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000
FXUS61 KPHI 130156
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
956 PM EDT WED JUN 12 2013

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL MOVE THROUGH THE REGION WITH A COLD
FRONTAL PASSAGE THURSDAY AND THURSDAY NIGHT. HIGH PRESSURE WILL
BUILD BACK INTO THE REGION FOR A MAJORITY OF THE WEEKEND. ANOTHER
FRONTAL BOUNDARY WILL APPROACH THE REGION FOR MONDAY AND
TUESDAY.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
VERY LITTLE CHANGE TO THIS EVENINGS TEMPERATURES AND DEWPOINTS.
DROPPED THE WINDS A BIT AND BACKED THEM TO THE EAST MORESO, BUT
FOR THE MOST PART THEY ARE GOOD. DID INCREASE POPS THROUGH
TOMORROW MORNING IN-LUE OF THE SOME OF THE HIGHER RES GUIDANCE
SHOWING THE WAA INDUCED RAIN MAKING ITS WAY INTO THE REGION,
THOUGH IT FIRST WILL HAVE TO OVERCOME THE RATHER DRY LOW-LEVELS.

OTHERWISE, THE MAIN FOCUS IS THE PLACEMENT OF A WARM FRONT AND
THE INCOMING CONVECTIVE THREAT WITH IT. WE START WITH A WARM FRONT
DRAPED ACROSS OUR SOUTHERN AREAS, AND THIS BOUNDARY MAY SETTLE A
LITTLE BIT FARTHER SOUTHWARD FOR AWHILE TONIGHT. THERE IS LOW TO
MID LEVEL WAA ONGOING FROM THE WEST AND THIS ALONG WITH SOME
INCREASE IN THE FLOW WILL PUSH THE WARM FRONT NORTHWARD SOME LATE.
THIS BOUNDARY WILL PROBABLY NOT GET ALL THAT FAR NORTH THOUGH
TONIGHT AS THE SYSTEM EAST OF MAINE LOOKS SLOW TO SHIFT ALL THAT
FAR TO THE EAST. THE WAA SURGE INCOMING FROM THE SOUTHWEST WILL BE
AIDED BY A LOW-LEVEL JET INCREASING TO AROUND 50 KNOTS UP THE OHIO
VALLEY BY LATE TONIGHT.

A CONVECTIVE CLUSTER/MCS HAS DEVELOPED ACROSS THE OHIO VALLEY WITH
ANOTHER SYSTEM TO THE NORTHWEST...BASED ON TWO SEPARATE MID-LEVEL
IMPULSES. THE FIRST IMPULSE, OVER THE OHIO VALLEY, SHOULD CONTINUE
TO DIVE SOUTHWARD AND INTO VIRGINIA. THE SECOND IMPULSE IS STILL
IN QUESTION TO WHERE IT WILL ULTIMATELY TRACK AND THUS HOW THE
SURFACE LOW PRESSURE WILL MOVE THROUGH THE MORNING HOURS.

AS FOR LOW TEMPERATURES, WE USED A GFS/NAM MOS BLEND. THE HOURLY
TEMPERATURE GRIDS HAD SOME INCORPORATION OF THE LAMP/LAV GUIDANCE TO
HELP WITH TRENDS THUS FAR.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
A RATHER ACTIVE DAY IS ANTICIPATED WITH AN ELEVATED RISK OF SEVERE
THUNDERSTORMS FOR AT LEAST PORTIONS OF THE CWA ALONG WITH ANOTHER
FLOODING THREAT. FOR MORE DETAILS REGARDING THE HEAVY RAIN/FLOODING
THREAT, SEE THE HYDROLOGY SECTION BELOW. THE EVOLUTION OF THE SEVERE
WEATHER THREAT THURSDAY MAY ULTIMATELY DEPEND ON THE DEVELOPMENT AND
BEHAVIOR OF AN MCS THROUGH TONIGHT /WEDNESDAY NIGHT/ INTO THE OHIO
VALLEY.

