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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 150128
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
928 PM EDT TUE MAY 14 2013

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE SOUTHEAST COAST TONIGHT AND OUT TO
SEA INTO THURSDAY. A WARM FRONT IS FORECAST TO LIFT THROUGH OUR AREA
ON EARLY WEDNESDAY, FOLLOWED BY A COLD FRONT WEDNESDAY NIGHT. THIS
FRONT WILL SAG TO OUR SOUTH AND STALL FOR THE LATE WEEK PERIOD AND
INTO THE WEEKEND. THE FRONT MAY LIFT BACK NORTHWARD ACROSS THE AREA
AS A WARM FRONT EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
-- Changed Discussion --
PCPN PRECEDING THE WARM FRONT LOOKS MORE MENANCING ON THE 88D(S)
THAN REALITY AS OUR AIR MASS REMAINS RELATIVELY. WHERE PCPN IS
REACHING THE GROUND AS SPRINKLES IS OCCURRING WHEN TEMP AND DEW
POINT SPREADS ARE LESS THAN 20F AND A .01/HR MEASURABLE WHEN THE
SPREAD CLOSES IN TO LESS THAN 10F. OUR CWA STILL HAS A LITTLE WAY
TO GO BASED ON CURRENT OBS TO GET TO MEASURABLE. WE HAVE THE GRIDS
STARTING AS SPRINKLES LIKELY AND THEN LEFT THE CONVERSION TO
SCATTERED SHOWERS OVERNIGHT. THE EMPHASIS REMAINS IN THE
SOUTHWESTERN HALF OF OUR CWA WITH THE HIGHEST CHANCES.

WE ARE SEEING SOME DISPARITY IN TEMOPERATURES AS SOME SHELTERED
LOCALES ARE DECOUPLING AND CLOUDS ARE YET TO MOVE IN NORTHEAST.
THIS BUMPINESS WITH TEMPERATURES WE ARE EXPECTING TO SMOOTH
OVERNIGHT AS WINDS INCREASE NEAR THE SURFACE AND CLOUDS ROLL IN.
DEW POINTS ARE RESPONDING SLOWLY, SO WE SLOWED THEIR ASCENT
SLIGHTLY. BOTTOM LINE OVERALL CHANGES NOT THAT DRASTIC.

50 50 BLENDED 12Z/14 NCEP MOS GUIDANCE FOR TEMPS/WINDS/DEWS.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
-- Changed Discussion --
CONCERN ABOUT ADEQUATE MOISTURE OR LESS MOISTURE THAN WHAT THE
MODELS ARE THINKING AS MENTIONED BELOW IS COMING TO FRUITION THIS
EVENING. BOTH THE GFS AND WRF-NMMB WERE 10F TO AS MUCH AS 20F TOO
HIGH WITH THEIR SFC DEW POINT TEMP FCSTS VALID AT 00Z IN THE UPPER
MISSISSIPPI VALLEY AND EVEN ABOUT 5-10F TOO HIGH IN THE LOWER OHIO
AND TENNESSEE VALLEYS. MOS STAT GUIDANCE LOOKS MUCH BETTER THAN
RAW MODEL DATA AT THIS POINT.

WEDNESDAY...THE 12Z GFS LOOKS LIKE MY IDEA OF A BEST MODEL SOLN OF
THE 12Z INTERNATIONAL SUITE. THE 12/14 GFS IMO HAS THE RIGHT IDEA
ABOUT STRONG CONVECTION AND PROBABLY STREAMING EAST SOUTHEAST FROM
SOUTHERN PA ACROSS S NJ AND OR THE DELMARVA LATE IN THE DAY WEDNESDAY.
SPC 1715Z SWODY2 ASSESSMENT MATCHES MY THINKING.

THE INCREASING BOUNDARY LAYER MOISTURE MAY BE OVERDONE BY THE MODELS,
THUS LIMITING INSTABILITY AND THE POTENTIAL FOR INITIATING CONVECTION.

THE 18Z GFS LAMP HAS GRIDDED LAMP TSTM PROBS IN W NYS AND NW PA BY
14Z.

MODEL REMNANTS OF AN EML NOW SPREADING EWD FROM THE MIDWEST THAT
SUPPORTS CONCERN FOR HAILERS....INCREASING THE 700-500MB LAPSE
RATES LATE IN THE DAY.

MORE THAN ADEQUATE BULK SHEAR FOR SVR WIND... AND SO THE QUESTION
BECOMES...IS THERE ENOUGH MOISTURE TO SUPPORT TSTM GENERATION. 12Z/14
GFS ML CAPE IS ONLY 600J LATER IN THE DAY AND SO DID NOT WORD HAIL
OR GUSTY WINDS IN THE ZONE PRODUCTS.

