Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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876
FXUS61 KPHI 160153
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
953 PM EDT FRI MAY 15 2015

.SYNOPSIS...
HIGH PRESSURE WILL BE OFFSHORE THROUGH SATURDAY. LOW PRESSURE FROM
THE UPPER MISSISSIPPI VALLEY WILL MOVE NORTHEASTWARD, WITH AN
ASSOCIATED WARM FRONT CROSSING OUR REGION TONIGHT. A COLD FRONT WILL
THEN SETTLE THROUGH OUR AREA LATE SUNDAY. THE NEXT AREA OF LOW
PRESSURE FROM THE ROCKIES SHOULD TRACK NORTHEASTWARD THROUGH THE
GREAT LAKES REGION, PULLING A COLD FRONT ACROSS OUR AREA TUESDAY.
HIGH PRESSURE WILL THEN GRADUALLY BUILD TOWARD OUR REGION WEDNESDAY
INTO FRIDAY.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
HIGH PRESSURE WAS ANCHORED OFF THE MID-ATLANTIC COAST THIS EVENING.
MEANWHILE, A SURFACE LOW WAS LOCATED ON THE LEE SIDE OF THE CENTRAL
ROCKIES AND A CONSIDERABLY WEAKER LOW PRESSURE SYSTEM OVER THE GREAT
LAKES. THE WEATHER PATTERN FOR OUR REGION WILL BE INFLUENCED
MAINLY BY THE OFFSHORE HIGH WITH BROAD SOUTHERLY RETURN FLOW
TONIGHT. LOOKING ALOFT, RIDGING WILL PERSIST OVER THE EASTERN
CONUS WITH S-N RIDGE AXIS CENTERED TO OUR WEST NEAR THE
APPALACHIAN SPINE. THERE ARE SEVERAL WEAK SHORTWAVE TROUGHS
ROTATING ALONG THE NORTHERN PERIPHERY OF THE RIDGE, WHICH COULD BE
ACCOMPANIED BY A FEW SHOWERS TONIGHT AS THEY MOVE THROUGH THE
FORECAST AREA.

DID NOT RAISE POPS MUCH FOR THIS EVENING SINCE THE BULK OF THESE
SHOWERS HAVE TENDED TO DISSIPATE AS THEY MOVE EASTWARD INTO A
MUCH DRIER AIRMASS THAT IS IN PLACE OVER THE FORECAST AREA.
DEWPOINTS AT 01Z WERE MAINLY IN THE 40S AND EVEN 30S IN SOME SPOTS
ACROSS THE FORECAST AREA. SOUTHERLY FLOW AT THE SURFACE AND
WESTERLY FLOW IN THE LOW-LEVELS WILL HELP MOISTEN THE BOUNDARY
LAYER GRADUALLY THROUGHOUT THE NIGHT. EXPECT DEWPOINTS TO BE IN
THE 50S AND EVEN LOWER 60S BY DAYBREAK TOMORROW MORNING BASED ON
CURRENT UPSTREAM OBSERVATIONS IN VA AND WESTERN PA. ACCORDINGLY,
THE ENVIRONMENT MAY BE SLIGHTLY MORE CONDUCIVE FOR SHOWERS LATE
TONIGHT GIVEN THE INCREASING MOISTURE, BUT COVERAGE SHOULD STILL
BE WITHOUT STRONG/ ORGANIZED FORCING FOR ASCENT.

