Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 310155
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
955 PM EDT SAT AUG 30 2014

.SYNOPSIS...
A FRONTAL BOUNDARY TO OUR NORTH WILL BECOME QUASI- STATIONARY
NEAR THE CANADIAN BORDER SUNDAY THROUGH TUESDAY...WITH A TROUGH
EXTENDING SOUTHWARD TO THE LEE OF THE APPALACHIANS...BETWEEN
BERMUDA HIGH PRESSURE ANCHORED OFFSHORE AND A SLOW MOVING COLD
FRONT IN THE MISSISSIPPI VALLEY. THIS VERY WEAK COLD FRONT IS
PROJECTED TO MOVE THROUGH THE REGION LATE TUESDAY INTO EARLY
WEDNESDAY...FOLLOWED BY HIGH PRESSURE RETURNING TO DOMINATE LATER
IN THE WEEK. ANOTHER COLD FRONT MAY APPROACH THE REGION EARLY NEXT
WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
NO BIG CHANGES TO THE FORECAST TONIGHT AS EVERYTHING LOOKS ON
TRACK SO FAR. THE STRATOCU THAT AFFECTED THE AREA TODAY REMAINS
ACROSS MUCH OF THE REGION, ALTHOUGH IT IS BEGINNING TO DISSIPATE
ACROSS OUR SOUTHERN AREAS. IT MAY CONTINUE TO THIN A BIT FOR THE
REST OF THE AREA OVER THE NEXT FEW HOURS, BUT WE EXPECT CLOUD
COVER TO FILL BACK IN OVERNIGHT. WE WILL REMAIN ON THE WESTERN
EDGE OF HIGH PRESSURE TO OUR EAST, LEADING TO RETURN FLOW
OVERNIGHT. THIS WILL ALLOW AN AIRMASS MODIFICATION TO CONTINUE AS
PLANNED AS DEWPOINTS WILL JUMP INTO THE MID TO UPPER 60S IN A LOT
OF SPOTS TONIGHT. STRONGER WARM AIR ADVECTION WILL ALSO TAKE PLACE
ALLOWING A LOW- LEVEL INVERSION TO SET UP. WINDS WILL GRADUALLY
DECREASE TONIGHT, LIGHTENING UP FROM THE SOUTH, TO ALLOW FOR FOG
AND A DECK OF STRATUS TO FORM.

THERE HAS BEEN A FEW SHOWERS TO OUR WEST LATE IN THE AFTERNOON AND
INTO THE EARLIER PART OF THE EVENING. HOWEVER, THEY CONTINUE TO
DISSIPATE WITH THE LOSS OF DAYTIME HEATING. GUIDANCE IS SHOWING
SOME ISOLATED SHOWERS TRYING TO WORK THERE WAY INTO THE REGION
LATE TONIGHT ON THE NOSE OF THE BETTER WAA SHOT. WE DO CARRY
SLIGHT CHANCE POPS FOR OUR WESTERN ZONES, BUT THE MODELS MAY BE
PICKING UP ON THE MOISTENING BOUNDARY LAYER AND POTENTIAL FOG
FORMATION WITH LITTLE IN THE WAY OF QPF.

OVERNIGHT LOWS WILL BE SEVERAL DEGREES WARMER THAN THE PAST FEW
MORNINGS. A BLEND OF THE MET/MAV SEEMS REASONABLE AT THIS TIME GIVING
US ABOVE NORMAL LOWS.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
CONTINUED AIRMASS MODIFICATION OCCURS AS PWATS CLIMB CLOSER TO THE 2
INCH MARK. DEWPOINTS JUMP INTO THE UPPER-60S, POSSIBLY LOW-70S
DURING THE DAY MAKING FOR MUGGY CONDITIONS. TEMPERATURES, UNDER
STRONGER WAA, SHOULD BE ABLE TO WARM INTO THE MID TO UPPER-80S
THOUGH NOT QUITE SURE HOW MUCH THE CLOUD COVER WILL PLAY A FACTOR.
WE EXPECT THE MORNING STRATUS TO LIFT AND BURN OFF WITH A STRONGER
LOW-LEVEL JET MOVING IN OVERHEAD ALLOWING FOR DEEPER MIXING. HIGHER
BASED DECKS ARE EXPECTED IN ADVANCE OF AN APPROACHING MID-LEVEL
SHORTWAVE AND SURFACE TROUGH. THESE TWO FEATURES WILL MORE THAN
LIKELY BE THE CATALYST FOR AFTERNOON AND EVENING CONVECTIVE
INITIATION.