A STRONG SHORT WAVE TROUGH WILL BE APPROACHING OUR AREA FROM THE
WEST. THIS WILL DRIVE A STRENGTHENING SURFACE LOW EASTWARD, WITH IT
TRACKING RIGHT AROUND OUR CWA. WELL AHEAD OF THIS, THERE SHOULD BE
SOME SHOWERS AND PERHAPS SOME EMBEDDED THUNDER IN THE MORNING OWING
TO WAA AND INCREASING LIFT NORTH OF THE WARM FRONT. AN AREA OF RAIN
SHOULD CONTINUE TO ORGANIZE ACROSS THE NORTHERN ZONES AS THE LARGE
SCALE LIFT STRENGTHENS WITHIN A WAA REGIME AND NORTH OF A WARM FRONT.

AS THE SURFACE LOW ARRIVES IN THE AFTERNOON, A STRONG MID LEVEL JET
IS FORECAST TO BE ROUNDING THE BASE OF THE UPPER-LEVEL TROUGH. WHILE
THERE IS SOME VARIATIONS AMONG THE GUIDANCE REGARDING THE STRENGTH,
OVERALL A CORRIDOR OF MID LEVEL WINDS ON THE ORDER OF 60 KNOTS
LOOKS TO SLIDE ACROSS THE WARM SECTOR AND EVEN CROSS THE SURFACE
WARM FRONT. THIS WIND COMBINED WITH 30-40 KNOTS OF FLOW AT 850 MB
WILL SET UP A HIGH SHEAR ENVIRONMENT. WE TOOK A LOOK AT SOME POINT
FORECASTS FROM SOUTH TO NORTH, AND THESE SHOW QUITE A BIT OF SHEAR
TO SUPPORT THE DEVELOPMENT AND SUSTAINING OF ROTATING UPDRAFTS. THE
QUESTION THEN BECOMES HOW MUCH INSTABILITY IS REALIZED. AREAS SOUTH
OF THE WARM FRONT SHOULD BE ABLE TO HAVE ENOUGH BREAKS OF SUNSHINE
TO ALLOW DECENT INSTABILITY TO DEVELOP. THIS COMBINED WITH THE SHEAR
WILL BE SUPPORTIVE FOR SOME SUPERCELLS. AS ONE GOES NORTHWARD, WE
WILL HAVE TO WATCH ANY CONVECTIVE ELEMENTS THAT INTERSECT THE WARM
FRONT AS THE LOW-LEVEL SHEAR WILL BE THE GREATEST HERE. AND THEN
FARTHER NORTH, INSTABILITY SHOULD TREND DOWNWARD BUT BE MORE
ELEVATED DUE TO MORE WIDESPREAD PRECIPITATION ANTICIPATED. OUR
NORTHERN ZONES MAY HAVE LITTLE THUNDER DUE TO THIS, WITH THE MAIN
CONVECTIVE THREAT ALONG AND SOUTH OF THE WARM FRONT.

WHERE THIS WARM FRONT SETS UP WILL BE CRITICAL FOR THE PLACEMENT OF
CONVECTION AND IN PARTICULAR THE GREATEST TORNADO THREAT.
THUNDERSTORMS THAT DEVELOP ALONG AND SOUTH OF THE WARM FRONT WILL
HAVE THE POTENTIAL TO PRODUCE LARGE HAIL AND DAMAGING WINDS GIVEN
THE AMOUNT OF SHEAR FORECAST TO BE IN PLACE. IN ADDITION, THE
FORECAST SHEAR PROFILES WILL SUPPORT A TORNADO THREAT MAINLY JUST
AHEAD OF THE SURFACE LOW AND NEAR AND ALONG THE WARM FRONT WHERE
LOW-LEVEL SHEAR/HELICITY WILL BE MAXIMIZED. A POSSIBLE NEGATIVE
REGARDING TORNADOES IS THE HIGHER LCL HEIGHTS THAT ARE FORECAST BY
SOME OF THE GUIDANCE, ALTHOUGH THIS COULD END UP BEING LOWER
ESPECIALLY NEAR THE WARM FRONT AS MOISTURE COULD POOL MORE. IT IS
POSSIBLE THOUGH GIVEN THE SHEAR MAGNITUDE, THAT UPDRAFTS MAY
ORGANIZE INTO A LINE OR CONVECTIVE CLUSTER WITH POTENTIALLY DAMAGING
DOWNBURST WINDS. FARTHER SOUTH ACROSS MARYLAND AND DELAWARE, THE
WARM SECTOR WILL ALLOW THE SURFACE WINDS TO BE MORE SOUTHWESTERLY,
WHICH WILL TEND TO LIMIT THE LOW-LEVEL SHEAR. THE MODEL GUIDANCE
APPEARS TO BE A BIT FASTER WITH THE SURFACE LOW, AND THIS COULD BE
IN RESPONSE TO A MID LEVEL FEATURE SLIDING EAST-SOUTHEASTWARD FROM
WHATEVER CONVECTIVE COMPLEX ORGANIZES WELL TO OUR WEST WEDNESDAY
NIGHT. THIS COULD IMPACT THE TRACK OF THE SURFACE LOW TO SOME
DEGREE. WE INCLUDED THE MENTION OF DAMAGING WINDS IN THE FORECAST
FOR MUCH OF THE AREA AS A RESULT.

