Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 231309
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
909 AM EDT WED JUL 23 2014

.SYNOPSIS...
A COLD FRONT WILL APPROACH OUR AREA FROM THE NORTHWEST TODAY AND
CROSS THE REGION TONIGHT INTO THURSDAY MORNING. HIGH PRESSURE WILL
BUILD IN BEHIND THE DEPARTING FRONT FOR THE END OF THE WEEK INTO THE
FIRST PART OF THE WEEKEND. A COMPLEX SYSTEM WILL THEN AFFECT THE
REGION FOR SUNDAY INTO MONDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
AN UPPER-LEVEL TROUGH AMPLIFYING INTO THE NORTHEAST WILL RESULT IN
GRADUAL HEIGHT FALLS THIS AFTERNOON. THIS IS MOST NOTED HOWEVER TO
OUR NORTH AND NORTHWEST. THIS FEATURE WILL ALSO DRIVE A COLD FRONT
TOWARD OUR AREA FROM THE NORTHWEST. THE MODEL GUIDANCE SHOWS LOWER
90S ACROSS MANY AREAS THIS AFTERNOON /18C 850 MB TEMPERATURE ON THE
12Z STERLING, VA RAOB/. HOWEVER, IT WILL BE COOLER IN THE POCONOS
AND ALONG THE IMMEDIATE SHORE. GIVEN DEW POINTS NEAR 70, THE HEAT
INDEX DURING PEAK HEATING SHOULD TOP OUT IN THE UPPER 90S IN THE
WILMINGTON TO PHILADELPHIA TO TRENTON METROS. THEREFORE, NO HEAT
ADVISORY ISSUED ATTM. SOME LINGERING LOW CLOUDS MAINLY SOUTH AND
EAST OF PHILADELPHIA WILL DISSIPATE DURING THE REST OF THE MORNING.

THE AFOREMENTIONED AMPLIFYING UPPER-LEVEL TROUGH AND ARRIVING COLD
FRONT WILL TRIGGER SHOWERS AND THUNDERSTORMS. WHILE A FEW ISOLATED
CELLS CANNOT BE RULED OUT INLAND THIS AFTERNOON WITH THE HOT
AIRMASS, MOST OF OUR CONVECTION LOOKS TO WAIT FOR THE COLD FRONT TO
ARRIVE LATER THIS AFTERNOON AND THIS EVENING. THE 12Z STERLING, VA
RAOB SHOWED A CAP BETWEEN 700 MB AND 600 MB. THE SEVERE WEATHER
THREAT LOOKS RATHER LOW /NOT ZERO/ THROUGH THE DAY GIVEN A LACK OF
BULK SHEAR /500 MB WINDS LESS THAN 30 KNOTS/ AND MLCAPE CLOSER TO
1600 J/KG. AN ISOLATED DOWNBURST DAMAGING WIND GUST /DRY AIR ALOFT/
CANNOT BE RULED OUT HOWEVER ACROSS THE FAR WESTERN ZONES LATE THIS
AFTERNOON IF CONVECTION FIRES GIVEN THE HOT AIRMASS IN PLACE.

THE HOURLY GRIDS WERE TWEAKED BASED ON THE LATEST OBSERVATIONS, AND
THE LAMP/LAV GUIDANCE WAS BLENDED IN TO HELP ASSIST WITH TRENDS.
OVERALL, NO MAJOR CHANGES MADE ATTM.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
SLOW SEWD PROGRESS OF THE COLD FRONT INTO THE UNSTABLE AIRMASS SHOULD
YIELD BANDS OF TSTMS INTO THE NIGHT BUT NOT NECESSARILY WIDESPREAD.
ONE OR 2 TSTMS COULD BE SVR BUT BULK SHEAR FOR SVR IS MARGINAL AT
WORST AND ONLY THE TT AND SOME CAPE ALLOW FOR MODEST ISOLATED SVR
POTENTIAL.

PWAT 1.8 INCHES OFFERS A CHANCE OF NARROW PATHS OF 2 INCH RAINS
BENEATH THE BIGGEST STORMS.

LIGHTNING STRIKES MIGHT BE THE BIG PROBLEM?

FCST BASIS; 50 50 BLEND OF THE 00Z/23 GFS/NAM GUIDANCE IN THIS 330
AM ISSUANCE EXCEPT MOSTLY NAM METMOS TEMPS.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
THE CDFNT WILL BE EXITING THE AREA ERLY THU, BUT LINGERING SHWRS
AND TSTMS ARE STILL EXPECTED WITH ANY INSTABILITY STILL AROUND.
THE BEST CHCS ARE ERLY. THEN, HIGH PRESSURE WILL BUILD IN FROM THE
W AND DOMINATE THE WX PATN THRU THE ERLY PART OF THE WEEKEND.