THE DEVELOPMENT OF FOG TONIGHT DOES NOT SEEM PARTICULARLY FAVORABLE
DUE TO PERSISTENT MID AND HIGH CLOUDS STREAMING OVERHEAD AND GIVEN
HOW DRY THE AIRMASS IS INITIALLY. HOWEVER, THE LAMP GUIDANCE
CONTINUES TO BE AGGRESSIVE WITH IT.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
THE FRONTAL BOUNDARY TO OUR NORTH WILL BE CLOSE ENOUGH AS
MOISTURE CONTINUES TO INCREASE TO INCLUDE A CHANCE OF AFTERNOON
THUNDERSTORMS SATURDAY AFTERNOON. ALSO, THE SET-UP ONCE AGAIN LOOKS
FAVORABLE FOR MIXING AND SOME SSW WIND GUSTS CLOSE TO 20 MPH IN THE
AFTERNOON. AREAS ACROSS NORTHERN NJ AND EASTERN PA HAVE THE HIGHEST
CHANCE OF SEEING AFTERNOON AND EVENING POP UP THUNDERSTORMS.
EVEN THOUGH WE HAVE BEEN DRY RECENTLY, PW VALUES WILL INCREASE TO
OVER 1.5 INCHES RESULTING IN HEAVY DOWNPOURS FROM ANY
THUNDERSTORMS. INSTABILITY LOOKS MARGINAL OVERALL, CHARACTERIZED
BY 1000 OR SO MODELED J/KG CAPE. HOWEVER, 0-6 KM BULK SHEAR IS
MODELED TO BE FAIRLY WEAK. OVERALL, INSTABILITY LOOKS SUFFICIENT
FOR SOME THUNDERSTORM DEVELOPMENT ACROSS THE REGION BUT STORM WILL
BE LIMITED WITH MORE OF A PULSE SET-UP LIKELY. AS USUAL, THE NAM
IS MOST AGGRESSIVE SHOWING STEEP LOW LEVEL LAPSE RATES AND SOME
MID-LEVEL DRY AIR WHICH MAY LEAD TO DOWNDRAFTS AND STRONGER WIND
GUSTS IN THE THUNDERSTORMS. THE GFS IS QUITE A BIT MORE STABLE
ATTM. CURRENT THINKING IS THAT SCATTERED STORMS WILL DEVELOP IN
THE AFTERNOON, MORE NUMEROUS CLOSER TO THE FRONT AND BE OF PULSE
NATURE. SPC HAS A MARGINAL RISK AS WELL FOR ANY SEVERE THREAT
TOMORROW AFTERNOON. 925 MB TEMPERATURES ALSO SUGGEST HIGH
TEMPERATURES FORECASTED ON MOST NUMERICAL GUIDANCE SETS LOOK TO
LOW. WILL GO HIGHER WITH FORECASTED HIGH TEMPERATURES, IN THE MID
80`S THAT ARE CONVECTION DEPENDENT.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
THE SYNOPTIC SETUP IS COMPRISED OF AN UPPER-LEVEL TROUGH IN THE WEST
THAT MIGRATES EAST-NORTHEASTWARD WITH TIME AND AN UPPER-LEVEL RIDGE
IN THE EAST. THE RIDGE REMAINS IN PLACE INTO TUESDAY BEFORE
FLATTENING OUT AS A TROUGH MOVES ACROSS THE MIDWEST AND GREAT LAKES.
THIS TROUGH SLIDES ACROSS THE NORTHEAST WEDNESDAY THEN THE FLOW
TURNS MORE ZONAL IN ITS WAKE. THE REGION REMAINS RATHER DRY AND
THERE ARE SOME OPPORTUNITIES FOR RAIN, GENERALLY CENTERED ON SUNDAY
AND LATE MONDAY AND TUESDAY. THE LATTER IS ASSOCIATED WITH A COLD
FRONT THAT IS FORECAST TO SWEEP ACROSS THE AREA TUESDAY. WE USED A
MODEL BLEND FOR SATURDAY NIGHT THROUGH MONDAY, THEN THE 12Z WPC
GUIDANCE OR SUPERBLEND THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE
FOLLOWING ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES.