WE MAINTAINED THE HIGHEST POPS ACROSS THE NORTH AND THOUGHT ABOUT
CHANGING THE SHOWERS TO RAIN, BUT DECIDED TO KEEP IN SIMPLE DUE TO A
MORE OF A CONVECTIVE ASPECT FARTHER TO THE SOUTH. AS FOR
TEMPERATURES, WE MOSTLY TOOK AN EVEN NAM/GFS MOS BLEND AND THIS
GENERALLY SHOWS THE GRADIENT FROM SOUTH TO NORTH DUE TO THE WARM
SECTOR PROBABLY NOT GETTING TO OUR NORTHERN ZONES.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
THURSDAY NIGHT: HIGH IMPACT SYSTEM CONTINUES

SEVERE: CONVECTION BY THE EVENING SHOULD EVOLVE INTO A CLUSTER(S)
OR A SQUALL LINE DUE TO THE AMPLE AMOUNTS OF SHEAR HAVE CARRIED OVER
WORDING FROM SHORT TERM PORTION OF FORECAST INTO THE EVENING
GRIDS. MORE DETAILS ON THE SEVERE THREAT CAN BE FOUND ON THE SPC
OUTLOOKS AND THE SHORT TERM PART OF THE AFD.

WIND:
WINDS MAY INCREASE OUT OF THE NORTH FROM 15-25 KNOTS SUSTAINED FOR A
PERIOD THURSDAY NIGHT WITH HIGHER GUSTS. THE LATEST 12Z MODEL SUITE
IS A TOUCH WEAKER WITH THE LOW PRESSURE SYSTEM AND THUS THE OVERALL WIND
FIELD IS LESS IMPRESSIVE. THROUGH A MOMENTUM TRANSFER ANALYSIS COULD
SEE SOME GUSTS FROM 25-30 KNOTS REACHING THE SURFACE AT TIMES. ATTM
THIS IS FORECASTED BELOW WIND ADVISORY CRITERIA.

QPF: WENT WITH A BLEND OF WPC AND SREF QPF. THOUGHT JUST WPC
WAS TO LOW AND THE RFC WAS ON THE HIGHER END FOR THE THURSDAY NIGHT
PERIOD.

REST OF EXTENDED:

THIS LOW PRESSURE SYSTEM DEPARTS THE REGION ON FRIDAY. STILL WILL
HANG ONTO A LOW CHANCE FOR SHOWERS THROUGH THE DAY ON THE BACKSIDE
OF THE LOW. CLOUDS MAY KEEP TEMPERATURES DOWN WITH A NORTHERLY FLOW.
WENT WITH A SLOW CLEARING FOR THE FRIDAY NIGHT PERIOD. LEADING TO A
QUIET SATURDAY. WENT SLIGHTLY ABOVE GUIDANCE ON WINDS FOR FRIDAY
THINKING THE STORM MAY STILL LEAD TO HIGHER GUSTS THAN TRADITIONAL
RULES OF THUMB. DID GO SLIGHTLY WARMER THAN RAW MODEL GUIDANCE WITH
TEMPERATURES ON SATURDAY.

