National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 161813
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
213 PM EDT SUN JUN 16 2013

.SYNOPSIS...
A HIGH PRESSURE SYSTEM CRESTING THE APPALACHIANS WILL MOVE
OFFSHORE TODAY. AN AREA OF LOW PRESSURE WILL TRACK FROM THE GREAT
LAKES INTO SOUTHEASTERN CANADA LATER TODAY INTO MONDAY. ITS FIRST
COLD FRONT IS EXPECTED TO DISSIPATE AS IT MOVES THROUGH THE AREA
LATE TONIGHT. ITS NEXT COLD FRONT IS SCHEDULED TO MOVE THROUGH ON
TUESDAY WITH POSSIBLY A NEW WAVE OF LOW PRESSURE FORMING ALONG IT.
A HIGH PRESSURE SYSTEM WILL THEN BUILD INTO THE FORECAST AREA
WEDNESDAY AND THURSDAY, BEFORE SHIFTING TO OUR EAST FRIDAY INTO
SATURDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
12Z KIAD RAOBS SHOW A DECENT CAP RIGHT AROUND 800MB, JUST BELOW THE
STRONGEST WARM AIR ADVECTION LAYER WITH CONVECTIVE TEMPERATURES
WELL OUT OF REACH TODAY. KPBZ SHOWS LITTLE TO NO CAP WITH LOWER
CONVECTIVE TEMPERATURES AND STRONGER LOW-LEVEL SHEAR AS THE 850MB
JET GETS GOING. THE BIG ISSUES FOR TODAY WOULD BE THE EXTENT OF
THE CLOUD COVER AND A BOUNDARY LAYER THAT IS NOT VERY MOIST. IT
APPEARS DOUBTFUL THAT WE WILL SEE A LOT OF BREAKS IN THE CLOUDS
THIS AFTERNOON TO HELP WITH SURFACE HEATING GIVEN THE STRONG MID-
LEVEL FLOW THAT KEEPS PUMPING IN MORE MOISTURE FROM THE WEST.
GRANTED WE WILL EVENTUALLY SEE THE LOW-LEVEL JET MAKES ITS WAY
TOWARDS OUR REGION LATER TODAY BUT IT LOOKS TO BE TOO LITTLE TO
LATE FOR CONVECTIVE PURPOSES. ALL- IN- ALL THIS WOULD SUGGEST
THAT WE EITHER NEED A VERY STRONG SURFACE FOCUS, WHICH WE DON`T OR
WILL NOT HAVE TO OVERCOME THE LACK OF SURFACE HEATING, OR STORMS
HAVE TO ADVECT IN FROM THE WEST- SOUTHWEST AND BE ABLE TO MAINTAIN
THEMSELVES WITHIN THEIR OWN ENVIRONMENT. STILL EXPECT SHOWERS TO MOVE IN
AHEAD OF A SURFACE TROUGH FROM OUR WEST SO WE KEPT IN THE HIGH
CHANCE-LIKELY POPS FOR THIS EVENING.

TEMPERATURES WILL RISE AS WARMER AIR IS ADVECTED INTO THE REGION
IN THE SOUTHWEST FLOW, EVEN THOUGH WE WILL HAVE PLENTY OF CLOUD
COVER AROUND. EXPECT MAXIMUM TEMPERATURES TO BE IN THE 80S ACROSS
MOST OF THE AREA TODAY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
THE AFOREMENTIONED SURFACE TROUGH MOVES THROUGH THE AREA TONIGHT
WITH SHOWERS AND THUNDERSTORMS ACCOMPANYING IT. AS THE TROUGH MOVES
TO THE EAST, WE WILL LOSE THE CONVECTIVE FOCUS AND SHOWERS AND
THUNDERSTORMS SHOULD START TO DIMINISH.

IN THE WAKE OF THE TROUGH, WE SHOULD BE ABLE TO LOSE SOME OF OUR
CLOUDINESS AND BECOME PARTLY CLOUDY AS WE HEAD TOWARD MORNING.