DECENT AMOUNT SHEAR AND BOUNDARY LAYER INSTABILITY WILL BE PRESENT
AND WHEN COMBINED WITH THE ABOVE NORMAL PWATS HEAVY RAIN IS A
POSSIBILITY. THE GOOD THING ABOUT TOMORROW IS THAT THE FLOW SHOULD
BE STRONG ENOUGH TO KEEP THE STORMS MOVING, THE BAD THING IS THAT
WITH THE AVAILABLE INSTABILITY WE COULD SEE NUMEROUS TOWERS SHOOT UP
TO GIVE US SOME STRONG WET-MICROBURSTS LATER IN THE EVENING. MOST OF
THE MESOSCALE MODELS PAINT THIS SCENARIO ACROSS OUR NORTHWESTERN
ZONES, CLOSER TO THE SHORTWAVE PASSAGE. WE WILL CONTINUE TO WATCH
THE DEVELOPMENT FOR ANY LOCALIZED FLOOD AND SEVERE ISSUES.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
SUNDAY NIGHT....BIG CONCERN THROUGH THIS PERIOD WILL BE THE
CONVECTION. THE UPPER LEVEL TROUGH OVER THE UPPER MID WEST NOW
WILL BE LIFTING OVER THE NORTHEAST U.S. BY TOMORROW NIGHT.
HOWEVER, ALL MODELS SHOW THE TROUGH FILLING AS IT LIFTS, WHICH IS
CONSISTENT WITH WHAT WAS OBSERVED WITH THE 12Z SOUNDINGS THIS
MORNING, WHICH SHOWED VERY MARGINAL HEIGHT FALLS AHEAD OF THE
TROUGH AXIS. AS MENTIONED BY THE PREVIOUS SHIFT, PWAT VALUES ARE
EXPECTED TO BE ABOVE NORMAL, NEAR 2 INCHES. HOWEVER, AS MENTIONED
PREVIOUSLY WITH MEAN FLOW OF NEAR OR ABOVE 30 KT...STORM MOTIONS
SHOULD BE RELATIVELY FAST AND AS MENTIONED IN THE PREVIOUS
DISCUSSION, WE STILL HAVE RELATIVELY DRY ANTECEDENT CONDITIONS.
THUS DON`T ANTICIPATE WIDESPREAD ISSUES OUTSIDE OF SOME POOR
DRAINAGE/URBAN NUISANCE FLOODING AT THIS TIME. AS FOR THE SEVERE
THREAT, CAPE VALUES (BOTH SURFACE BASED OR ELEVATED - WHICH MAY BE
MORE REALISTIC FOR THE NIGHT TIME HOURS) COULD BE NEAR OR ABOVE
500 J/KG. AT THE SAME TIME, BULK SHEAR (MOSTLY SPEED SHEAR) COULD
BE NEAR 30KT. THIS COULD BE ENOUGH FOR STRONG OR EVEN MARGINALLY
SEVERE STORMS FOR WINDS, AND POSSIBLY ENOUGH FOR SOME SMALL HAIL.

LABOR DAY...THERE MAY BE A BRIEF BREAK IN THE CONVECTION (OR AT
LEAST MORE LIMITED COVERAGE) AS THE 500MB SHORT WAVE RIDGE AXIS
MOVES OVER. AS IT DOES SO, MEAN FLOW WILL DECREASE, HOWEVER PWAT
VALUES WILL LIKELY ALSO DECREASE AS THE FLOW TURNS MORE WESTERLY.
THUS, THINK THE FLOODING THREAT WILL REMAIN MORE OF A URBAN AND
POOR DRAINAGE THREAT.

TUESDAY INTO WEDNESDAY...EXPECT A LULL IN THE PRECIPITATION
CHANCES BEFORE THE NEXT UPPER LEVEL TROUGH (AT THIS TIME OVER THE
GREAT BASIN REGION) SLIDES EAST, AS DOES THE ASSOCIATED SURFACE
COLD FRONT. GFS AND ECMWF SPED UP THE TIMING OF THE COLD FRONT
WITH THE LATEST RUNS...NOW ARRIVING AS EARLY AS TUESDAY EVENING.
IN THE WAKE OF THE FRONT, EXPECT DRIER AND COOLER WEATHER, THOUGH
TEMPERATURES WILL LIKELY STILL BE SLIGHTLY ABOVE NORMAL.

