481
FXUS61 KPHI 240230
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1030 PM EDT WED JUL 23 2008
SYNOPSIS
A LOW PRESSURE SYSTEM OVER THE EASTERN GREAT LAKES WILL MOVE INTO
THE SAINT LAWRENCE RIVER VALLEY TONIGHT. ITS COLD FRONT SHOULD MOVE
THROUGH THE REGION ON THURSDAY AND SLOWLY OFFSHORE THURSDAY NIGHT.
WEAK HIGH PRESSURE WILL THEN BUILD EAST INTO THE AREA ON FRIDAY AND
SATURDAY BEFORE MOVING OFFSHORE. A SLOW MOVING COLD FRONT IS THEN
FORECAST TO CROSS THE APPALACHIANS AND THE ATLANTIC SEABOARD ON
SUNDAY AND MONDAY BEFORE STALLING JUST OFFSHORE ON TUESDAY AND
WEDNESDAY.
NEAR TERM /THROUGH THURSDAY/
PUBLIC PRODUCTS ISSUED TO CANCEL THE SEVERE THUNDERSTORM WATCH.
THE GFS INITIALIZATION OF THE H5 TROF WAS SLIGHTLY BETTER THAN THE
WRF-NMM. BOTH MODELS LOOKED DECENT AT 850MB AND 925MB. FROM THERE
THE GFS AND WRF-NMM GO QUICKLY THEIR SEPARATE WAYS WITH THE WRF-NMM
SOLUTION MUCH SLOWER THAN ANY OF THE OTHER MODELS. BASED ON COLLAB
WITH HPC AND THE WRF-NMM ALREADY TOO SLOW, THE TENDENCY FOR NEG TILT
SYSTEMS TO BE FASTER, THIS FCST PACKAGE SIDES CLOSER TO THE GFS.
ONTO THE HEAVY RAIN POTENTIAL ONCE A TROF GOES NEGATIVE, IT BECOMES
A VERY EFFICIENT PCPN PRODUCER. THIS IS FAIRLY ANOMALOUS FOR JULY VS
NOVEMBER. THE GFS HAS BACKED AWAY CONSIDERABLY FROM ITS FORECAST
LLVL JET FROM PREVIOUS RUNS, FORMING IT TOO LATE FOR US. MEANWHILE
THE WRF-NMM PRODUCES COPIOUS AMOUNTS OF NON-CONVECTIVE RAIN. THE GFS
IF ANY TENDENCY SOMETIMES IS TOO EAST WITH HVY RAIN BANDS, SO
THINKING THE SECOND PRONGED APPROACH MIGHT BE TOO FAR EAST, OR TO
PUT IT ANOTHER WAY CONFIDENCE IS NOT HIGH ENOUGH TO BELIEVE THAT
WILL MISS US TO THE EAST GIVEN THE LOCATION OF THE H2.5 JET. THE
DECREASE IN LLVL WINDS REDUCES THE CHANCES OF BACKWARD PROPAGATING
TSRAS. NEVERTHELESS TRAINING IS LIKELY GIVEN THE SLOW EWD
PROPAGATION OF PCPN BANDS BEFORE THE TROF GOES NEGATIVE TILT. THIS
WOULD FAVOR IF ONE WOULD CALL IT THAT OUR PA CWA AS THE MOST LIKELY
AREA TO SEE THE HEAVIEST RAIN AND TRAINING, ANOTHER AS MY COLLEAGUE
HAS SAID FALL LINE EVENT?
BY THE WAY ITS BEEN SO DRY FOR SO LONG AND THE NYC RESERVOIRS ARE
WELL BELOW CAPACITY THAT IS MORE A SMALLER STREAM, FASTER RESPONDING
CONCERN THAN MAIN STEM RIVERS.
SHORT TERM /THURSDAY NIGHT/
CHANGE FROM PREVIOUS PACKAGE WAS TO END THE FFA A BIT SOONER AS THE
GFS HAS THE HEAVIEST RAIN OVER BY NOON AND THE CAN RGEM GOES AS FAR
AS HAVE ALL RAIN DONE BEFORE 8 AM. THE WRF-NMM APPEARS TO REMAIN THE
SLOWEST OUTLIER AND MOST NEGATIVE TILT PCPN EVENTS DO NOT DRAG. BY
THE TIME THE HEAVY PRECIP BAND REACHES NJ AND DE, THE TROF SHOULD BE
NEGATIVE. WHILE THE PRECIP SHOULD BE HEAVY, IT SHOULD NOT HAVE THE
LAGGING LOOK THAT THE WRF-NMM HAS. THERE ARE STILL SOME SHORT WAVES
ROTATING THROUGH AND WE DID NOT WANT TO END ALL CHANCES PRIOR TO
NOON. GFS MOS MAX TEMPS LOOK BETTER AS WE ARE EXPECTING SOME
SUNSHINE TO RETURN DURG THE AFTN, ESP SWRN ZONES.
