Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 172007
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
407 PM EDT SUN AUG 17 2014

.SYNOPSIS...
A COLD FRONT CLEARING THE AREA TO THE SOUTH TONIGHT WILL
STALL OVER THE LOWER DELMARVA ON MONDAY. A WAVE OF LOW PRESSURE
WILL TRACK EASTWARD ALONG THE STALLED BOUNDARY MONDAY NIGHT AND
MOVE OFFSHORE TUESDAY. THE FRONTAL BOUNDARY SHOULD REMAIN NEARLY
STATIONARY FROM THE GREAT LAKES TO THE SOUTHERN MIDDLE ATLANTIC
STATES INTO FRIDAY AS WEAK WAVES OF LOW PRESSURE RIDE ALONG IT.
HIGH PRESSURE IS EXPECTED TO SETUP ANCHOR ACROSS THE REGION ON
SATURDAY AND SUNDAY. THIS AREA OF HIGH PRESSURE WILL BE SANDWICHED
BETWEEN AN AREA OF LOW PRESSURE MOVING OFFSHORE OF THE MID-
ATLANTIC ON SATURDAY AND ANOTHER AREA OF LOW PRESSURE APPROACHING
LAKE SUPERIOR ON SUNDAY.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
A COLD FRONTAL BOUNDARY WILL CONTINUE MOVING SOUTHEAST
THROUGH THE REGION TONIGHT WITH MID-LEVEL CLOUDS GRADUALLY CLEARING
OUT. IT WILL BE A CLEAR CRISP NIGHT WITH FAVORABLE CONDITIONS FOR
RADIATIONAL COOLING. WENT A TOUCH COOLER THAN THE MAV/MET ON LOWS
TONIGHT DUE TO THE RADIATIONAL COOLING AS NORTHWEST WINDS BECOME
LIGHT TONIGHT. THE NEXT SIX TO TWELVE HOURS ALSO INCORPORATE
ELEMENTS OF THE LAV WHICH APPEARS TO HAVE A GOOD HANDLE ON THE
CURRENT SETUP.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
HIGH PRESSURE WILL MOVE THROUGH THE REGION ON MONDAY. CLOUDS
WILL INCREASE SOME INT HE AFTERNOON FROM SOUTH TO NORTH. MODEL CONSENSUS
SUGGESTS A LOW CHANCE FOR RAIN SHOWERS LATE IN THE DAY ACROSS THE
SOUTHERN DELMARVA AND USED THE 09Z SREF FOR SOME VERY LIGHT QPF.
GIVEN THE LAST FEW DAYS HAVE ENDED UP COOLER THAN THE MAV AND
PARTICULARLY THE MET THE LAST FEW DAYS, FORECASTED HIGH TEMPERATURES
ARE AT OR JUST BELOW THE MET. LIGHT AND VARIABLE WINDS SHOULD COME
AROUND TO THE SOUTHWEST IN THE AFTERNOON UNDER 10 MPH.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
THE NEW WRF-NMMB INITIALIZATION WAS SLIGHTLY BETTER THAN THE GFS.
OVERALL THERE IS SOMEWHAT BETTER MODEL CONSENSUS OVER EASTERN
NOAM TODAY THAN THERE WAS YESTERDAY, ESPECIALLY WITH THE FIRST
SYSTEM PASSING TO OUR SOUTH. A BLOCKY WEATHER PATTERN IS EXPECTED
TO PERSIST. THIS WILL PREVENT THE HEAT RIDGE FROM MAKING IT THIS
FAR NORTH. REGARDLESS, FOR MOST OF THE LONG TERM THERE IS A RETURN
OF MORE TYPICAL WARMER AND MORE HUMID (SOUTH ESPECIALLY) AUGUST
WEATHER IN OUR CWA WITH THE LIKELIEST DAY FOR SHOWERS AND
THUNDERSTORMS ON THURSDAY.

AT THE END OF THE LONG TERM MODELS CONTINUE TO STRUGGLE WITH THE
EVOLUTION OF THE MID-LEVEL FLOW OVER THE NORTHEAST CONUS AND
ATLANTIC CANADA DURING THE D+6 AND D+7 TIMEFRAME. THIS IS LARGELY
ATTRIBUTED TO MODEL DIFFERENCES IN THE HANDLING OF SHORTWAVE
ENERGY CURRENTLY OVER THE ALEUTIAN ISLANDS. THE MID-LEVEL HEIGHT
FIELD WILL EVOLVE INTO A TROUGH IN THE WEST AND SUBSEQUENT RIDGING
IN THE EAST...BUT THIS WILL BE COMPLICATED BY PERSISTENT BLOCKING
/POSITIVE HEIGHT ANOMALIES/ INVOF THE DAVIS STRAIGHT...LEADING TO
A REX-BLOCK OVER THE NORTHEAST CONUS AND ATLANTIC CANADA. THE
12Z/17 EURO/GFS ARE IN BETTER AGREEMENT TODAY WITH THE POSITION OF
THE REX BLOCK AT 00Z SUNDAY...INDICATING A CLOSED HIGH OVER QUEBEC
AND A CLOSED LOW SOUTH OF NOVA SCOTIA AT 500 HPA. ALTHOUGH BOTH
THE EURO AND GFS OPERATIONAL RUNS ARE IN GENERAL AGREEMENT WITH
THEIR RESPECTIVE ENSEMBLE MEANS...THERE IS CONSIDERABLE SPREAD
AMONGST THE INDIVIDUAL MEMBERS WITH REGARD TO THE MID-LEVEL HEIGHT
FIELDS...WHICH TRANSLATES INTO UNCERTAINTY WITH RESPECT TO THE
POSITION OF SURFACE FEATURES. MORE IMPORTANTLY... THE MODELS HAVE
SHOWN LITTLE RUN-TO-RUN CONSISTENCY AT THIS POINT... ESPECIALLY
GIVEN THE TIME RANGE AND THE PLACEMENT OF THE MAIN SHORT-WAVE
ENERGY WHICH IS STILL OVER THE DATA-SPARSE PACIFIC OCEAN.