TEMPERATURES WILL REMAIN ON THE WARM SIDE AS WE HAVE EXTENSIVE
CLOUDINESS ACROSS THE REGION. EXPECT LOWS TO BE IN THE 60S ACROSS
THE AREA.

&&

.LONG TERM /MONDAY THROUGH SUNDAY/...
WHILE THE GFS INITIALIZATION LOOKED BETTER FROM A HEIGHT FIELD
PERSPECTIVE AT 500MB, THE OBSERVED WINDS LOOKED BETTER OFF THE
WRF-NMMB. THE PROBLEM LIES IN THE EVENTUAL EVOLUTION OF THE TROF
THROUGH THE MIDDLE OF THE WEEK WITH THE GFS IN ITS USUAL FAST
TIMING POSN. THERE HAS NOT BEEN CLOSE RUN TO RUN CONTINUITY WITH
THE MODEL ON THIS AND THUS THIS FCST PACKAGE IS GOING TO SHY AWAY
FROM IT, COMING CLOSER TO A SREF AND UKMET SOLN IN THE NEARER LONG
TERM AND A CONTINUITY/LATEST HPC THOUGHTS IN THE FURTHER LONG
TERM. IN GENERAL THE WRF-NMMB LOOKED BETTER AT 925MB AND 850MB,
ALTHOUGH THE THERMAL DIFFERENCES INTO TUESDAY ARE MORE OF TIMING.

AN INITIAL COLD FRONT IS EXPECTED TO DISSIPATE AS IT MOVES THROUGH
OUR CWA EARLY MONDAY. IN ITS WAKE WESTERLY FLOW IS PREDICTED TO OCCUR
AS IS MID LEVEL CAPPING TO DEVELOP. WE HAVE EXPANDED ON THE IDEA
OF THE POTENTIAL FOR A DRY MONDAY LIMITING POPS TO THE SE CWA IN
THE MORNING WHERE CAPPING MAY NOT BE IN PLACE IN TIME AND THE FAR
NORTHWEST WHERE ITS EROSION FROM A PREDICTED APPROACHING SHORT
WAVE MIGHT ARRIVE BY THE END OF THE DAY. OUR CWA IS ALSO PREDICTED
TO BE ON THE CONVERGENT SIDE OF THE APPROACHING 250MB JET WITH NO
FCST MID LEVEL QVEC CONVERGENCE. ALL POINT TO RELATIVELY LOW POPS
IF ANY. NOT MANY CHANGES TO MAX TEMPS. REMAINED RELATIVELY
CONSERVATIVE WITH THEM GIVEN THE RECENT WETNESS. ACTUAL MAX TEMPS
EVEN WEST OF US VS TRADITIONAL 1000-850MB THICKNESS VALUES HAVE
NOT BEEN THAT ROBUST.

A SECOND COLD FRONT IS PREDICTED TO APPROACH OUR CWA ON MONDAY NIGHT
OR IF ONE WOULD FOLLOW THE GFS CLEAR MOST OF THE AREA BY MORNING.
REGARDLESS OF THE GFS TIMING, ANY ONGOING CONVECTION THAT DEVELOPS
IN MORE FAVORABLE REGIONS WOULD STAND THE CHANCE OF SURVIVING. PLUS
WE ARE FORECAST TO GET INTO A MORE FAVORABLE QUADRANT OF THE JET
ALOFT. MIN TEMPS NOT FAR FROM STAT GUIDANCE.

