Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000
FXUS61 KPHI 262359
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
759 PM EDT SUN JUL 26 2015

.SYNOPSIS...
A COLD FRONT WILL APPROACH THE REGION TONIGHT FROM THE NORTHWEST. BY
MONDAY, THIS FRONT WILL DISSIPATE INTO A TROUGH OF LOW PRESSURE.
HIGH PRESSURE WILL THEN BUILD EASTWARD INTO THE REGION FOR THE
MIDDLE OF THE WEEK BEFORE ANOTHER COLD FRONT COMES THROUGH THE
REGION THURSDAY NIGHT. ANOTHER AREA OF HIGH PRESSURE WILL BUILD
EASTWARD FOR THE END OF NEXT WEEK WITH A FRONTAL BOUNDARY LOCATED TO
OUR SOUTH.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
THE WEAKENING COLD FRONT/WIND SHIFT ACROSS THE CENTRAL PART OF
PENNSYLVANIA WILL SLOWLY DRIFT TOWARDS THE EAST-SOUTHEAST TONIGHT.
SCATTERED SHOWERS AND THUNDERSTORMS WILL TRY TO PENETRATE OUR
NORTHERN ZONES LATER THIS EVENING AHEAD OF THE FRONT, OR WHAT EVER
IS LEFT OF IT. THERE IS NEARLY 1000J/KG OF DCAPE AS THE AIRMASS
CONTINUES TO MODIFY ON THE MOISTER SIDE. MID-LEVEL LAPSE RATES ARE
RATHER VANILLA THOUGH WITH THE STRONGER HEATING OF THE DAY THE LOW-
LEVEL LAPSE RATES HAVE INCREASED CLOSER TO DRY ADIABATIC IN THE 0-
3KM LAYER. THE STORMS ARE MORE PULSEY WITH SHEAR BEING ON THE WEAKER
SIDE...15 KNOTS MAYBE, THOUGH PRECIP LOADING IN THE COLUMN COULD
PRODUCE AN ISOLATED STRONGER WIND GUST ALONG WITH HEAVY RAIN. THE
MEAN FLOW ALOFT TOO IS WEAK SO THE STORMS MAY SIT AND CYCLE FOR A
WHILE OVER THE SAME AREA CAUSING LOCALIZED POOR DRAINAGE FLOODING
ISSUES.

