Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 250150
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
950 PM EDT MON AUG 24 2015

.SYNOPSIS...
A COLD FRONT OVER CENTRAL PENNSYLVANIA WILL MOVE INTO OUR
AREA LATE TONIGHT AND OFF THE COAST ON TUESDAY. A HIGH PRESSURE
SYSTEM FROM THE NORTHERN PLAINS IS EXPECTED TO REACH THE
FORECAST AREA ON FRIDAY AND MOVE OFFSHORE ON SATURDAY.
THE HIGH PRESSURE SYSTEM IS THEN PREDICTED TO REMAIN NEARLY
STATIONARY OFF THE EASTERN SEABOARD ON SUNDAY AND MONDAY.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
AS OF 9 PM EDT...THE COLD FRONT WAS JUST ENTERING WESTERN SECTIONS
OF THE REGION. THUNDERSTORMS, ALTHOUGH LIMITED IN COVERAGE, HAVE
BEEN STRONGER THAN PREVIOUSLY ANTICIPATED, ESPECIALLY IN THE
DELMARVA REGION. IT LOOKS LIKE THE INSTABILITY JUST AHEAD OF THE
FRONT WAS POORLY MODELED, WITH THE 00Z KIAD SOUNDING SHOWING
AROUND 1500 J/KG OF MOST UNSTABLE CAPE. STILL, WITH LIMITED
COVERAGE, AND A SLIGHTLY FASTER ARRIVAL OF THE FRONT, IT LOOKS
LIKE MOST AREAS WILL REMAIN DRY. SO DECREASED POPS FOR MOST
LOCATIONS EXCEPT DELMARVA.

WITH REGARDS TO TEMPERATURES AND WINDS, ANOTHER MILD NIGHT IS IN
STORE OVERALL AS MOST OF THE REGION WILL CONTINUE WITH A SOUTH TO
SOUTHWEST WIND IN ADVANCE OF THE FRONT, BEFORE SHIFTING TO A
WESTERLY DIRECTION DURING THE OVERNIGHT TO EARLY MORNING HOURS
TUESDAY. OUR NORTHWEST ZONES WILL BEGIN TO FEEL THE COOLER/DRIER AIR
ADVANCING INTO THE REGION AS MINIMUM TEMPS SHOULD BOTTOM OUT IN THE
LOWER 60S. ELSEWHERE, LOW TEMPERATURES MAINLY IN THE UPPER/MID 60S
ARE ANTICIPATED.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
THE PREVIOUSLY MENTIONED COLD FRONT WILL BE SLOWING AS IT TRIES TO
EXIT THE COAST DURING THE DAYTIME TUESDAY. WITH THIS BOUNDARY
LINGERING ACROSS OUR FAR EASTERN AREAS TO JUST OFFSHORE, SOME
SCATTERED SHOWERS MAY HANG AROUND THROUGH THE MORNING HOURS,
ESPECIALLY FOR LOCATIONS NEAR THE COAST. THEREAFTER, ANY REMAINING
SHOWER ACTIVITY SHOULD BE PASSING OFFSHORE. OTHERWISE, FOR THE
REMAINDER OF THE FORECAST AREA, A BROAD AREA OF HIGH PRESSURE TO OUR
WEST, STRETCHING ACROSS THE PLAINS TO MIDWEST, WILL BEGIN TO BUILD
EAST TOWARD OUR REGION. THIS WILL ALLOW FOR CLEARING SKIES THROUGH
THE DAY, ACCOMPANIED BY WESTERLY WINDS BRINGING IN A DRIER AIRMASS.
MODELED DEWPOINTS ARE SHOWN TO BE DROPPING INTO THE 50S FOR MUCH OF
THE REGION BY THE AFTERNOON. FOR TEMPERATURES, WE PRIMARILY TOOK A
MET/MAV GUIDANCE BLEND, AND WE ANTICIPATE HIGHS TO BE MAINLY IN THE
80S ACROSS THE REGION.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
THE 500MB INITIALIZATION HAS CONTINUED A RECENT TREND IN WHICH THE
GFS LOOKS BETTER IN WRN NOAM WHILE THE WRF/NAM AND GFS LOOK EQUALLY
AS GOOD FARTHER EAST ACROSS THE CENTRAL AND ERN CONUS AS WELL AS
SOUTHERN CANADA. AT 850MB AND 925MB THE WRF/NAM INITIALIZATION WAS
CLOSER THAN THE GFS. DP/DTING THE GFS INITIALIZATION, THE LEANING
IS TOWARD A HIGHER AMPLITUDE PATTERN. DP/DTING THE GFS OVER THE
UPCOMING WEEKEND, THERE IS NO RUN TO RUN CONTINUITY WITH THE SHORT
WAVES AND PCPN.