THURSDAY THROUGH SATURDAY...UPPER LEVEL FLOW TRANSITIONS TO MOSTLY
ZONAL FLOW BY THURSDAY WITH A SURFACE HIGH SETTLING IN THROUGH
FRIDAY. BY SATURDAY THE NEXT UPPER LEVEL TROUGH PROPAGATES EAST
ACROSS SOUTHERN CANADA. THERE IS UNCERTAINTY HOWEVER, GIVEN THE
MOSTLY ZONAL FLOW IF THE ASSOCIATED COLD FRONT WILL DIG AS FAR
SOUTH AS OUR REGION BEFORE FRONTOLYSIS OCCURS. FOR NOW, HAVE A
SLIGHT CHANCE FOR THUNDERSTORMS THROUGH THE WEEKEND GIVEN THE
UNCERTAINTY.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

TONIGHT...VFR EARLY, LOWERING TO MVFR AFTER MIDNIGHT. MODEL
GUIDANCE CONTINUES TO SHOW IFR CIGS DEVELOPING, SO WE HAVE
INCLUDED IFR CIGS AT A FEW MORE SITES TOWARD DAYBREAK. WINDS
LIGHTEN SOME, BUT REMAIN SOUTH TO SOUTHEASTERLY. AS MOISTURE
INCREASES OVERNIGHT, SOME LIGHT FOG MAY ALSO DEVELOP IN ADDITION
TO THE CIGS.

TOMORROW...LOWER CIGS/VSBYS WILL LIFT BACK TO VFR BY MID-LATE
MORNING. SHOWERS AND POTENTIAL THUNDER SHOULD INCREASE LATE IN
THE DAY INTO THE EVENING FROM WEST TO EAST. WHEN/WHERE
THUNDERSTORMS OCCUR IS UNCERTAIN AT THIS TIME, SO THEY WERE LEFT
OUT OF THE 00Z TAFS, ALTHOUGH A MODERATE SHOWER GROUP WAS INSERTED.
WHERE ANY SHOWERS OR THUNDERSTORMS OCCUR, THEY COULD TEMPORARILY
REDUCE CIGS/VSBYS.

OUTLOOK...
SUNDAY NIGHT INTO MONDAY NIGHT...IFR CONDITIONS EXPECTED WITH
SHOWERS AND THUNDERSTORMS. COVERAGE OF PRECIPITATION DECREASING BY
MONDAY NIGHT.

TUESDAY AND TUESDAY NIGHT...CONDITIONS IMPROVING TO VFR EARLY IN THE
DAY. STILL A SMALL THREAT OF SHOWERS AND THUNDERSTORMS.

WEDNESDAY THROUGH THURSDAY...GENERALLY VFR CONDITIONS EXPECTED.

&&

.MARINE...
SUB-SCA CONDITIONS EXPECTED TONIGHT AND A MAJORITY OF TOMORROW. SEAS
WILL CONTINUE TO BUILD THROUGH SUNDAY UNDER A STRENGTHENING
SOUTHERLY FLOW THAT BEGINS TO BACK TOWARDS THE SOUTHWEST LATER
TOMORROW. THIS COULD POSE SOME ISSUES AROUND THE INLETS WHERE LARGER
SWELLS, CLOSE TO 5 FEET, AND GUSTS AROUND 25 KNOTS MAY
OCCUR...MOSTLY NEARSHORE FOR THE GUSTS. DECIDED THE SETUP WAS TOO
MARGINAL TO WARRANT A SMALL CRAFT AT THIS TIME.

OUTLOOK...
MONDAY NIGHT...WINDS AND SEAS SHOULD REMAIN JUST BELOW SMALL CRAFT
ADVISORY CRITERIA. GUSTIER WINDS POSSIBLE IN THE VICINITY OF
THUNDERSTORMS.

TUESDAY THROUGH THURSDAY...WINDS AND SEAS EXPECTED TO REMAIN WELL
BELOW SCA CRITERIA. HOWEVER, SOME GUSTY WINDS ARE POSSIBLE WITH
THUNDERSTORMS ON TUESDAY.

&&

.RIP CURRENTS...
THE RIP CURRENT RISK FOR SUNDAY IS FORECAST TO BE LOW. HOWEVER, IF
THE SWELL HEIGHT INCREASES AND/OR THE PERIOD BECOMES LONGER THAN
EXPECTED, THE RISK COULD INCREASE TO MODERATE.

&&

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

&&

$$
SYNOPSIS...FRANCK
NEAR TERM...HEAVENER/ROBERTSON
SHORT TERM...HEAVENER
LONG TERM...JOHNSON
AVIATION...HEAVENER/JOHNSON/ROBERTSON
MARINE...HEAVENER/JOHNSON
RIP CURRENTS...






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