THEN TUESDAY IN PARTICULAR, (NOT AS CONFIDENT ABOUT TUESDAY
NIGHT) WE MAINTAINED POPS AND CHOSE A CLOSER TO SREF SOLUTION FOR
THE POSITIONING OF THE COLD FRONT AND THE WAVE ON IT. ONLY BOWING
TO THE GFS IS TO PLACE HIGHER POPS SE BOTH PERIODS. EVEN THE
PRESENT GFS SOLN KEEPS OUR CWA IN THE FAVORABLE ENTRANCE REGION OF
THE 250MB JET TUESDAY WITH FCST MID LEVEL QVEC CONVERGENCE PRETTY
MUCH THRUT OUR AREA. AS FAR AS STRONG/SEVERE THREAT IS CONCERNED, THE
FCST CAPES ARE NOT THAT ROBUST, ALTHOUGH THE BULK SHEAR WILL BE
INCREASING. A BIT CONCERNED ABOUT CLOUDINESS PUTTING A LID PER SE
ON TSRA STRENGTH. LATEST GUIDANCE SUGGEST IF THERE WOULD BE A SPOT
FOR STRONGER STORMS, IT WOULD BE IN THE SERN PART OF OUR CWA. NOT
PARTICULARLY CONFIDENT ABOUT MAX TEMPS BECAUSE OF THE COMPLICATION
FROM SKY COVER AND DIFFERENCES IN FRONTAL POSNS. SINCE ANDREA MOST
OF OUR PCPN CHANCES HAVE BEEN OUTPERFORMING AND WHILE SOME OF THE
MEDIUM RANGE MODEL OUTPUT HAS SOME GRIDSCALE FEEDBACK LOOK TO
THEM, THE FCST PWAT ARE EXPECTED TO GET TO AROUND 1.5". AT THE
LEAST SOME TYPICALLY OR LOCALLY HEAVY DOWNPOURS WOULD BE POSSIBLE.

NO BIG CHANGES THEN WERE MADE FOR THE REST OF THE LONG TERM. DONT
KNOW HOW MANY MORE OF THESE WE WILL HAVE THIS MET SUMMER, BUT ANOTHER
REFRESHING CANADIAN AIR MASS IS FORECAST TO ARRIVE FOR WEDNESDAY
AND THURSDAY BEFORE THE ATTENDING HIGH PRESSURE SYSTEM MOVES
OFFSHORE. THE RETURN FLOW WILL NOT ONLY BRING IN HIGHER TEMPS, BUT
ALSO A CHANCE FOR MORE THUNDERSTORMS AS A WEAK WARM FRONT MOVES
THROUGH THE AREA.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

THIS EVENING - TONIGHT...VFR. SOUTHWEST WINDS BETWEEN 10-15KTS WITH
GUSTS REACHING INTO THE LOW-20KTS. A WEAK TROUGH/COLD FRONT IS
PROGGED TO SLIDE THROUGH LATER THIS EVENING AND COULD TOUCH OFF A
FEW SHOWERS WITH POSSIBLY A THUNDERSTORM. UPDATED CCFP SHOWS HIGH
CONFIDENCE OF SPARSE COVERAGE THROUGHOUT MOST OF OUR AREA. GIVEN THE
TIMING OF THE EVENT WE MAINTAIN THE TEMPO FOR THUNDER FOR ALL
TERMINALS EXCEPT ACY/MIV. AT MIV/ACY CONFIDENCE IS LOWER THAT STORMS
WOULD BE ABLE TO MAINTAIN THUNDER THROUGH THE LATE EVENING HOURS,
THEREFORE WE CONTINUE TO HOLD OFF ON PLACING A TEMPO GROUP IN THEM.

AFTER THE SHOWERS MOVE THROUGH THE WINDS WILL BECOME LIGHT FROM THE
SOUTHWEST. WITH A NEW MOISTER AIRMASS IN PLACE AND ONLY HIGH CLOUDS
IN PLACE SOME TERMINALS COULD SEE MVFR VSBYS FORM BY LATE MORNING
WITH EITHER A LIGHT GROUND FOG OR HAZE.

MONDAY...VFR. ANY GROUND FOG/HAZE WILL DISSIPATE BY LATE MORNING
ONCE WE BEGIN TO MIX. WINDS SHOULD BACK A BIT TOWARDS THE WEST BUT
REMAIN LIGHT. THERE COULD BE SOME GUSTINESS AGAIN TOMORROW AFTERNOON
BUT SHOULD BE IN THE UPPER TEENS RANGE. ANOTHER CHANCE OF ISOLATED
SHOWERS AND THUNDERSTORMS POSSIBLE.