FOR SATURDAY NIGHT AND SUNDAY...THE RIDGE AXIS SHOULD BE APPROACHING
THE AREA SUNDAY MORNING. AN UPPER-LEVEL TROUGH AMPLIFIES ACROSS NEW
ENGLAND AND THIS WILL SEND A FRONTAL BOUNDARY OUR WAY LATE SUNDAY,
BASICALLY IN THE FORM OF A BACKDOOR FRONT AS HIGH PRESSURE BECOMES
ESTABLISHED NEAR THE CANADIAN MARITIMES. FIRST, LINGERING CONVECTION
MAY OCCUR SATURDAY EVENING THEN THIS SHOULD DISSIPATE AS THE NIGHT
WEARS ON. GIVEN THE SYNOPTIC SETUP ON SUNDAY, THE BETTER INSTABILITY
IS FORECAST TO BE PUSHED FARTHER INLAND AND NOT AS HIGH GIVEN SOME
WARMING ALOFT. THE CONVECTION THAT DOES FORM MAY TEND TO BE SLOW
MOVING AS THE FLOW WEAKENS WITH THE RIDGE AXIS NEARLY OVER OUR AREA
DURING SUNDAY, AND WITH PW VALUES OF 1.50-2.00 INCHES LOCALLY HEAVY
RAIN WILL BE POSSIBLE. THE RAIN WOULD BE WELCOMED SINCE THE REGION
CONTINUES TO BE RATHER DRY. ANY CONVECTION SHOULD LESSEN OR EVEN
DISSIPATE SUNDAY NIGHT, THEN A BACKDOOR FRONT MAKES ITS WAY ACROSS
THE AREA AS HIGH PRESSURE STRENGTHENS SOME AND EXTENDS INTO THE
NORTHERN MID ATLANTIC. THIS WILL RESULT IN COOLING FROM AN OCEAN
INFLUENCE SUNDAY NIGHT WITH PERHAPS SOME LOW CLOUDS DEVELOPING. WE
WENT A LITTLE ABOVE MOS GUIDANCE FOR HIGH TEMPERATURES ON SUNDAY AS
THE MODELS MAY BE OVERDOING THE CLOUD COVER.

FOR MONDAY AND TUESDAY...AN UPPER-LEVEL TROUGH IS FORECAST TO BE
LIFTING ACROSS THE GREAT LAKES REGION MONDAY AND ACROSS SOUTHEASTERN
CANADA TUESDAY. THIS WILL DRIVE A COLD FRONT EASTWARD, WHICH SHOULD
CLEAR OUR COAST DURING TUESDAY AS THE UPPER-LEVEL RIDGE FLATTENS
OUT. WE WILL START THE DAY MONDAY WITH AN ONSHORE FLOW BEFORE
SURFACE HIGH PRESSURE SHIFTS EAST AND THE FLOW STARTS TO VEER SOME
AHEAD OF A COLD FRONT. THE INSTABILITY AXIS TO OUR WEST SHOULD MOVE
EASTWARD AHEAD OF THE FRONT, HOWEVER THE INITIAL ONSHORE FLOW SHOULD
TEMPER THAT TO SOME EXTENT. THE PW VALUES ARE FORECAST TO REMAIN
ABOUT IN THE 1.50-2.00 INCH RANGE DESPITE SOME LOW-LEVEL
COOLING/STABILIZATION FROM THE ONSHORE FLOW. THERE MAY NOT BE A LOT
OF CONVECTION AROUND ON MONDAY BUT THIS WILL DEPEND ON THE EXTENSION
OF SURFACE HIGH PRESSURE INTO OUR AREA FROM THE NORTHEAST. WE
CONTINUED THE HIGHER POPS ACROSS THE WESTERN ZONES CLOSER TO THE
BETTER INSTABILITY. THE UPPER-LEVEL FEATURE IS FORECAST TO TRACK
WELL TO OUR NORTHWEST SO THIS MAY REMOVE OUR AREA FROM THE BEST
LARGE SCALE LIFT. THERE SHOULD BE MORE COVERAGE OF CONVECTION ON
TUESDAY AS A COLD FRONT ARRIVES WITH A MOIST ENVIRONMENT WITH SOME
INSTABILITY IN PLACE. THE MAIN DYNAMICS THOUGH MAY FOCUS MORE
FARTHER NORTH.

FOR WEDNESDAY THROUGH FRIDAY...AN UPPER-LEVEL TROUGH SETTLES ACROSS
THE NORTHEAST ESPECIALLY DURING WEDNESDAY BEFORE THE FLOW STARTS TO
TURN MORE ZONAL. AT THE SURFACE, HIGH PRESSURE IS FORECAST TO
GRADUALLY START BUILDING TOWARD OUR AREA DURING THIS TIME FRAME. A
PERIOD OF CAA OCCURS THOUGH FOLLOWING THE COLD FRONTAL PASSAGE
TUESDAY, AND THIS ALONG WITH A TIGHTENED PRESSURE GRADIENT MAY
RESULT IN BREEZY CONDITIONS WEDNESDAY INTO THURSDAY. THE UPPER-LEVEL
FLOW MAY SHARPEN SOME FRIDAY AND WITH A BOUNDARY STALLED WELL TO OUR
SOUTH SOME ENERGY MAY TRY AND TRACK ALONG IT. AS OF NOW, HIGH
PRESSURE IS FORECAST TO BE CLOSE ENOUGH TO OUR AREA THEREFORE WE
WENT WITH A DRY FORECAST ATTM.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