AS THE EVENING AND NIGHT WEAR ON THE AMOUNT OF SURFACE BASED
INSTABILITY LESSENS AND WHATS LEFT OF THE LOW-LEVEL JET MOVES
FARTHER TOWARDS THE NORTHEAST. THERE IS NOT A LOT OF SURFACE
SYNOPTIC LIFTING LEFT TONIGHT BUT WEAK MID-LEVEL COLD POOL
INTERACTION WITH A FEW PASSING SHORTWAVES MAY KEEP THE SHOWERY
ACTIVITY GOING THROUGH THE OVERNIGHT HOURS...THE CHANCES INCREASE
FROM NORTHWEST TO SOUTHEAST LATE TONIGHT.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
ALMOST A WASH-RINSE-REPEAT KIND OF DAY ON MONDAY. WIND SHIFT LINE
STILL HANGING AROUND THE REGION THOUGH EVEN MORE DIFFUSE THAN ON
SUNDAY. AMPLE LOW-LEVEL MOISTURE WITH TOTAL COLUMN PWATS CONTINUING
TO CLIMB ABOVE 1.5 INCHES. A FEW PASSING SHORTWAVES ALOFT RIDING
ALONG ANY SURFACE CONVERGENCE BOUNDARY WILL HELP TO INITIATE
AFTERNOON CONVECTION, BUT AGAIN THE HIGHER TERRAIN/RIDGE TOPS MAY BE
THE FOCUS AGAIN. OVERALL WE MAINTAIN THE CHANCE POPS FOR SCATTERED
SHOWERS AND THUNDERSTORMS. TEMPERATURES WERE BUMPED UP SEVERAL
DEGREES FROM MOS WITH THE THINKING THAT MOS IS TRYING TO WASH US OUT
TOO MUCH TOMORROW AFTERNOON. SURFACE FLOW DOESN`T CHANGE ALL THAT
MUCH FROM DAY TO DAY AND THE LOW-LEVEL THERMAL PROFILE DOES COOL
EVER SO SLIGHTLY, BUT WE FEEL WE`LL HAVE ANOTHER CHANCE AT REACHING
90F MONDAY AFTERNOON...TOO MUCH MIXING FROM ALOFT ADIABATICALLY.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
MONDAY NIGHT THROUGH WEDNESDAY NIGHT: A GRADUAL CONTINUED UPTICK IN
HEAT AND HUMIDITY WITH A STRONG RIDGE ACROSS THE SOUTHERN PLAINS
MAKING ANOTHER CHARGE INTO THE REGION WITH RISING HEIGHTS. THIS
WILL RESULT IN A MAINLY DRY PERIOD (POSSIBLE EXCEPTION OF AN
ISOLATED THUNDERSTORM SOUTH TUESDAY AFTERNOON). FOR ACTUAL HIGH
TEMPERATURES, MODELED 925 MB TEMPERATURES RISE FROM AROUND 23C ON
TUESDAY TO 25C FOR WEDNESDAY. THIS EQUATES TO HIGH TEMPERATURES
STARTING OFF AROUND 90 ON TUESDAY THEN RISING INTO THE MID 90`S
FOR WEDNESDAY, STARTING ANOTHER POTENTIAL MODELED HEAT WAVE FOR
MOST OF THE REGION. LESS SPREAD IN PRESENT IN THE OPERATIONAL
MODELS AND THE ENSEMBLES IN THIS PERIOD COMPARED TO YESTERDAY AS
THE GFS HAS TRENDED COOLER WITH TEMPERATURES. FORTUNATELY MODELED
DEWPOINTS ARE IN THE LOW/MID 60`S DURING THE PEAK HEATING HOURS
BOTH TUESDAY AND WEDNESDAY. THIS WOULD LIMIT THE MAXIMUM HEAT
INDEX TO BETWEEN 95 AND 100 DEGREES.


THURSDAY THROUGH SUNDAY: THE COLD FRONTAL BOUNDARY APPROACHING THE
REGION TO START THIS PERIOD WILL LIKELY BE THE TRIGGER FOR AN
INCREASE IN CLOUDS AND SOME SCATTERED AFTERNOON/EVENING SHOWERS AND
STORMS ON THURSDAY. ONCE AGAIN, THE LACK OF SHEAR LOOKS TO BE A
LIMITATION IN THE WAY OF ANY SEVERE WEATHER. HOWEVER, AN ISOLATED
STRONG WIND GUST CAN NOT BE RULED OUT.

THE 12Z (DAYTIME) RUNS OF THE GFS CONTINUE TO RUN WARMER AND DRIER
ON THURSDAY THAN OTHER MODELS AND GFS RUNS, CURRENT THINKING IS THIS
AN ANOMALY RATHER THAN THE RULE AND THE FORECAST WILL GO MORE
TOWARD THE ECMWF WITH TEMPERATURES ON THURSDAY. HIGHER HUMIDITY
THOUGH GIVES THE REGION A HIGHER CHANCE FOR THE HEAT INDEX TO
REACH 100 DEGREES IN PARTS OF THE REGION.

SOME DRIER AND PERHAPS SLIGHTLY COOLER AIR IS LIKELY TO END THE
POTENTIAL HEAT WAVE BEHIND THE FRONT ON FRIDAY. COMPARED TO JUST
YESTERDAY, THE OPERATIONAL MODELS AND THE RESPECTIVE ENSEMBLES
ARE FARTHER OFFSHORE WITH THE FRONT AND ARE SHOWING A MUCH LOWER
THREAT FOR WAVES OF LOW PRESSURE DEVELOP ALONG THE BOUNDARY. THE
FORECAST REFLECTS A DRY BUT STILL HOT CONDITIONS NEXT WEEKEND WITH
EVEN WARM AIR ADVECTION AGAIN BY NEXT SUNDAY WITH A FRONTAL
PASSAGE TO OUR NORTH.