DRY WX IS THEN EXPECTED THRU SAT. AS THE HIGH SLOWLY MOVES EWD,
THE FLOW WILL BECOME MORE SLY AND SWLY AND EXPECT A RISE IN TEMPS
AND HUMIDITY BY THE WEEKEND.

THEN, BY SUN, AN AREA OF LOW PRESSURE NR THE GRTLKS WILL BE MOVG
EWD. WHILE ITS EXACT TRACK IS STILL A MATTER OF DEBATE BTWN THE
MDLS, THEY DO AGREE THAT THERE WILL BE SOME KIND OF DOUBLE
BARRELED-LOW STRUCTURE BY SUN NIGHT. THERE COULD BE A WK CFP WITH
THE FIRST LOW SUN NIGHT OR MON, THE MAIN CFP WILL BE MON NIGHT OR
TUE WITH THE SECOND LOW. AGAIN, THE DETAILS WILL STILL NEED TO BE
RESOLVED AT THIS TIME SCALE, BUT THE SUN INTO MON TIME FRAME COULD
BE STORMY DEPENDING ON HOW THINGS ULTIMATELY PLAY OUT.

HIGH PRES WILL BUILD IN BEHIND THIS DEPARTING CDFNT FOR TUE. TEMPS
LOOK TO BE AT OR SLIGHTLY ABOVE NRML THRU THE PD, UNTIL THE CFP ON
TUE WHEN TEMPS WILL BE BELOW NRML. EXPECT COMFORTABLE HUMIDITY
ERLY IN THE PD, THEN INCREASING HUMIDITY IN ADVANCE OF THE CFP
ERLY NEXT WEEK.

&&

.AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

TODAY...SOME MVFR BASES FROM ABOUT KPHL ON EASTWARD /IFR AROUND KMIV
AND KACY/ SHOULD RISE TO VFR BY LATE MORNING WITH ADDITIONAL SURFACE
HEATING. OTHERWISE, VFR WITH CLOUD BASES AROUND 5000 FEET. SOME
THUNDERSTORMS ARE EXPECTED TO DEVELOP WEST OF KABE AND KRDG THIS
AFTERNOON, HOWEVER THEY MAY NOT ARRIVE TO THESE TERMINALS UNTIL
ABOUT 22Z ONWARD WITH BRIEF GUSTY WEST WINDS OF 30-40 KNOTS.
SOUTHWESTERLY WINDS INCREASING TO MAINLY 10-15 KNOTS.

TONIGHT...VFR CEILINGS WITH A BETTER CHANCE OF IFR IN THUNDERSTORMS.
LIGHT SOUTHWEST WINDS SHIFT TO THE NORTH TOWARD MORNING WHEN PATCHY
IFR STRATUS/FOG MIGHT FORM WHERE IT RAINED IN EVENING. GUSTY WEST
WINDS IN A THUNDERSTORM POSSIBLE BETWEEN 00Z AND 04Z FOR KTTN, KPNE,
KPHL, AND KILG.

OUTLOOK...
THU...MVFR AND IFR CONDITIONS AT TIMES IN SHOWERS AND
THUNDERSTORMS, ESPECIALLY EARLY. PATCHY FOG THU MORNING. MODERATE
CONFIDENCE.

THU NIGHT THROUGH SAT...MAINLY VFR UNDER HIGH PRESSURE. HIGH
CONFIDENCE.

SUN...SUB-VFR POSSIBLE IN SCATTERED SHOWERS AND THUNDERSTORMS.
MODERATE CONFIDENCE.

&&

.MARINE...
NO HEADLINES THROUGH TONIGHT.

MAINLY S-SW WIND G UNDER 20 KT SHIFT TO NORTH TOWARD DAWN THURSDAY.

WAVE HEIGHTS ON OUR OCEAN WATERS SHOULD BE 2 TO 4 FEET. WAVES ON
DELAWARE BAY ARE EXPECTED TO BE 2 FEET OR LESS.

SCATTERED THUNDERSTORMS TONIGHT.

OUTLOOK...
THU THROUGH SAT...NO MARINE HEADLINE EXPECTED WITH HIGH PRES
OVERHEAD.

SUN...INCREASING SEAS AHEAD OF NEXT SYS MAY YIELD SCA, ESPECIALLY
N BY LATER IN THE DAY.

&&

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

&&

$$
SYNOPSIS...NIERENBERG
NEAR TERM...GORSE
SHORT TERM...DRAG
LONG TERM...NIERENBERG
AVIATION...DRAG/GORSE/NIERENBERG
MARINE...DRAG/NIERENBERG




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