THE GFS. WRF AND CAN GGEM ALL TRENDED TOWARD THE ECMWF AND UKMET
FOR MONDAY NIGHT. THE DP/DT ON THE TRIGGERING CLOSED LOW CONTINUES
TO BE SLIGHTLY FASTER AND SLIGHTLY MORE SOUTHEAST WHICH
CORROBORATE THE EUROPEAN MODEL EVOLUTION. THUS THE TREND STARTED
BY THE MID SHIFT WAS CONTINUED AS WE SHAVED POPS DOWNWARD EXCEPT
FOR DELMARVA. WE ALSO EDGED SOUTHWARD THE MENTION OF HEAVY RAIN
AND THUNDER. OUR THINKING IS CLOSEST TO THE HI RES ARW SOLUTION.
IT NOW APPEARS MORE LIKELY TO BE SOUTH OF WHERE THE HEAVIEST RAIN
FELL LAST WEEK. MIN TEMPERATURES WERE CLOSE TO STAT GUIDANCE NORTH
WHERE CLOUD COVERAGE IS NOT AS CONFIDENT AND HIGHER THAN STAT
GUIDANCE SOUTH BECAUSE OF CLOUDS.

A FASTER EXIT TO PCPN CHANCES IS FORECAST FOR TUESDAY MORNING. IN
THE WAKE OF THE DEPARTING LOW PRESSURE SYSTEM, THE GENERAL
SYNOPTIC SCALE FLOW REMAINS ONSHORE. NORTH OF ABOUT 40NISH THE
ONSHORE FLOW IS PREDICTED TO BE RELATIVELY DRY. SOUTH OF THERE THE
ONSHORE FLOW SHOULD BE MORE PROBLEMATICAL AND WE ARE CLOUDIER.
GFS MLCAPE FORECAST WAS CONTAMINATED BY MDL SFC DEW POINTS 5 TO
8F HIGHER THAN ITS STATISTICAL MOS. WITH NO OTHER MODEL
CORROBORATION WE ARE EXPECTING ANY UPSLOPE OR DAYTIME HEATING
CONVECTION TO REMAIN WEST OF OUR CWA THE REST OF TUESDAY. WE WENT
ABOVE STAT GUIDANCE NORTHWEST BECAUSE OF MORE SUNSHINE, NEAR
CENTRAL AND BELOW SOUTHEAST BECAUSE OF ONSHORE FLOW.

ON TUESDAY NIGHT SOME RESIDUAL SHOWERS MIGHT MAKE IT INTO OUR CWA
AND WE KEPT LOW POPS WEST. GIVEN THE TREND TOWARD A FASTER
RESOLUTION AND THAT THE KICKER CLOSED LOW INITIALIZED OVER
SASKATCHEWAN IS ALSO TRENDING FASTER, WE HAVE UPPED POPS FOR
WEDNESDAY AND EXTENDED THEM FARTHER TO THE EAST. THERE IS STILL A
NOSE OF STABILITY OVER OUR CWA FROM A WAKE HIGH IN NEW ENGLAND.
SO, IT LOOKS AS THOUGH CONVECTION IS NOT HOME GROWN, BUT MOVES
EASTWARD. EITHER WAY, THERE ARE ENOUGH SHORT WAVES UPWIND TO
BELIEVE SOME ARE FOR REAL. THE AIR MASS ITSELF IS PREDICTED TO BE
SLIGHTLY WARMER AND WE UPPED MAX TEMPS EVER SO SLIGHTLY.

THURSDAY RIGHT NOW LOOKS TO BE THE DAY WITH THE MOST WIDESPREAD
CONVECTIVE ACTIVITY WITH HEAVY RAIN MORE OF A CONCERN THAN SEVERE AT
THIS POINT. PREDICTED PWATS SHOULD GET ABOVE 1.50 INCHES AND RIGHT
NOW THE MID LEVEL LAPSE RATES AND 0-6KM BULK SHEAR VALUES NOT THAT
FOREBODING. OF COURSE, IF SOLUTIONS KEEP ON ADVANCING IN TIME,
THE GO TO PERIOD MIGHT BE WEDNESDAY NIGHT. WITH TROFINESS
LINGERING, WE KEPT IN A CHANCE FOR INSTABILITY SHOWERS AND
THUNDERSTORMS FOR FRIDAY.

