Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 271028
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
628 AM EDT MON JUL 27 2015

.SYNOPSIS...
A WEAKENING COLD FRONT IS EXPECTED TO DISSIPATE TODAY OVER OUR
AREA. A HIGH PRESSURE SYSTEM WILL THEN BUILD BACK OVER THE MID
ATLANTIC STATES FOR THE MIDDLE OF THE WEEK. ANOTHER COLD FRONT
SHOULD MOVE THROUGH THE REGION THURSDAY NIGHT, THEN WEAK HIGH
PRESSURE BUILDS INTO THE NORTHEAST LATER FRIDAY INTO THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE SYNOPTIC SETUP IS COMPRISED OF NORTHWEST FLOW ALOFT WITH AN
EMBEDDED SHORT WAVE TROUGH. THIS FEATURE WILL CROSS OUR AREA DURING
THE COURSE OF TODAY. THE AREA OF CONVECTION AIDED BY ENOUGH
INSTABILITY COMBINED WITH SOME LIFT AND COLD POOL GENERATION
CONTINUES TO GRADUALLY WEAKEN AS IT REACHES THE COAST AND THE
ADJACENT COASTAL WATERS. IT APPEARS THAT THERE WILL BE A LULL FOR
A TIME BEFORE AT LEAST ISOLATED TO SCATTERED CONVECTION REDEVELOPS
WITH RENEWED HEATING WITHIN A MOIST BOUNDARY LAYER. THE POPS WERE
ADJUSTED BASED ON THE LATEST RADAR TRENDS, THEN BLENDED INTO
CONTINUITY.

THE PW VALUES ARE AROUND 1.5 INCHES, AND THIS COMBINED WITH
ANY CLUSTERING OF THE CONVECTIVE UPDRAFTS WILL LEAD TO HEAVY
RAINFALL AND POOR DRAINAGE FLOODING IN LOCALIZED AREAS. IT DOES
NOT APPEAR A LOT OF LIFT IS NEEDED WITHIN THIS AIRMASS TO PROMOTE
NEW DEVELOPMENT, ALTHOUGH A WEAKENING COLD FRONT GENERALLY
DISSIPATES INTO OUR AREA. A WEAK SURFACE TROUGH MAY PERSIST THOUGH
AND HELP FOCUS SOME NEW DEVELOPMENT THROUGH THE DAY, WHICH MAY BE
CENTERED ON THE INTERSTATE 95 CORRIDOR AND ALSO PERHAPS TERRAIN
ENHANCED.

AS FOR THE HIGH TEMPERATURES, WE MOSTLY WENT WITH A NAM/GFS MOS
BLEND WITH THE ANTICIPATION OF ENOUGH CLOUDS AND CONVECTION AROUND.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
THE SHORT WAVE TROUGH IS FORECAST TO SHIFT TO OUR EAST THIS EVENING,
AND THEN SOME SUBTLE HEIGHT RISES OCCUR AS SLIGHT RIDGING STARTS TO
ARRIVE FROM THE WEST. AS A RESULT, THE PVA WITHIN THE NORTHWESTERLY
FLOW ALOFT IS FORECAST TO WANE AND THIS SHOULD ALLOW ANY CONVECTION
TO DISSIPATE BY LATE EVENING FOR MUCH OF THE AREA. THEREFORE, WE
TRENDED THE POPS DOWNWARD THROUGH THE EVENING WITH THE LAST
MENTIONABLE CONVECTION IN PORTIONS OF THE DELMARVA OVERNIGHT.
OTHERWISE, SOME PARTIAL CLEARING SHOULD TAKE PLACE FROM THE
NORTHWEST ALTHOUGH SOME HIGH LEVEL CLOUDS MAY CONTINUE TO MOVE
ACROSS.

THE PRESENCE OF LIGHT WINDS AND AREAS OF LESSENING CLOUD COVER MAY
RESULT IN LOCAL FOG DEVELOPMENT OVERNIGHT, ESPECIALLY IN AREAS WHERE
HEAVY RAIN HAS FALLEN WHICH WILL ASSIST IN LOW-LEVEL MOISTURE
POOLING. THIS MAY BE LOCALIZED ENOUGH THEREFORE IT WAS NOT INCLUDED
ATTM. AS FOR THE LOW TEMPERATURES, WE SIDED WITH A GFS/NAM MOS BLEND
WITH SOME MINOR LOCAL TWEAKS.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
THE MODEL TENDENCY OF THE LAST COUPLE OF DAYS HAS CONTINUED TONIGHT
WITH THE GFS HAVING A BETTER 500MB INITIALIZATION AND THE WRF-
NMMB A BETTER 850MB AND 925MB INITIALIZATION AS THE GFS WAS TOO
WARM WITH ITS ERRORS. THIS INCLUDED THE NORTHERN PLAINS. MOVING
FORWARD TO THE ACTUAL MODEL THERMAL RUN, THE GFS IS MORE IN LINE
WITH THE SREF AND THE ECMWF THAN THE OP WRF-NMMB WHICH IS ON THE
HOT SIDE. NOT SURPRISING THAT THE DP/DT ON THE GFS IS SLOWER WITH
THE CFP PASSAGE THURSDAY.