OVERALL A QUIET PERIOD AS AN ANOMALOUSLY DEEP TROF OVER THE EASTERN
CONUS AT THE START OF THE LONG TERM LIFTS INTO NORTHEASTERN CANADA
AND GETS REPLACED BY A MORE RIDGE DOMINATED PATTERN OVER THE CONUS.
COOLER THAN NORMAL WEATHER (ESPECIALLY MIN TEMPS) AT THE START OF
THE LONG TERM WILL SLOWLY BE TEMPERED AND BECOME WARMER THAN NORMAL
BY THE END OF OUR DETERMINISTIC FORECASTS.

BY MID TUESDAY EVENING ALL OF THE MODELS HAVE THE FRONT SUFFICIENTLY
OFFSHORE TO KEEP THE DRY FORECAST GOING. DRIER AIR WILL BE FILTERING
IN BEHIND THE FRONT AND WITH THE PREDICTED GRADIENT WEAK ENOUGH FOR
DECOUPLING SHOULD BE A RELATIVELY COOL NIGHT IN SUBURBAN AND RURAL
AREAS. STAT GUIDANCE HAS A REASONABLE TAKE ON THIS AND WE WENT PRETTY
MUCH IN LINE.

ON WEDNESDAY, THE DOMESTIC MODELS ARE KEYING ON OPPOSITE ENDS OF
OUR CWA WITH LOW PCPN CHANCES, WITH THE GFS IN SUSSEX COUNTY DE AND
THE NAM MUCH CLOSER TO SUSSEX COUNTY NEW JERSEY. DONT KNOW IF THE
DP/DT TREND WITH THE GFS HAS BEEN CARRIED TOO FAR, BUT MOST OTHER 12Z
MODELS ARE MORE PROGRESSIVE WITH THE TROF THAN THE GFS. ALSO THE
GEFS MEAN IS FASTER. THIS REMOVES SUSSEX COUNTY DE FROM THE
EQUATION. AT THE GEOGRAPHICAL OTHER END OF THE SPECTRUM, THE NAM
BRINGS SHOWERS INTO THE NWRN PART OF OUR CWA. WHILE OTHER MODELS DO
NOT IN SPITE OF DECENT PVA. THE LATTER PROBABLY BECAUSE PREDICTED MSTR
IS LAGGING, BUT ALWAYS LIKED THE LOOK OF PVA VS MSTR AS A BETTER
PREDICTOR AT THIS FORECAST TIME RANGE. WE ARE GOING TO KEEP IN THE
LOW CHANCE POPS. PATTERN HAS A VERY AUTUMNAL LOOK TO IT FOR OUR
NWRN CWA. BOTH MODELS PREDICTED THERMAL FIELDS SUPPORT HIGHER
GFS MOS FOR MAX TEMPS.

SIMILAR SCENARIO FOR WEDNESDAY NIGHT WHERE THE GRADIENT LOOKS LOOSE
ENOUGH FOR DECOUPLING AND ANOTHER PLEASANT NIGHT, ESPECIALLY OUTLYING
AREAS. WE DO NOT BELIEVE THE DAYTIME CU SHOULD BE TRAPPED UNDER THE
INVERSION, BUT THAT IS ONE SCENARIO THAT MIGHT MAKE OUR MIN TEMPS
TOO LOW.

THE LAST OF THE SHORT WAVES BEFORE THE TROF FLATTENS IS PREDICTED TO
COME THROUGH ON THURSDAY. HERE WE GET TOO FAR OUT IN TIME TO HAVE
CONFIDENCE IN THE SHORT WAVE PLACEMENT. WE ARE DEFERRING TO
CONSENSUS AND MODEL QPF. WHILE WE WILL SHOW A DIURNAL INCREASE IN
SKY COVER, WE WILL GO POPLESS. PREDICTED THERMAL FIELDS SUGGEST
A 2-3F BUMP DOWN IN MAX TEMPS WHICH WE FOLLOWED.

THE THERMAL TROF AND THE END OF THE COOLER NIGHTS WILL OCCUR ON
THURSDAY NIGHT. THE AIR MASS MODIFICATION WILL START ON FRIDAY.
BECAUSE OF THE RELATIVELY CHILLY START, HIGHS ARE NEARLY THE
SAME AS THURSDAY.

