE AND ITS ASSOCIATED FRONTS WILL AFFECT OUR AREA TODAY
AND TONIGHT. ANOTHER LOW PRESSURE SYSTEM WILL SLIDE UP ACROSS THE
DELMARVA ON TUESDAY AND THEN OFFSHORE TUESDAY NIGHT. WEAK HIGH
PRESSURE WILL RIDGE ACROSS THE AREA WEDNESDAY BEFORE ANOTHER LOW
PRESSURE SYSTEM ARRIVES FROM THE GREAT LAKES. THIS LOW WILL MEANDER
ACROSS THE AREA THROUGH THE END OF THE WEEK AND INTO THE EARLY PART
OF THE UPCOMING WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A FRONTAL BOUNDARY STILL DRAPED TO OUR SOUTH ALONG WITH HIGH
PRESSURE TO OUR NORTHEAST IS KEEPING A RATHER MOIST ONSHORE FLOW
ACROSS OUR AREA. THIS IS RESULTING IN SOME FOG AND DRIZZLE. IT
APPEARS THAT ANY DENSE FOG IS MAINLY CONFINED TO THE HIGHER TERRAIN
GIVEN HOW LOW THE CEILINGS ARE EARLY THIS MORNING. SOME SUBTLE SHORT
WAVES WITHIN THE SOUTHWESTERLY FLOW ALOFT IS HELPING TO GENERATE
SOME SHOWERS, WITH ONE OF THESE MORE NOTABLE FEATURES MOVING THROUGH
EARLY THIS MORNING. THIS SHOULD KEEP SOME SHOWERS AROUND THE AREA
BEFORE A LULL TAKES PLACE. THE FORECAST THEREAFTER IS RATHER
COMPLICATED WITH LESS CERTAINTY GIVEN IT HINGES ON WHERE THE WARM
FRONT MOVES TO BY LATE THIS AFTERNOON. WE ARE EXPECTING MUCH WARMER
AIR TO MOVE INTO AT LEAST OUR DELMARVA ZONES, HOWEVER THE EXTENT OF
EROSION OF THE LOW CLOUDS IS NOT ALL THAT CLEAR.

AN EXAMINATION OF THE MODEL GUIDANCE SUGGESTS THE WARM FRONT MAY GET
INTO THE PHILADELPHIA METRO AREA, WITH THE MAIN WARM SECTOR HANGING
BACK FARTHER TO THE SOUTH. THE FLOW IN THE LOWEST LEVELS IS NOT
FORECAST TO BE ALL THAT STRONG AS AN INCOMING SURFACE LOW IS ON THE
WEAKER SIDE. AS A RESULT, WE ARE NOT RUSHING IN THE CLEARING FROM
SOUTH TO NORTH. THIS WILL HAVE AN IMPACT ON DESTABILIZATION THROUGH
THE AFTERNOON, AT WHICH THE BULK OF IT IS ACROSS PORTIONS OF
MARYLAND AND DELAWARE TO PERHAPS FAR SOUTHERN NEW JERSEY. AGAIN,
THIS WILL ULTIMATELY DEPEND ON THE POSITIONING OF THE INCOMING WARM
FRONT. THIS WILL ALSO DETERMINE THE EXTENT OF CONVECTIVE CHCS AS
ANOTHER SHORT WAVE ARRIVES TOWARD EVENING ALONG WITH THE INCOMING
WEAK SURFACE LOW. THE FORCING FOR ASCENT SHOULD INCREASE WITH THESE
FEATURES WITH AN INCREASE IN SHOWERS AND PERHAPS THUNDERSTORMS.

WE CONTINUED TO CONFINE THE THUNDER CHCS ACROSS THE SOUTHERN
PORTIONS OF OUR CWA, HOWEVER DID NOT ADD IN ENHANCED WORDING YET
GIVEN LESS CONFIDENCE WITH THE AMOUNT OF CLEARING AND THEREFORE
INSTABILITY. IF HIGHER INSTABILITY DEVELOPS, SOME STORMS COULD
PRODUCE LOCALLY STRONG WINDS WITH THE FORECAST SOUNDINGS INDICATING
THE POTENTIAL FOR SOME WET MICROBURSTS. THE LOW-LEVEL FLOW WILL BE
BACKED SOME NEAR THE WARM FRONT WHICH WILL NEED TO BE MONITORED IF
CONVECTIVE CELLS INTERACT WITH IT. OVERALL, THE POTENTIAL IS THERE
FOR SOME GUSTY THUNDERSTORMS ALONG WITH SOME HAIL HOWEVER THE AMOUNT
OF DESTABILIZATION IS IN QUESTION.