BECAUSE OF THE ONGOING HEAVY RAIN IN OUR CWA, THE LONG TERM WAS
HEAVILY WEIGHTED TOWARD A CONTINUITY AND WPC BLEND. HEAT RELATED
HEADLINES REMAIN A POSSIBILITY FOR WEDNESDAY AND THURSDAY ESPECIALLY
IN URBAN AREAS. THERE IS STILL SOME UNCERTAINTY AS TO WHETHER ONE
OR TWO DAYS WILL MEET THE CRITERIA, SO WE CONTINUED MENTION IN THE
HWO, BUT DID NOT ISSUE A WATCH.

ON TUESDAY, A MID LEVEL CAP IS PREDICTED TO DEVELOP ACROSS MOST OF
OUR CWA. THE LATEST AND WEAKEST ARRIVAL IS IN THE SOUTHERN PART
OF OUR CWA WHERE WE KEPT A LOW CHANCE OF AFTERNOON THUNDERSTORMS.
THE GFS HAS HAD DECENT RUN TO RUN CONTINUITY IMPLYING THAT BAY
BREEZES MAY BE THE THUNDERSTORM TRIGGER.

IRONICALLY, BECAUSE OF A DEVELOPING OFFSHORE LOW, COOLER AIR WRAPS
BACK TOWARD THE DELMARVA AND SOUTHERN NEW JERSEY COAST. THIS IS
ALL RELATIVE BECAUSE THE AIR MASS IS STILL SUMMER TIME WARM. BUT,
THE TOPSY-TURVEY THERMAL PICTURE CONTINUES AS SUSSEX COUNTY NEW
JERSEY MAY HAVE HIGHER TEMPS THAN SUSSEX COUNTY DELAWARE. 10C ADDED
TO PREDICTED 925 TEMPS HAVE WORKED THE BEST THE LAST COUPLE OF DAYS
FOR MAX TEMPS AND WAS USED AGAIN. STAT GUIDANCE WAS PRETTY CLOSE
ALSO. THE WINDS ARE NOT EXPECTED TO BE THAT STRONG, BUT THERE IS
DRY AIR ALOFT AND DEW POINTS SHOULD DROP A BIT, ESPECIALLY THE
NORTHWEST TWO THIRDS OF OUR CWA.

FROM TUESDAY NIGHT THROUGH WEDNESDAY NIGHT, THE SURFACE HIGH
PRESSURE SYSTEM WILL BE MORE IN CONTROL AND NO PRECIPITATION IS
FORECAST. WEDNESDAY WILL BE HOTTER WITH NEARLY ALL OF OUR CWA
REACHING INTO THE LOWER AND MID 90S. THE STICKING POINT FOR
REACHING HEAT HEADLINE CRITERIA MAY BE THE DEW POINTS. DISGUSTING
MID 70S OR HIGHER DEW POINTS ARE STILL GEOGRAPHICALLY PRETTY FAR
REMOVED FROM OUR AREA AND WITH THE HIGH PRESSURE SYSTEM IN
PLACE OVER US, NOT MUCH OF AN ADVECTION FACTOR INVOLVED YET.
THERMALLY WE ARE STILL JUXTAPOSITIONED, PRETTY UNIFORM
(EXCEPT FOR ELEVATION AND SHORE POINTS) IN MAX TEMPS. A VERY WARM
WEDNESDAY NIGHT EXPECTED.

GFS HAS BACKED AWAY FROM A FASTER COLD FRONTAL PASSAGE TIMING AND
NEVER CONFIDENT ABOUT A COLD FRONT SAVING THE DAY FROM THE HEAT
IN SUMMER. THE ECMWF FROM A FEW DAYS AGO HAS WENT THE GFS`S WAY
THERMALLY ALTHOUGH ITS STAT GUIDANCE REMAINS STRANGELY LOW WITH
MAINLY LOWER 90S FOR HIGHS. NCEP GUIDANCE CONTINUES TO POINT TO
THIS DAY AS THE MOST LIKELY TO REACH HEAT HEADLINES. WITH AN
APPROACHING COLD FRONT TO POOL DEW POINTS AND A STRONGER SOUTHWEST
FLOW TO ADVECT THOSE NASTY DEW POINTS IN, THIS APPEARS LOGICAL.
MODELS NOT TERRIBLY ENTHUSED ABOUT THUNDER, SHOWING THE ENERGY
SPLIT. WE KEPT THE CONTINUITY GOING WITH LEAVING POPS AS CHANCE.