THE 12Z GFS BRINGS IN THE NEXT SYSTEM SUNDAY. FEEL THIS MAY BE A
TOUCH TO FAST AND HAVE HELD OFF RAIN AND THUNDER CHANCES TILL SUNDAY
NIGHT. A FRONTAL BOUNDARY WILL MOVE INTO THE REGION FOR MONDAY AND
TUESDAY, AS USUAL THE EXACT TIMING IS IN QUESTION. THE 12Z ECMWF IS
ALSO DRIER FOCUSING THUNDERSTORMS TO OUR SOUTH. HAVE LEFT IN CHANCE
POPS FOR NOW DUE TO THE UNCERTAINTY. THIS FRONTAL BOUNDARY GIVES WAY
TO HIGH PRESSURE FOR WEDNESDAY. OVERALL IT APPEARS LIMITED SHEAR MAY
PREVENT A THREAT FOR STRONG STORMS WITH THE FRONTAL PASSAGE ATTM.
AFTER SATURDAY DID NOT STRAY MUCH FROM GUIDANCE WITH MOST WEATHER
ELEMENTS.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

TONIGHT...MOSTLY VFR. THE START OF A VERY COMPLEX FORECAST WHICH
GREATLY DEPENDS ON THE LOCATION OF A SURFACE WARM FRONT AND LOW
PRESSURE SYSTEM. MOST TERMINALS WILL START A LIGHT NORTHERLY WIND
THAT MAY GO VARIABLE FOR A TIME BUT ULTIMATELY TURN TOWARDS THE
EAST-SOUTHEAST AHEAD OF THE APPROACHING WARM FRONT AND LOW
PRESSURE SYSTEM. SOME SHOWERS SHOULD DEVELOP MAINLY LATE TONIGHT WHICH
WE CONTINUE IN THE FORECAST ALTHOUGH WE BACKED OFF ANY VSBY
RESTRICTIONS. ALTHOUGH THE THUNDER POTENTIAL IS SOMEWHAT
UNCERTAIN SO WE OPTED TO NOT INCLUDE IT.

THURSDAY...MVFR /LOCAL IFR POSSIBLE AT TIME/ WITH SHOWERS AND
THUNDERSTORMS ON THE INCREASE. SOME OF THE RAIN CAN BE LOCALLY HEAVY
WITH GREATLY REDUCED VISIBILITIES, AND THUNDERSTORMS MAY PRODUCE
LOCALLY STRONG WIND GUSTS. EAST-SOUTHEAST WINDS 5-10 KNOTS, THEN
BECOMING MORE SOUTH-SOUTHWEST ESPECIALLY FROM THE KPHL METRO SOUTH
WITH SOME INCREASE AND GUSTS INTO THE LOW-20S. WITH THE WESTWARD
WIND SHIFT CIGS SHOULD BE ABLE TO SCATTER OUT TO VFR. STILL A
LOW CONFIDENCE FORECAST ON WINDS AND CIGS.

OUTLOOK....

THURSDAY NIGHT: MVFR TO IFR CONDITIONS RAIN AT ALL TAF SITES WITH
THUNDERSTORMS FROM PHL AND TTN SOUTH. NORTHEAST WINDS FROM 15 TO 20
KNOTS WILL SHIFT TO THE NORTHWEST WITH HIGHER GUSTS.

FRIDAY: IMPROVING CONDITIONS TO VFR THROUGHOUT THE DAY WITH ISOLATED
SHOWERS. WINDS NORTHWEST AT 15 KNOTS WITH HIGHER GUSTS.

SATURDAY AND SUNDAY: VFR WITH SUNNY SKIES, WINDS WEST TO SOUTHWEST
AROUND 5 KNOTS.

SUNDAY NIGHT AND MONDAY: VFR TO MFVR WITH PASSING SHOWERS AND PERHAPS SOME
THUNDER.

