623
FXUS61 KPHI 241922
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
322 PM EDT THU JUL 24 2008
SYNOPSIS
AN AREA OF LOW PRESSURE IN SOUTHEASTERN CANADA WILL PUSH A COLD
FRONT EAST OF OUR ENTIRE AREA THIS EVENING. HIGH PRESSURE WILL
THEN GRADUALLY SETTLE INTO OUR AREA TONIGHT AND FRIDAY, BEFORE
SLIDING TO OUR EAST FRIDAY NIGHT INTO SATURDAY. A COLD FRONT IS
THEN FORECAST TO ARRIVE ON SUNDAY, THEN POTENTIALLY STALL TO OUR
SOUTH AND EAST NEXT WEEK AS A FEW LOW PRESSURE SYSTEMS POSSIBLY
TRAVEL ALONG IT.
NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
A PUBLIC INFORMATION STATEMENT /PNS/ WAS ISSUED EARLIER,
CONTAINING RAINFALL TOTALS OF THE RECENT EVENT.
A SURFACE ANALYSIS THIS AFTERNOON SHOWS A LOW PRESSURE SYSTEM IN
SOUTHEASTERN CANADA WITH A COLD FRONT STRETCHED FROM EASTERN NEW
YORK STATE, SOUTHWARD ACROSS NEW JERSEY AND THEN INTO THE
CAROLINAS. AN UPPER AIR ANALYSIS INDICATES A RATHER IMPRESSIVE
TROUGH FOR THIS TIME OF THE YEAR ACROSS THE EASTERN GREAT LAKES
DOWN INTO THE MID ATLANTIC. A POTENT 300 MB JET IS FOUND ON THE
WEST AND ALSO EAST SIDES OF THIS UPPER TROUGH, WITH SOME SHORT
WAVE ENERGY ROTATING AROUND IT. THE WATER VAPOR IMAGERY THIS
AFTERNOON SHOWS THE UPPER LOW NICELY ACROSS CENTRAL NEW YORK WITH
VERY DRY MIDLEVEL AIR FROM EASTERN PENNSYLVANIA SOUTHWARD. THE
DRY AIR SEEMS TO HAVE KEPT A LID ON ANY RENEWED DEVELOPMENT BEHIND
THE COLD FRONT DESPITE THE PRESENCE OF THE SHARP UPPER-LEVEL
TROUGH.
THE COLD FRONT HAS BEEN VERY SLOWLY MOVING EASTWARD THIS AFTERNOON
AS IS NEARLY JUST EAST OF THE JERSEY SHORE ATTM. THE SURFACE DEW
POINTS HAVE BEEN GRADUALLY LOWERING IN ITS WAKE AS THE MUCH DRIER
AIR IS WORKING ITS WAY DOWNWARD. THE LATEST MODEL GUIDANCE IS NOT
TO IMPRESSED WITH CONVECTION DEVELOPING INTO THIS EVENING AND THIS
IS PROBABLY TIED TO OUR CWA IN BETWEEN THE MOIST PLUME /NOW JUST
OFF THE COAST/ AND THE COLDEST AIR ALOFT AND CONVERGENCE NEAR THE
UPPER-LEVEL LOW TO OUR NORTHWEST. THE ACTUAL UPPER-LEVEL LOW
APPEARS TO BE CENTERED IN WESTERN NEW YORK, AND THIS IS FORECAST
TO TRACK NORTHEASTWARD THROUGH THIS EVENING. THE TRAILING UPPER
TROUGH EXTENDS SOUTHWARD ACROSS WESTERN/CENTRAL PENNSYLVANIA AND
IS NEARLY COLLOCATED WITH THE 500 MB THERMAL TROUGH. AN AREA
OF MIDLEVEL DPVA IS FORECAST TO LIFT NORTHEASTWARD AND MAY SCRAPE
OUR FAR NORTHWESTERN COUNTIES. CONVECTION HAS DEVELOPED FROM
CENTRAL-WESTERN NEW YORK INTO THE NORTH-CENTRAL PENNSYLVANIA AREA
AND SOME OF THIS COULD PIVOT INTO OUR NORTHWEST ZONES THROUGH
EARLY EVENING. FOR NOW, WE JUST WENT WITH A SLIGHT CHC TO LOW CHC
POP TO INDICATE THIS ISOLATED TO PERHAPS SCATTERED POTENTIAL.