OVER THE WEEKEND A NON GFS MODELING CONSENSUS HAS A CENTRAL
CONUS WEAK TROF SHEARING OUT AND A COLD FRONT FROM EASTERN CANADA
DISSIPATING BEFORE REACHING OUR CWA. AS THE PREVIOUS SHIFT
MENTIONED, WHILE THERE IS A CHANCE (VS NO CHANCE ON FRIDAY)FOR PCPN
NEITHER 12Z MODEL CONSENSUS SCENARIO SUPPORTS A HIGH ENOUGH
CONFIDENCE TO INCLUDE A CHANCE. WE ARE MUCH MORE CONFIDENT THAT THE
UPWARD TREND IN TEMPERATURES WILL CONTINUE OVER THE WEEKEND
AND INTO MONDAY.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

FOR THE 00Z TAFS...EXPECT MOSTLY VFR CONDITIONS, UNLESS A TAF SITE
IS DIRECTLY IMPACTED BY A SHRA OR THUNDERSTORM, IN WHICH CASE MVFR
OR EVEN BRIEF IFR CONDITIONS ARE POSSIBLE. AT THIS POINT THOUGH,
COVERAGE IS QUITE LIMITED, SO IT IS QUITE UNCERTAIN AS TO IF ANY
TAF SITE WILL BE AFFECTED.

SEVERAL MODELS CONTINUE TO SHOW A POTENTIAL FOR LOW CLOUDS AND BR
BETWEEN 06 AND 15Z FOR MANY TAF SITES. HOWEVER, IT LOOKS LIKE THE
COLD FRONT, AND THUS DRIER AIR, WILL BE SLIGHTLY FASTER THAN
PREVIOUSLY EXPECTED. PLUS, THE TREND OVER THE LAST SEVERAL NIGHTS
HAS BEEN FOR THE CONDITIONS TO BE DRIER THAN EXPECTED. SO HAVE
LEFT THIS OUT OF THE TAFS FOR NOW. OTHERWISE, EXPECT VFR
CONDITIONS THROUGH THE DAY TOMORROW.

OUTLOOK...
TUESDAY NIGHT THROUGH SATURDAY...PREDOMINATELY VFR CONDITIONS.
EVERY LATE NIGHT/EARLY MORNING SOME LOW CLOUDS AND FOG ARE
POSSIBLE AT MORE RURAL AIRPORTS, ESPECIALLY IF LOCATED IN VALLEYS
OR NEAR CREEKS OR RIVERS.

&&

.MARINE...
WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY
LEVELS THROUGH TONIGHT AND TUESDAY. A GENERAL SOUTHERLY FLOW WILL
CONTINUE THROUGH MOST OF TONIGHT IN ADVANCE OF A COLD FRONT,
FOLLOWED BY A WIND SHIFT TO THE SOUTHWEST/WEST FOR THE WATERS ONCE
THE FRONT NEARS AND SLOWLY PASSES BY TO THE EAST LATER ON TUESDAY.
THERE COULD BE SOME WIND GUSTS AT TIMES TO AROUND 20 KNOTS. IN
ADDITION, SEAS FOR THE COASTAL WATERS WILL AVERAGE IN THE 3 TO 4
FOOT RANGE. ISOLATED THUNDERSTORMS ARE POSSIBLE LATE TONIGHT AND
INTO TUESDAY AS THE COLD FRONT NEARS AND PASSES OFFSHORE. GUSTY
WINDS WILL BE POSSIBLE WITH THESE STORMS.

OUTLOOK...
TUESDAY NIGHT THROUGH SATURDAY...NO MARINE HEADLINES
ARE ANTICIPATED AS A BUILDING HIGH PRESSURE SYSTEM REACHES AND
THEN REMAINS NEAR OUR COASTAL WATERS.

&&

.TIDES/COASTAL FLOODING...
TIDES ALONG THE CHESAPEAKE BAY WILL BE HIGHER THAN NORMAL FOR THE
HIGH TIDE TUESDAY MORNING. HOWEVER, AT THIS TIME, GUIDANCE SHOWS
THE HIGH TIDE JUST BELOW MINOR FLOODING THRESHOLDS AND AT
CAMBRIDGE, OBSERVATIONS ARE RUNNING SLIGHTLY BELOW GUIDANCE
CURRENTLY. SO DO NOT PLAN ON ANY COASTAL FLOOD WARNING FOR THE
CHESAPEAKE NORTH EASTERN SHORE AT THIS TIME, BUT WILL CONTINUE TO
WATCH CLOSELY.

&&

.RIP CURRENTS...
THERE IS A MODERATE RISK FOR THE FORMATION OF DANGEROUS RIP
CURRENTS ALONG THE NEW JERSEY SHORE ON TUESDAY.

&&

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

&&

$$
SYNOPSIS...DRAG/GIGI
NEAR TERM...JOHNSON/KLINE
SHORT TERM...KLINE
LONG TERM...GIGI
AVIATION...DRAG/GIGI/JOHNSON
MARINE...DRAG/GIGI/KLINE
TIDES/COASTAL FLOODING...
RIP CURRENTS...



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