&&

.MARINE...
THE CONDITIONS ARE FORECAST TO BE BELOW SMALL CRAFT ADVISORY INTO
THURSDAY. WEST-NORTHWEST WINDS DIMINISHING SOME THROUGH TONIGHT AND
TURNING SOUTHEAST. A WARM FRONT WILL BE NEARBY THROUGH THURSDAY. AN
AREA OF LOW PRESSURE WILL TRACK EASTWARD AND CROSS OVER OUR AREA
DURING THE DAY THURSDAY. AN INCREASING WIND FIELD IS FORECAST TO
ACCOMPANY THIS WITH THE SOUTHERN WATERS GETTING INTO THE WARM
SECTOR. IT IS HERE WHERE THE WINDS MAY INCREASE MORE COMPARED TO
FARTHER NORTH, ALTHOUGH SOUNDINGS INDICATE A SHARP INVERSION NOT TO
FAR ABOVE THE SURFACE WHICH WILL HELP TO LIMIT MIXING FOR AWHILE.
GIVEN THE WIND FORECAST IN THE BOUNDARY LAYER, WE OPTED TO ISSUE A
SMALL CRAFT ADVISORY STARTING AT 16Z THURSDAY FOR ALL BUT THE UPPER
DELAWARE BAY. OUR CONFIDENCE IN THE UPPER BAY IS LOW REGARDING HOW
MUCH MIXING CAN OCCUR AND EVEN THE LOWER BAY COULD BE MARGINAL
REGARDING THE ADVISORY. ON THE OCEAN, THE SEAS ARE FORECAST TO BUILD
TO AROUND 5 FEET THURSDAY.

OUTLOOK...
SEAS AND WINDS WILL MEET SCA CRITERIA THROUGH 00Z SATURDAY. WINDS
MAY APPROACH GALES FOR A TIME PERIOD LATE THURSDAY NIGHT AND EARLY
FRIDAY. HOWEVER DO NOT THINK GALE CONDITIONS WILL BE MET ATTM.
CONDITIONS SHOULD REMAIN BELOW SCA CRITERIA THROUGH THE REMAINDER OF
THE WEEKEND AND MONDAY.

&&

.HYDROLOGY...
FLOOD WATCH REMAINS IN EFFECT FOR THURSDAY INTO FRIDAY MORNING.

ANOTHER ROUND OF HEAVY RAIN LOOKS LIKELY THURSDAY ACROSS AT LEAST
ABOUT THE NORTHERN HALF OF OUR FORECAST AREA. A STRENGTHENING
SURFACE LOW WILL SLIDE ACROSS OUR AREA WITH A NORTHWARD BOUND WARM
FRONT. THE WARM FRONT LOOKS TO GET HUNG UP NEAR OUR CENTRAL ZONES,
SETTING THE STAGE FOR A HEAVY RAIN EVENT. MOST OF THE INTERSTATE 95
CORRIDOR HAS PICKED UP 4 TO 6 INCHES OF RAIN OVER THE PAST WEEK. AS
ANOTHER ROUND OF HEAVY RAIN TAKES AIM ON OUR AREA COMBINED WITH
SATURATED SOILS WITH ALREADY HIGHER LEVELS IN THE RIVERS AND
STREAMS, IT WILL NOT TAKE AS MUCH ADDITIONAL RAINFALL TO PRODUCE
RENEWED FLOODING.