SKIES SHOULD CLEAR ALL AREAS BY THURSDAY NIGHT AND PENDING THE
AMOUNT OF PCPN THAT DOES FALL, SOME PATCHY FOG MIGHT BE NEEDED TO BE
ADDED IN THE ZONES. THERE ARE SOME SHORT WAVES FCST TO MOVE THROUGH
OUR CWA ON FRIDAY, BUT HEIGHTS ARE FCST TO AND FCST SOUNDINGS LOOKED
CAP. WE WILL CONTINUE THE DRY FORECAST. ASSUMING WE GET THE HEAVY
RAIN, MORE ENERGY SHOULD GO TOWARD EVAPORATING THE WATER VS HEATING
THE GROUND AND WE SUSPECT GFS MOS MAY BE TOO WARM FOR THIS REASON IF
EVERYTHING GOES ACCORDING TO PLAN.
LONG TERM /FRIDAY THROUGH WEDNESDAY/
MORE PRECIPITATION CHANCES ARE IN THE OFFING AS WELL AS TEMPS THAT
SHOULD AVERAGE CLOSE TO NORMAL AS THE GENERAL LONG WAVE PATTERN WILL
SUPPORT TROFFING OVER THE EASTERN CONUS. THERE IS A LARGER THAN
USUAL MODEL SPREAD WITH RESPECT TO TIMING AND WE GET INTO SOME
PROBABLY SPURIOUS CONVECTIVE FEEDBACK SYSTEMS TOWARD THE END OF THE
PERIOD. SO WHILE CONFIDENCE IS HIGH ABOUT THE PATTERN EVOLVING, ITS
NOT AS HIGH WRT TO THE INDIVIDUAL DAILY DETAILS.
GREATEST CONFIDENCE AS WELL AS BEST MODEL CONSENSUS IS FOR
PRECIPITATION CHANCES WITH THE NEXT COLD FRONT LATER ON SATURDAY
INTO SATURDAY NIGHT AND SUNDAY. WE WILL CARRY THE HIGHEST POPS OF
THE EXTENDED PERIOD WITH THIS SYSTEM. COULD BE ANOTHER CHAMBER OF
COMMERCE ADJUSTMENT (LIKE TODAY) FOR SHORE AND SERN CWA AREAS
SATURDAY AS THE FRONT WILL BE FAIRLY FAR TO THE WEST. FOR NOW WE
ADJUSTED THE POP GRADIENT TO REFLECT THIS WITH THE HIGHEST POPS FAR
NW AND LOWEST SE.
SUNDAY'S PCPN CHANCES COULD BE ONE OF THOSE RIGHT FOR THE WRONG
REASONS EVENTS OCCURRING EITHER BECAUSE THE FRONT WILL BE SLOWER OR
FROM SHORT WAVES PASSING THROUGH THE CYCLONIC FLOW ALOFT. FOR THE
REST OF THE EXTENDED THERE IS REDUCED CONFIDENCE AS TO HOW FAR SOUTH
THE FRONT WILL BE ABLE TO GET AND HOW WAVES ALONG THE FRONT OR JUST
SHORT WAVES IN THE CYCLONIC FLOW ALOFT WILL AFFECT US. THERE IS ALSO
A BIG TIMING DIFFERENCE ALONG THE NORTHERN TIER OF THE CONUS BETWEEN
THE ECMWF AND OTHER MODELS THAT HOPEFULLY WILL BE NARROWED IN THE
DAYS TO COME. WE DID NOT DIFFER MUCH WITH MOS GUIDANCE BEYOND
SATURDAY AND THE ECMWF LOOKS LIKE IT STILL HAS ITS WARM BIAS OVER
OUR CWA INTACT.