&&

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

TONIGHT...MOSTLY VFR CONDITIONS EXPECTED. ISOLATED THUNDERSTORMS
AND SCATTERED SHOWERS ARE POSSIBLE THROUGH THE OVERNIGHT HOURS.
HOWEVER, WITH LIMITED COVERAGE, DON`T HAVE ENOUGH CONFIDENCE TO
INCLUDE MENTION IN ANY TAFS EXCEPT KRDG AND KABE. IF ANY OF THE
OTHER TAF SITES ARE AFFECTED, IT WILL LIKELY BE 06Z OR LATER.
PATCHY BR IS POSSIBLE ESPECIALLY FOR ANY TAF SITES THAT DO
RECEIVE RAIN OVERNIGHT, OR IF FLOW STAYS MORE OF AN ON SHORE
DIRECTION FOR OUR COASTAL/NEAR COASTAL SITES (KILG, KMIV, AND
KACY).

MONDAY...MOSTLY VFR. MORE SCATTERED SHOWERS AND THUNDERSTORMS ARE
POSSIBLE IN THE AFTERNOON HOURS BUT TOO HARD TO PINPOINT AT THIS
TIME. WINDS REMAIN MOSTLY OUT OF THE SOUTH, SLIGHTLY SOUTHEAST.


OUTLOOK...
MONDAY NIGHT: VFR, ISOLATED TO SCATTERED SHOWERS THUNDERSTORMS, MAY
BRIEFLY REDUCE VISIBILITIES AND CEILINGS. WINDS AT OR UNDER UNDER
10 KNOTS OUTSIDE OF THUNDERSTORMS.

TUESDAY THROUGH WEDNESDAY NIGHT: VFR. WINDS AT OR UNDER 10 KNOTS
THROUGH MOST OF THE PERIOD, WITH SOME SOUTHWESTERLY WIND GUSTS
AROUND 15 KNOTS WEDNESDAY AFTERNOON.


THURSDAY AND THURSDAY NIGHT: VFR, ISOLATED TO SCATTERED SHOWERS
THUNDERSTORMS, MAY BRIEFLY REDUCE VISIBILITIES AND CEILINGS.
WEST- SOUTHWEST WIND GUSTS AROUND 15 KNOTS POSSIBLE THURSDAY AND
EVENING, LOCALLY HIGHER GUSTS IN THUNDERSTORMS.

FRIDAY AND FRIDAY NIGHT: VFR. WINDS AT OR UNDER 10 KNOTS.

&&

.MARINE...
SUB-SCA CONDITIONS EXPECTED TONIGHT AND TOMORROW AS A WEAK SURFACE
FRONT TRIES TO PUSH THROUGH. SOUTHERLY WINDS AROUND 10 TO 15 KNOTS
WITH SOME GUSTS UPWARDS OF 20 KNOTS STILL POSSIBLE TONIGHT AND
TOMORROW. SEAS DO INCH UP UNDER THE SOUTHERLY FLOW TONIGHT AND
TOMORROW BUT SHOULD REMAIN 4 FEET OR LESS.

OUTLOOK...

SEAS AND WINDS LOOK TO REMAIN BELOW SCA CRITERIA THROUGH
FRIDAY. ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARE
POSSIBLE MONDAY NIGHT AND THURSDAY AFTERNOON/EVENING WITH THE
POTENTIAL FOR LIGHTNING A STRONG WIND GUST OR TWO. SEAS OVERALL
FOUR FEET OR LESS WITH WIND GUSTS 20 KNOTS OR LESS THROUGH
THURSDAY. SEAS BUILDING TO AROUND FIVE FEET WITH SOME ISOLATED 25
KNOT FOR A PERIOD THURSDAY NIGHT BEFORE DECREASING ON FRIDAY.

&&

.RIP CURRENTS...
WITH THE LONG PERIOD (11-12 SECOND) 1 TO 2 FOOT EASTERLY SWELL
CONTINUING...EXPECT THE MODERATE RISK OF DANGEROUS RIP CURRENTS TO
ALSO CONTINUE TODAY.

&&

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

&&

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



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