ON THE WEEKEND...A GENERAL AREA OF LOW PRESSURE IS EXPECTED TO BE
INVOF THE MID-ATLANTIC COAST ON SATURDAY...GRADUALLY MOVING
OFFSHORE...AS A RIDGE OF HIGH PRESSURE NOSES IN FROM THE
NORTHEAST. ALTHOUGH THIS WOULD IMPLY A DRYING TREND ON
SATURDAY...THE REGION WILL STILL BE UNDER THE INFLUENCE OF A
CYCLONIC FLOW ALOFT AS WELL AS AN ONSHORE FLOW...SO KEPT A CHANCE
OF SHOWERS IN THE FORECAST. THE MODELS MAY BE TO PROGRESSIVE
BUILDING A MID-LEVEL RIDGE INTO THE REGION ON SUNDAY GIVEN THEIR
TYPICAL BIAS OF BREAKING DOWN /REX/ BLOCKS TOO QUICKLY.
THEREFORE...KEPT A SLIGHT CHANCE OF SHOWERS IN THE FORECAST.
OVERALL...EXPECT TEMPERATURES SLIGHTLY BELOW NORMAL.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

A COLD FRONT WITH SOME ASSOCIATED MID-LEVEL VFR CEILINGS IS MOVING
SOUTHEAST ACROSS THE REGION. WINDS HAVE INCREASED SLIGHTLY THIS
AFTERNOON WITH A FAVORABLE SET-UP FOR SOME WIND GUSTS CLOSE TO 20
KT FOR THE MID AND PERHAPS LATE AFTERNOON HOURS FROM THE
NORTHWEST.

WINDS WILL RELAX BY THIS EVENING AND CLOUDS WILL CONTINUE TO CLEAR
OUT. NO FOG OR LOW VISIBILITIES ARE EXPECTED TONIGHT. VFR TONIGHT.
SOME MID-LEVEL CLOUDS MAY ENTER THE PICTURE TOMORROW AFTERNOON,
BUT STILL VFR WITH WEST-SOUTHWEST WINDS UNDER 10 KTS AFTER
STARTING THE DAY LIGHT AND VARIABLE.

OUTLOOK...
MONDAY NIGHT AND TUESDAY...LOPRES TRACKS SOUTH OF THE AREA. BEST
CHANCE FOR SHRA AND POSSIBLY TSRA SHOULD BE FOR AIRPORTS SOUTH OF
THE TERMINALS. A PERIOD OF MVFR OR IFR CONDITIONS POSSIBLE AT
TIMES OF HEAVIER SHRA AND ALSO AT AIRPORTS/TERMINALS NEAR THE
COAST WITH ONSHORE FLOW. VFR (OR REMAINING VFR) MOST AREAS BY
TUESDAY AFTN.

TUESDAY NIGHT AND WEDNESDAY MORNING...PREDOMINATELY VFR.

WEDNESDAY AFTERNOON THROUGH FRIDAY...SCT SHRA/TSRA AS MULTIPLE
DISTURBANCES TRACK THRU THE REGION. SOME FLIGHT RESTRICTIONS LIKELY,
ESPECIALLY CENTERED AROUND THURSDAY.

&&

.MARINE...
SEAS WILL BE FROM 2 TO 3 FEET IN THIS PERIOD. NORTHWEST WINDS WILL
DIMINISH OVERNIGHT BECOMING VARIABLE. A SOUTHERLY WIND UNDER 10
KNOTS WILL DEVELOP IN THE AFTERNOON.

OUTLOOK...
MONDAY NIGHT THROUGH TUESDAY...SMALL CRAFT ADVISORY CONDITIONS
CHANCES ARE LOOKING SLIGHTLY LESS AS THE LOW PRESSURE SYSTEM AND
ONSHORE FLOW HAVE TRENDED WEAKER. STILL LOWEST CONFIDENCE ON
SOUTHERN OCEANIC WATERS.

TUESDAY NIGHT THROUGH FRIDAY...ONSHORE FLOW CONTINUES BUT WILL
WEAKEN AND GENERALLY REMAIN WEAK OVER TIME. GREATEST MARINE
CONCERN LOCALIZED STRONGER WINDS AND SEAS IN THUNDERSTORMS,
CENTERED ON THURSDAY.

&&

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

&&

$$
SYNOPSIS...GIGI/KLEIN
NEAR TERM...GAINES
SHORT TERM...GAINES
LONG TERM...FRANCK/GIGI
AVIATION...GAINES/GIGI/KLEIN/O`HARA
MARINE...GAINES/GIGI/KLEIN/O`HARA






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