AVIATION /03Z THURSDAY THROUGH MONDAY/
SHOWERS AND THUNDERSTORMS ARE DEVELOPING ACROSS PARTS OF THE AREA
THIS AFTERNOON, AHEAD OF AN EXTENSIVE AREA OF RAIN THAT IS IN OUR
WESTERN PORTIONS OF THE CWA. THESE SHOWERS AND THUNDERSTORMS WILL
LAST THROUGH THE EVENING, AND THE RAIN WILL CONTINUE TO MOVE
EASTWARD AND REMAIN MOST OF THE NIGHT UNTIL THE FRONT PASSES THROUGH
TOWARD MORNING; THE SHOWERS SHOULD THEN TAPER OFF AS WE GO THROUGH
THE DAY TOMORROW. THE VSBYS AND CIGS WILL LIKELY COME DOWN TO MVFR
ONCE THE RAIN BEGINS IN ALL AREAS THIS EVENING AND REMAIN SO THROUGH
MOST OF THE NIGHT. WINDS WILL BE TRICKY THIS EVENING DUE TO THE
FRONTAL BOUNDARY THAT IS DRAPED ACROSS THE AREA, AS WELL AS THE
DEVELOPING THUNDERSTORMS AS THEY COULD PRODUCE SOME OUTFLOW
BOUNDARIES ACROSS THE AREA. THE BOUNDARY IS SLOWLY MOVING NORTHWARD,
AND AS IT DOES SO, THE WINDS WILL SLOWLY VEER BACK TO MORE OF A
SOUTHERLY DIRECTION. HAVE DECIDED TO KEEP EVERYONE SOUTHEASTERLY
THROUGH MUCH OF THE EVENING, THEN SOUTHWESTERLY OVERNIGHT. AFTER THE
FRONT PASSES THROUGH TOMORROW, WINDS WILL LIKELY GO WESTERLY.
OUTLOOK...SHOWERS AND TSTMS SHOULD END BY LATE IN THE DAY ON
THURSDAY AND WE SHOULD SEE FAIR CONDITIONS THROUGH FRIDAY. THERE MAY
BE A CHANCE OF SHOWERS AND THUNDERSTORMS AS WE GO INTO THE WEEKEND,
WHICH COULD LOWER CIGS AND VSBYS IF THEY OCCUR.
MARINE
EVEN THOUGH THE BUOYS ARE NOT REACHING SMALL CRAFT CRITERIA AT THIS
MOMENT, THE WINDS ARE BEGINNING TO INCREASE AND SHOULD CONTINUE
THROUGH THE EVENING. A GENERAL SOUTHERLY TO SOUTHWESTERLY FLOW
SHOULD REMAIN ACROSS THE WATERS OVER THE NEXT SEVERAL DAYS. SEAS
SHOULD INCREASE TONIGHT, AND LAST THROUGH THE DAY ON THURSDAY, AND
BEGIN TO SLACK THURSDAY NIGHT INTO FRIDAY. THEREFORE, WE WILL EXTEND
THE SMALL CRAFT ADVISORY THROUGH THE DAY ON THURSDAY. AN APPROACHING
FRONTAL SYSTEM WILL BRING SHOWERS AND TSTMS TO THE AREA THROUGH
OVERNIGHT TONIGHT AND LAST THROUGH THE DAY ON THURSDAY WITH LOCALLY
GUSTY WINDS AND VERY HEAVY RAINFALL. HIGH PRESSURE IS FORECAST TO
BUILD ACROSS THE AREA FRIDAY AND THEN MOVE OFFSHORE THIS WEEKEND,
BEFORE A COLD FRONT MOVES THROUGH THE AREA ON SUNDAY. THEREFORE,
SHOWERS AND THUNDERSTORMS ARE POSSIBLE FOR SATURDAY INTO SUNDAY.
WINDS AND WAVES MAY INCREASE SLIGHTLY AS THIS FRONT MOVES THROUGH
THE AREA, BUT IT IS HARD TO SAY AT THIS TIME IF THEY WILL REACH
SMALL CRAFT CRITERIA AT THIS POINT OR NOT.
PHI WATCHES/WARNINGS/ADVISORIES
PA...FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR PAZ054-055-
060>062-067>071.
NJ...FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR NJZ001-007>010-
012>027.
DE...FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR DEZ001>004.
MD...FLASH FLOOD WATCH THROUGH THURSDAY MORNING FOR MDZ008-012-015-
019-020.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THURSDAY FOR ANZ450>455.
SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY FOR ANZ431.
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
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