OTRW TEMPS/WINDS/DEWS ARE 50 50 BLENDED 12Z/14 NCEP MOS GUIDANCE
WITH A LEAN TO A WARMER TEMP SOLN SINCE MOST OF THE DAY SHOULD
BE RAINFREE.

CONFIDENCE ON POPS IS BELOW AVG AND I MAY BE OVER FCST THE CHC OF
A SHOWER OR TSTM WED AFTN.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
THE PRE-FRONTAL SURFACE TROUGH AND ANY ASSOCIATED CONVECTION SHOULD
BE PROGRESSING THROUGH THE AREA DURING THE EARLY EVENING TIME
WEDNESDAY. ONCE THE TROUGH MOVES THROUGH AND THE SUN GOES DOWN,
ANY CONVECTION SHOULD DIMINISH. THE ACTUAL COLD FRONT IS NOT
EXPECTED TO MOVE THROUGH THE AREA UNTIL WEDNESDAY NIGHT. THERE
STILL COULD BE A FEW SHOWERS AROUND UNTIL THE FRONT ACTUALLY MOVES
THROUGH, BUT ANY THUNDERSTORM ACTIVITY SHOULD HAVE ENDED BY THE
TIME THE FRONT APPROACHES.

THE AFOREMENTIONED COLD FRONT WILL SAG TO OUR SOUTH THURSDAY INTO
FRIDAY, WHILE THE PARENT LOW WILL SPIN THROUGH NEW ENGLAND AND
INTO THE CANADIAN MARITIMES. THIS WILL KEEP A STEADY WEST TO
NORTHWEST FLOW ACROSS THE AREA. EVEN THOUGH A WEAK SURFACE TROUGH
IS FORECAST TO CROSS THE AREA ON THURSDAY, MOST OF THE AREA SHOULD
REMAIN DRY THURSDAY AND FRIDAY. THE EXCEPTION TO THIS WILL BE
ACROSS THE SOUTHERN THIRD OF THE AREA, WHICH WOULD BE CLOSE TO THE
OLD COLD FRONT AS IT SLOWLY SAGS TO OUR SOUTH, BEFORE STALLING.
THERE MAY BE ENOUGH MOISTURE AND LIFT TO CREATE A FEW SCATTERED
SHOWERS/THUNDERSTORMS ACROSS SOUTHERN NEW JERSEY AND THE DELMARVA.

AS WE MOVE INTO THE WEEKEND, THE LOW TO OUR NORTHEAST WILL SLIDE OUT
TO SEA, ALLOWING FOR HIGH PRESSURE TO BUILD ACROSS THE NORTHEAST.
THIS HIGH IS EXPECTED TO PUSH OFF THE NEW ENGLAND COAST AND TO
OUR EAST THROUGH THE WEEKEND. THIS WILL PUT OUR AREA INTO AN
EASTERLY/SOUTHEASTERLY FLOW FOR MUCH OF THE WEEKEND, WHICH COULD
HELP KEEP OUR TEMPERATURES FRONT RISING VERY MUCH. IT MAY ALSO
KEEP SOME CLOUD COVER ACROSS THE AREA, AND WITH AN INCREASE IN
MOISTURE, ANY ADDITIONAL LIFT COULD LEAD TO SOME PRECIPITATION.
FOR NOW WE ONLY KEEP CHANCE/SLIGHT CHANCE POPS THROUGH THE
WEEKEND.

THE FRONT THAT STALLS TO OUR SOUTH IS EXPECTED TO BEGIN LIFTING
BACK NORTHWARD AS A WARM FRONT BY LATE SUNDAY INTO MONDAY. THIS
COULD LEAD TO SOME SHOWER ACTIVITY SUNDAY NIGHT INTO MONDAY. THEN
WE WAIT AND SEE WHAT HAPPENS WITH THE NEXT SYSTEM AS IT MOVES OUT
OF THE CENTRAL/NORTHERN PLAINS AND THROUGH THE GREAT LAKES.
GFS/ECMWF DIFFER ON HOW FAST THEY MOVE THE SYSTEM. IT`S POSSIBLE
IT COULD GET HERE AS EARLY AS WEDNESDAY, BUT WE WILL SEE HOW
MODELS HANDLE IT OVER THE NEXT FEW DAYS.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

THE 00Z TAFS, THE TERMINALS WERE KEPT VFR ALTHOUGH CONFIDENCE IS
NOT HIGH LATE WEDNESDAY AFTERNOON.

FOR TONIGHT, WE BRING IN A MID DECK VFR CIG AND SLOWLY BACK THE
WINDS FROM WESTSOUTHWEST TO SOUTHEAST OVERNIGHT WITH SPEEDS
GENERALLY LESS THAN 10 KNOTS. THE FORECAST WIND GROUPS REPRESENT
AN AVERAGE DIRECTION FOR THE HOURS THE FCST PERIOD IS VALID. WE
DO CARRY THE MENTION OF NON RESTRICTING SHOWERS (EXCEPT AT KABE
AND KRDG) FOR A COUPLE OF HOURS LATER TONIGHT. SO FAR WE HAVE NOT
SEEN ANY VSBY RESTRICTIONS UPSTREAM.