NOT MANY CHANGES TO THE REST OF THE LONG TERM. THE COLD FRONTAL
PASSAGE SHOULD BRING ONLY SLIGHTLY COOLER, MORE IMPORTANTLY, DRIER
AIR INTO OUR CWA ON FRIDAY AND SATURDAY. SOME MAX TEMPS SHOULD
STILL REACH 90, BUT THE HEAT INDEX AND MAX TEMPS WILL BE CLOSER TO
ONE AND THE SAME. AN APPROACHING COLD FRONT FOR SUNDAY BRINGS
PRECIPITATION CHANCES BACK THROUGHOUT OUR CWA.

&&

.AVIATION /10Z MONDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

TODAY...SHOWERS AND SOME THUNDERSTORMS CLEARING KMIV AND KACY
EARLY, THEN THERE SHOULD BE A LULL UNTIL MOSTLY FROM MIDDAY ON
WHEN ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS REDEVELOP.
SOME MVFR CLOUD BASES AROUND EARLY, ALTHOUGH THIS APPEARS TO BE ON
THE LOCALIZED SIDE. OTHERWISE, VFR IS ANTICIPATED /LOCAL LIGHT
FOG POSSIBLE EARLY THIS MORNING/. WE CARRIED A TEMPO GROUP FOR
SHOWERS THIS AFTERNOON AS THERE IS LOWER CONFIDENCE WITH THUNDERSTORM
PLACEMENT. SOUTH-SOUTHWEST WINDS GENERALLY 5-10 KNOTS.

TONIGHT...SOME SHOWERS AND THUNDERSTORMS WITH BRIEFLY REDUCED
VISIBILITIES AND/OR CEILINGS IN THE EVENING ARE EXPECTED TO
DIMINISH. THERE IS THE CHANCE FOR LOCAL FOG TO DEVELOP LATE.
SOUTHERLY WINDS 5 KNOTS OR LESS.

OUTLOOK...
TUESDAY...MAINLY VFR. ISOLATED AFTN THUNDERSTORMS POSSIBLE SOUTH.

TUESDAY NIGHT THROUGH WEDNESDAY...VFR CONDITIONS EXPECTED.

WEDNESDAY NIGHT...SOME MVFR CONDITIONS DUE TO VSBY RESTRICTIONS
POSSIBLE AT MORE RURAL AIRPORTS AND TERMINALS.

THURSDAY AND THURSDAY NIGHT...VFR. BUT POCKETS OF MVFR TO IFR
CONDITIONS AS SCATTERED SHOWERS AND THUNDERSTORMS MOVE THROUGH.

FRIDAY...SOME PATCHY RESTRICTIVE FOG EARLY, OTHERWISE VFR.

&&

.MARINE...
THE CONDITIONS ARE ANTICIPATED TO REMAIN BELOW SMALL CRAFT ADVISORY
CRITERIA TODAY AND TONIGHT. A SOUTHERLY FLOW IS EXPECTED TO CONTINUE
AS A DISSIPATING COLD FRONT ARRIVES TODAY. SOME GUSTS TO 20 KNOTS
ARE ANTICIPATED AT TIMES HOWEVER, WITH POTENTIALLY HIGHER GUSTS IN
AND NEAR ANY STRONGER THUNDERSTORM.

OUTLOOK...
TUESDAY THROUGH WEDNESDAY NIGHT...SUB SMALL CRAFT ADVISORY CONDITIONS
OUTLOOKED WITH THE SURFACE HIGH PRESSURE SYSTEM NEARBY.

THURSDAY AND THURSDAY NIGHT...THE CLOSEST PASS TO SMALL CRAFT
ADVISORY CONDITIONS AS THE SOUTHWEST GRADIENT INCREASES PRECEDING
THE COLD FRONTAL PASSAGE. FOR NOW WE HAVE CONDITIONS PEAKED BELOW
CRITERIA.  THERE COULD BE SOME SPECIAL MARINE WARNING RELATED
PRODUCTS NEEDED.

FRIDAY...MORE CONFIDENT ABOUT SUB SMALL CRAFT ADVISORY CONDITIONS
BEHIND THE COLD FRONT.

&&

.RIP CURRENTS...
A LONG PERIOD /10-12 SECOND/ EAST-SOUTHEAST SWELL LOOKS TO
CONTINUE, RESULTING IN A MODERATE RISK OF DANGEROUS RIP CURRENTS
THROUGH TONIGHT FOR THE NEW JERSEY AND DELAWARE COASTS.

&&

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

&&

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


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