AS FOR THE HIGH TEMPERATURES, WE USED A MOS BLEND OVERALL ALONG WITH
CONTINUITY. THIS CONTINUES TO INDICATE A STRONG GRADIENT FROM SOUTH
TO NORTH. THE HOURLY GRIDS EARLY THIS MORNING WERE ADJUSTED BASED ON
THE LATEST OBSERVATIONS AND THEN THE LAMP/LAV GUIDANCE WAS BLENDED
IN.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
AS A BIT MORE CONSOLIDATED SHORT WAVE ENERGY SLIDES NORTHEASTWARD,
SURFACE LOW PRESSURE IS FORECAST TO MOVE ACROSS THE AREA TONIGHT.
THIS SHOULD HELP SERVE BETTER FOCUS FOR LIFT AND THEREFORE WE ARE
ANTICIPATING THAT SHOWERS EXPAND IN COVERAGE WITH THE POTENTIAL FOR
SOME LOCALLY HEAVY DOWNPOURS. A RIBBON OF ENHANCED LIFT MAY BE CLOSE
TO THE INTERSTATE 95 CORRIDOR.

THE EVENING MAY START CONVECTIVELY ACTIVE ACROSS OUR SOUTHERN ZONES
AS CONVECTION THAT DEVELOPS TO OUR SOUTHWEST TRACKS OUR WAY.
THIS MAY BE ALONG A LEE SIDE TROUGH AND ALSO NEAR A POTENTIAL
HEATING DIFFERENTIAL BOUNDARY IN CLOSE PROXIMITY TO A WARM FRONT.
THE CONVECTIVE COVERAGE WILL BE DRIVEN BY THE AMOUNT OF INSTABILITY,
HOWEVER EARLY ON THERE COULD BE SOME DISCRETE CELLS BEFORE
CONSOLIDATION OCCURS. AS MENTIONED IN THE NEAR TERM SECTION, THE
INTENSITY OF THE CONVECTION WILL BE DETERMINED ON THE NORTHWARD
EXTENT OF THE WARM SECTOR. GIVEN THE QPF FORECAST AND THE INCOMING
SHORT WAVE AND ASSOCIATED LIFT, THE POPS WERE INCREASED INTO THE
CATEGORICAL RANGE THROUGH THE NIGHT FOR MUCH OF THE CWA.

AS FOR THE LOW TEMPERATURES, WE USED A MOS BLEND OVERALL. A MILDER
NIGHT IS ANTICIPATED ESPECIALLY FOR THE CENTRAL AND SOUTHERN ZONES
GIVEN AN INCOMING WARM SECTOR. THIS WILL DRIVE DEW POINTS UP AS
WELL. GIVEN THE AMOUNT OF SHOWER ACTIVITY ANTICIPATED, ANY
SIGNIFICANT FOG SHOULD BE PATCHY DESPITE THE INCREASING DEW POINTS
FOR AWHILE.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
THE FRONT THAT CROSSES THROUGH THE FORECAST AREA DURING THE SHORT
TERM WILL BE SOUTH OF THE REGION TUESDAY MORNING. LOW PRESSURE WILL
DEVELOP ALONG THE FRONT OVER NC/VA AND MOVE NORTHEAST OFF THE DE
COAST BY TUESDAY NIGHT. THIS WILL RESULT IN MORE RAINY WEATHER FOR
TUESDAY. POPS FOR TUE WERE KEPT IN THE HIGH LIKELY/LOW CATEGORICAL
RANGE FOR MOST AREAS WITH THE CHC POPS ACROSS THE N/W AREAS..FARTHER
AWAY FROM THE RAINY SYSTEM.

WEAK RIDGING WILL OCCUR ACROSS THE AREA LATER TUESDAY NIGHT AND INTO
WEDNESDAY BEHIND THE DEPARTING LOW. THE BRIEFLY LOWER POPS WILL NOT
REMAIN LOW LONG AS THE NEXT SYSTEM APPROACHES FROM THE GREAT LAKES.

A BIG PATTERN CHANGE ALREADY TAKING PLACE EARLY THIS WEEK BEGINS TO
AFFECT OUR WEATHER LATER WEDNESDAY AS H5 UPPER HEIGHTS FALL RAPIDLY
ACROSS THE GREAT LAKES. LOW PRESSURE DEVELOPS WITH THESE HEIGHT
FALLS AND CIRCULATES ACROSS OUR AREA FROM WEDNESDAY NIGHT INTO THE
EARLY PART OF THE WEEKEND. MUCH OF THE PERIOD WILL HAVE CLOUDS AND
SHOWERS. WE HAVE KEPT POPS IN THE CHC RANGE FOR NOW...BUT EXPECT
HIGHER POPS WHEN THE DETAILS BECOME MORE CERTAIN LATER TODAY AND
TUESDAY. TEMPERATURES WILL REMAIN GENERALLY ABOUT 4 TO 7 DEGREES
BELOW NORMAL.