THE PW VALUES ARE FORECAST TO INCREASE TO NEAR 2 INCHES DURING
THURSDAY AS WAA ALOFT COMBINED WITH LOW-LEVEL CONVERGENCE NEAR THE
WARM FRONT TAKES PLACE. THIS SHOULD RESULT IN ENHANCED RAINFALL
RATES, AND THEREFORE THERE IS ANOTHER ROUND OF FLOOD AND/OR FLASH
FLOOD POTENTIAL ACROSS A GOOD PART OF OUR REGION. IT APPEARS THAT
2 TO 4 INCHES OF RAIN FALLS ACROSS THE AREA, HOWEVER LOCALLY HIGHER
AMOUNTS ARE POSSIBLE WITH THE HEAVIEST ACROSS OUR NORTHERN AREAS. A
PARTICULAR CONCERN IS NORTHERN NEW JERSEY AS THE HEAVIEST RAIN MAY
BE CENTERED HERE OR VERY NEAR HERE. THE CONSENSUS OF THE GUIDANCE
POINTS TO THE HIGHEST RAINFALL AMOUNTS AND LARGER AREAL COVERAGE
ACROSS ABOUT THE NORTHERN HALF OF THE CWA. IN ADDITION, THE MAIN
AXIS OF HEAVY RAIN MAY FALL IN SOUTHEASTERN NEW YORK STATE, WHICH
THE ASSOCIATED RUNOFF WILL DRAIN INTO THE DELAWARE RIVER. THEREFORE,
SIGNIFICANT RISES, TO NEAR BANKFULL, ARE ALSO ANTICIPATED ON THE
DELAWARE RIVER. OVERALL, THE FLOOD WATCH REMAINS IN EFFECT AS IS
WITH THE GREATEST RISK OF FLOODING ACROSS THE NORTH AND ALONG THE
INTERSTATE 95 CORRIDOR. SOUTH OF THE WATCH AREA, LOCALLY HEAVY RAIN
SHOULD OCCUR HOWEVER THIS SHOULD BE MANLY CONVECTIVE AS THE MAIN
OVERRUNNING RAIN STAYS TO THE NORTH ALONG WITH FAST ENOUGH STORM
MOTIONS.

&&

.RIP CURRENTS...
A MODERATE RISK OF RIP CURRENTS REMAINS IN EFFECT IN NJ TODAY.

&&

.CLIMATE...
JUNE RECORD MONTHLY RAINFALL...

PHL...10.06 INCHES IN 1938. 6.79 INCHES...RANKED 10TH.  POR 1872
ILG....9.90 INCHES IN 2003. 7.13 INCHES...RANKED 7TH.   POR 1894
ACY....8.45 INCHES IN 1920. 4.07 INCHES...NOT TOP 10.   POR 1874
ABE....FORTHCOMING IN 1938. 4.55 INCHES.................POR 1922
GED....14.07 INCHS IN 2006. 8.51 INCHES. POR VERY SHORT
TTN....13.80 INCHS IN 1996. 5.99 INCHES. POR 1865
RDG....15.73 INCHS IN 1972. 4.17 INCHES. POR 1869
MPO....12.10 INCHS IN 2006. 5.12 INCHES. POR 1901

THURSDAY JUNE 13TH DAILY RECORD RAINFALL...

ACY...1.29 INCHES IN 1953.
TTN...1.70 INCHES IN 1982.
PHL...2.21 INCHES IN 1982.
ILG...2.41 INCHES IN 1982.
GED...2.10 INCHES IN 1962.
ABE...2.93 INCHES IN 1942.
RDG...1.19 INCHES IN 1936.
MPO...1.76 INCHES IN 1936.

RAINFALL THIS MONTH IN OUR AREA, THROUGH THE 10TH, IS ABOUT 200-400
PERCENT OF NORMAL WITH 5 TO 7 INCHES COMMON ALONG THE I-95 CORRIDOR.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FLOOD WATCH FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT
     FOR PAZ054-055-060>062-070-071-101>106.
NJ...FLOOD WATCH FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT
     FOR NJZ001-007>010-012>020-026-027.
DE...FLOOD WATCH FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT
     FOR DEZ001.
MD...FLOOD WATCH FROM THURSDAY MORNING THROUGH LATE THURSDAY NIGHT
     FOR MDZ008.
MARINE...SMALL CRAFT ADVISORY FROM NOON THURSDAY TO 8 PM EDT FRIDAY FOR
     ANZ450>455.
     SMALL CRAFT ADVISORY FROM NOON TO 6 PM EDT THURSDAY FOR ANZ431.

&&

$$
SYNOPSIS...GAINES/NIERENBERG
NEAR TERM...GORSE/HEAVENER
SHORT TERM...GORSE
LONG TERM...GAINES/NIERENBERG
AVIATION...GAINES/GORSE/HEAVENER/NIERENBERG
MARINE...GAINES/GORSE/NIERENBERG
HYDROLOGY...
RIP CURRENTS...
CLIMATE...