PREDOMINATELY VFR THRU MOST THE TAF PERIOD. S WINDS HAVE LOST
THEIR GUSTINESS THIS EVE AFTER SUNSET. DID NOT HAVE THE CONFIDENCE
TO MENTION SHRA IN THE TAFS FOR TONIGHT AND SATURDAY BUT THERE IS
A SLIGHT CHANCE FOR A PASSING SHRA THRU THE MORNING. CHANCES
INCREASE SLIGHTLY FROM WEST TO EAST IN THE AFTERNOON, ESPECIALLY
LATE IN THE DAY BUT FORECAST COVERAGE OF 30-40 PERCENT TOO LOW TO
INCLUDE THIS FAR OUT. SAME GOES FOR THUNDERSTORMS, BUT THERE IS A
CHANCE OF TSRA DURING THE AFTERNOON AND EARLY EVENING. FUTURE TAF
ISSUANCES WILL HAVE THE OPPORTUNITY TO ADD SHRA/TSRA IN AS
CERTAINTY INCREASES. S-SW WIND MAY GUST TO AROUND 20 KNOTS LATE
IN THE AFTERNOON ON SATURDAY.

OUTLOOK...
SATURDAY NIGHT AND SUNDAY...SOME SHOWERS AND THUNDERSTORMS AROUND
WITH POTENTIALLY TIMES OF MVFR/IFR, OTHERWISE VFR. THE GREATER
CHANCE SHOULD BE INLAND.

MONDAY AND TUESDAY...SOME LOW CLOUDS AND SHOWERS POSSIBLE TO START
MONDAY, OTHERWISE TIMES OF MVFR/IFR WITH SOME SHOWERS AND
THUNDERSTORMS ESPECIALLY DURING TUESDAY WITH A COLD FRONT.

WEDNESDAY...VFR OVERALL.

&&

.MARINE...
CONTINUED SOUTHERLY TO SOUTHWESTERLY WINDS UNDER SCA CRITERIA. WIND
GUSTS MAY PEAK AROUND 20 KNOTS SATURDAY AFTERNOON. SEAS WILL BE
BUILDING AS WELL, REACHING FOUR FEET BY SATURDAY AFTERNOON.

OUTLOOK...
SATURDAY NIGHT AND SUNDAY...A SOUTHWEST FLOW AHEAD OF A COLD FRONT
WILL BUILD THE SEAS SOME, HOWEVER THE CONDITIONS OVERALL ARE
ANTICIPATED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA. THE WINDS
START TO BECOME ONSHORE SUNDAY NIGHT FROM NORTH TO SOUTH AS A
BACKDOOR FRONT MOVES THROUGH.

MONDAY AND TUESDAY...THE WINDS AND SEAS MAY NEAR ADVISORY CRITERIA
ON THE COASTAL WATERS AS THE FLOW IS ONSHORE MONDAY, THEN WEAKENS
SOME TUESDAY AS A COLD FRONT ARRIVES. DENSE FOG IS NOT ANTICIPATED
WITH THE ONSHORE FLOW ATTM.

WEDNESDAY...NORTHWESTERLY FLOW MAY BE A BIT GUSTY ESPECIALLY IN THE
MORNING, OTHERWISE CONDITIONS ARE ANTICIPATED TO BE BELOW ADVISORY
CRITERIA.

&&

.RIP CURRENTS...
THE RISK FOR RIP CURRENTS IS BORDERLINE LOW TO MODERATE FOR THE
NJ COAST ON SATURDAY AFTERNOON.

&&

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

&&

$$
SYNOPSIS...GORSE
NEAR TERM...KLEIN
SHORT TERM...GAINES
LONG TERM...GORSE
AVIATION...GAINES/GORSE/KLEIN
MARINE...GAINES/GORSE
RIP CURRENTS...KLEIN



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