&&

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

TODAY...LIFR/IFR CEILINGS ARE EXPECTED TO CONTINUE FOR AWHILE THIS
MORNING, WITH SOME IMPROVEMENT TO MVFR THIS AFTERNOON. WHILE AT
LEAST SOME ADDITIONAL IMPROVEMENT IS POSSIBLE LATER THIS AFTERNOON,
ESPECIALLY NEAR AND SOUTH OF KPHL, CONFIDENCE IS LOW ON HOW FAR
NORTH A WARM FRONT GETS. THE VISIBILITIES WILL BE MVFR TO LOCALLY
IFR THIS MORNING WITH SOME IMPROVEMENT EXPECTED BY MIDDAY. SOME
DRIZZLE ALONG WITH SHOWERS ARE EXPECTED THIS MORNING, THEN SHOWERS
AGAIN TOWARD LATER THIS AFTERNOON.

SOME THUNDERSTORMS ARE POSSIBLE MOSTLY SOUTH AND WEST OF
PHILADELPHIA LATER THIS AFTERNOON, HOWEVER THIS WILL DEPEND ON THE
AMOUNT OF CLEARING THAT CAN OCCUR. EAST-NORTHEAST WINDS 5-10 KNOTS,
BECOMING SOUTHEAST TO LOCALLY SOUTH, THEN TURNING EASTERLY AGAIN
TOWARD EVENING.

TONIGHT...IFR TO LIFR CEILINGS AS PLENTY OF MOISTURE REMAINS. IF A
WARM FRONT IS FARTHER NORTH TO START THIS EVENING, CEILINGS COULD BE
AT LEAST A LITTLE HIGHER. SHOWERS ARE EXPECTED WHICH WILL REDUCE THE
VISIBILITY AT TIMES, WITH PERHAPS A FEW THUNDERSTORMS IN THE EVENING
MAINLY SOUTH OF KPHL. MOSTLY NORTHEAST WINDS IN THE 4-8 KNOT RANGE.

OUTLOOK...
TUE/TUE NIGHT...MVFR OR IFR CONDITIONS ACROSS MOST OF THE DEL
VALLEY...DELMARVA AND SRN NJ. OCNL RAIN AND FOG POSSIBLE.
WED THRU FRI...MOSTLY VFR BUT LOWER CONDITIONS IN SCT SHOWERS.

&&

.MARINE...
AN ONSHORE FLOW CONTINUES TODAY AND TONIGHT, HOWEVER THIS SHOULD
SHIFT TO SOUTHERLY FOR A TIME ACROSS OUR SOUTHERN WATERS BY LATER
TODAY AND THIS EVENING WITH THE ARRIVAL OF A WARM FRONT. THE FLOW
OVERALL REMAINS ON THE LIGHTER SIDE. IT CONTINUES TO BE RATHER
MARGINAL REGARDING SEAS ESPECIALLY ACROSS THE SOUTHERN COASTAL
WATERS, HOWEVER WILL KEEP THE SMALL CRAFT ADVISORY GOING FOR NOW. IT
GOES UNTIL 4 PM TODAY. OTHERWISE, WINDS ARE EXPECTED TO REMAIN BELOW
25 KNOTS.

SOME SHOWERS ARE EXPECTED TODAY WITH THESE BECOMING MORE NUMEROUS
TONIGHT. A FEW THUNDERSTORMS ARE POSSIBLE MAINLY LATE THIS AFTERNOON
AND THIS EVENING ACROSS OUR SOUTHERN WATERS, AND IF THESE DO OCCUR
THEN LOCALLY GUSTY WINDS WILL BE POSSIBLE.

OUTLOOK...
WINDS AND SEAS SHOULD REMAIN MOSTLY BELOW SMALL CRAFT CRITERIA.
OCCASIONAL SHOWERS EXPECTED THRU THE PERIOD.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 4 PM EDT THIS
     AFTERNOON FOR ANZ450>455.

&&

$$
SYNOPSIS...O`HARA
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...O`HARA
AVIATION...GORSE/O`HARA
MARINE...GORSE/O`HARA


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