THEN ON WEDNESDAY WE ARE FORECASTING ANOTHER MID DECK VFR CIG TO
PREVAIL. THE FORECAST CONVECTIVE TEMPERATURE IS VERY HIGH AND DO
NOT THINK WE WILL BE ABLE TO GENERATE A LOWER CIG. SOUTH WINDS ARE
FORECAST TO PREVAIL WITH SUSTAINED SPEEDS OF 10 TO 15 KTS AND
GUSTS NEAR OR AROUND 20 KT FORECAST AT MOST OF THE TERMINALS.

WE ARE NOT CONFIDENT ABOUT THUNDER OCCURRING BECAUSE THE FORECAST
MODELS ARE PRESENTLY WAY OVERFORECASTING THE DEW POINTS WHICH IN
TURN INFLATES THE THUNDERSTORM POTENTIAL. WE CONTINUED WITH WHAT
OUR PRECEDING SHORT TERM MET DID WITH KPHL AND CARRY A CHANCE OF
SHRAS LATE IN THE TAF PERIOD ALL TERMINALS. THE HIGHER INTO THE
60S THE DEW POINTS GET TOMORROW, THE GREATER THE CHANCE FOR
THUNDER TO OCCUR.

OUTLOOK...
WEDNESDAY NIGHT...MOSTLY VFR CONDITIONS. MVFR POSSIBLE WITH ANY
SHOWERS/THUNDERSTORMS EARLY.

THURSDAY-FRIDAY...MOSTLY VFR CONDITIONS.

SATURDAY-SUNDAY...MAINLY VFR CONDITIONS...POSSIBLE PERIODS OF MVFR
SATURDAY NIGHT. SHOWERS ALSO POSSIBLE
-- End Changed Discussion --

&&

.MARINE...
HIGH PRESSURE WILL MOVE OVER THE SERN CONUS TODAY AND THEN FURTHER
EWD OVER THE SERN COASTAL WATERS TONIGHT. AS A RESULT THE WIND
AND SEAS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA THRU THE NEAR
PERIOD.

WEDNESDAY...GUIDANCE INDICATES OUR COASTAL WATERS WILL REACH SCA
WIND GUSTS DURING THE DAYTIME WEDNESDAY WITH SEAS BUILDING TO 5
FT ON THE ATLC WATERS DURING THE AFTN GENERATED BY THE SLY FLOW
AHEAD OF AN APPROACHING WFRONT. FOR LOWER DE BAY THERE MAY BE A
PERIOD OF SCA WIND GUSTS WEDNESDAY BUT CONFIDENCE WAS NOT HIGH
ENOUGH AT THIS TIME TO INCLUDE THIS AS A HEADLINE.

AM STARTING THE SCA A BIT SOONER ON THE ATLC WATERS WEDNESDAY...
AROUND 12Z. WILL LEAVE IT TO THE MID SHIFT TO ISSUE FOR DE BAY.

OUTLOOK...
THE SMALL CRAFT ADVISORY WILL REMAIN IN EFFECT THROUGH WEDNESDAY
NIGHT AS SEAS WILL LIKELY REMAIN ABOVE 5 FEET AND WINDS COULD GUST
AROUND 25 KNOTS EARLY. HOWEVER, AFTER THE COLD FRONT MOVES
THROUGH, WINDS ARE EXPECTED TO DROP BELOW ADVISORY LEVELS THROUGH
FRIDAY NIGHT. SEAS MAY REMAIN AROUND 5 FEET INTO EARLY THURSDAY,
BUT NOT CONFIDENT ENOUGH TO EXTEND THE ADVISORY OUT ANOTHER DAY
YET. ONCE SEAS DROP BELOW 5 FEET, THEY WILL REMAIN SO THROUGH
FRIDAY NIGHT.

AS WE MOVE INTO THE WEEKEND, HIGH PRESSURE BUILDS TO OUR
NORTH/NORTHEAST, WHICH WILL PRESENT AN EAST/SOUTHEAST FETCH ACROSS
THE WATERS. WINDS COULD BEGIN APPROACHING SMALL CRAFT CONDITIONS
STARTING SATURDAY NIGHT AND SEAS COULD BEGIN INCREASING AS WELL
CLOSE TO 5 FEET BY SUNDAY.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 7 AM WEDNESDAY TO 8 AM EDT THURSDAY
     FOR ANZ450>455.

&&

$$
SYNOPSIS...ROBERTSON
NEAR TERM...DRAG/GIGI
SHORT TERM...DRAG
LONG TERM...ROBERTSON
AVIATION...GIGI/ROBERTSON
MARINE...DRAG/ROBERTSON