OUTLOOK...
MONDAY NIGHT AND TUESDAY...AVERAGING VFR, HOWEVER MVFR OR LOWER
AT TIMES IN SHOWERS AND THUNDERSTORMS.

TUESDAY NIGHT...VFR WITH SOME POCKETS OF MVFR OR IFR AT OUTLYING
AIRPORTS AND TERMINALS IN FOG AND ANY RESIDUAL PRECIPITATION EARLY.

WEDNESDAY AND THURSDAY...VFR.
-- End Changed Discussion --

&&

.MARINE...
A SMALL CRAFT ADVISORY WILL BE IN EFFECT FROM THIS AFTERNOON THROUGH
LATE TONIGHT ON THE OCEAN WATERS.

CONDITIONS ON THE AREA WATERS WILL START OFF FAIRLY BENIGN TODAY AS
HIGH PRESSURE SETTLES TO OUR SOUTHEAST. SEAS WILL GRADUALLY START TO
BUILD IN THE SOUTH TO SOUTHWEST FLOW AND WILL START TO APPROACH 5
FEET THIS AFTERNOON AND WILL THEN REMAIN NEAR 5 FEET THROUGH MUCH OF
TONIGHT. WINDS WILL GUST AROUND 20 KNOTS ON THE WATERS TODAY. WHILE
THE WINDS JUST ABOVE THE SURFACE LOOK TO BE IN THE 25 TO 30 KNOT
RANGE, AN INVERSION OVER THE WATER AS WARMER AIR MOVES IN, WILL
PREVENT THEM FROM MIXING EFFICIENTLY DOWN TO THE SURFACE. A FEW
GUSTS UP TO 25 KNOTS MAY OCCUR, ESPECIALLY LATER THIS AFTERNOON.

OUTLOOK...
UNCERTAINTY HIGHER THAN AVERAGE BECAUSE OF MODELING DIFFERENCES WITH
RESPECT TO THE DEVELOPMENT OF A WAVE OF LOW PRESSURE ON THE FRONT
ABOUT TUESDAY. FOR MONDAY SMALL CRAFT ADVISORY CONDITIONS (MAINLY
SEAS ON THE OCEAN) MIGHT LINGER INTO THE MORNING BEFORE THE
WEAKENING FIRST FRONT LOOSENS THE PRESSURE GRADIENT. AFTER THAT, THE
NEXT WAVE OF LOW PRESSURE MIGHT BE STRONG ENOUGH TO BRING SMALL
CRAFT ADVISORY CONDITIONS (5 FOOT SEAS) BACK TO THE OCEAN ZONES ON
TUESDAY. THEN THE CIRCULATION BETWEEN THAT WAVE OF LOW PRESSURE AND
APPROACHING HIGH PRESSURE SYSTEM MIGHT CAUSE WIND GUSTS TO BE CLOSE
OR REACH SMALL CRAFT ADVISORY CRITERIA LATER TUESDAY INTO WEDNESDAY
ACROSS OUR ENTIRE MARINE AREA. AS THE HIGH PRESSURE SYSTEM IS
FORECAST TO COME CLOSER LATER WEDNESDAY INTO THURSDAY, WE ARE MORE
CONFIDENT ABOUT SUB SMALL CRAFT ADVISORY CONDITIONS OCCURRING ON
ALL OF THE AREA WATERS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT MONDAY FOR ANZ450>455.
-- End Changed Discussion --

&&

$$
SYNOPSIS...GIGI/GORSE
NEAR TERM...HEAVENER/MEOLA
SHORT TERM...MEOLA
LONG TERM...GIGI
AVIATION...GIGI/GORSE/HEAVENER
MARINE...GIGI/MEOLA