ELSEWHERE, WE DECIDED TO GO WITH A DRY FORECAST WITH THE EXCEPTION
OF LOW CHC POPS OVER PARTS OF THE COASTAL WATERS THIS EVENING AS
THE FRONTAL BOUNDARY IS CLOSE BY.
THE CUMULUS THAT DEVELOPED TODAY IN CONCERT WITH DAYTIME HEATING
AND RESIDUAL LOW-LEVEL MOISTURE WILL DISSIPATE THIS EVENING. THE
MAIN SHORT WAVE WILL BE PIVOTING JUST TO OUR NORTH TONIGHT AND
EARLY FRIDAY MORNING, HOWEVER IT APPEARS LITTLE IN THE WAY OF
CLOUDS WILL BE TOSSED OUR WAY FROM THAT. THEREFORE, A CLEARING SKY
IS EXPECTED THROUGH THE NIGHT. EVEN THOUGH THE AIRMASS IS DRYING,
GIVEN THE LACK OF CLOUDS EXPECTED OVERNIGHT, THE RECENT RAIN, AND
LIGHT WINDS, WE ADDED PATCHY FOG MAINLY IN THE LOW-LYING AREAS
OVERNIGHT.
AS FOR TEMPERATURES, WE LEANED A BIT MORE TOWARD THE GFS MOS AS THEY
FIT THE DEW POINT EXPECTATION A BIT BETTER. WE ALSO LEANED MORE
TOWARD GFS MOS REGARDING DEW POINTS ON FRIDAY AS FORECAST SOUNDINGS
INDICATE THAT MIXING OF DRIER AIR FROM ALOFT COULD MAKE IT TO THE
SURFACE.
SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/
HIGH PRESSURE AT THE SURFACE WILL BE BUILDING INTO THE AREA ON
FRIDAY AS THE AMPLIFIED UPPER-LEVEL TROUGH LIFTS OUT SOME. WE WILL
STILL BE UNDER SOME CYCLONIC FLOW, HOWEVER WITH THE UPPER TROUGH
BECOME LESS AMPLIFIED, OUR WIND DIRECTION AT THE SURFACE SHOULD BE
FROM THE WEST OR EVEN SOUTHWEST. THIS WILL ALLOW AFTERNOON
TEMPERATURES TO RISE WELL INTO THE 80S FOR MOST PLACES, AND THE WIND
IS NOT THAT STRONG IN THE BOUNDARY LAYER SO THE IMMEDIATE COASTAL
AREAS COULD SEE THE SURFACE WINDS BACK MORE TO THE SOUTH WITH
TIME. THE FORECAST SOUNDINGS INDICATE A GOOD AMOUNT OF DRY AIR
WITHIN THE ATMOSPHERIC COLUMN, THEREFORE NOT A LOT OF CLOUDS ARE
ANTICIPATED OTHER THAN JUST SOME CUMULUS DESPITE A SHORT WAVE
MOVING BY. THERE MAY BE CONVECTION IN THE GREAT LAKES TO THE
TENNESSEE VALLEY, WHICH MAY TOSS SOME HIGH-LEVEL CLOUDS OUR WAY
THOUGH, GIVEN THE FLOW, ON FRIDAY AND FRIDAY NIGHT.
THE SURFACE HIGH IS FORECAST TO SETTLE TO OUR EAST FRIDAY NIGHT WITH
A SOUTH TO SOUTHWEST FLOW ACROSS THE AREA. AFTER A BREAK FROM THE
HUMIDITY FRIDAY ACROSS NEARLY THE ENTIRE AREA, IT SHOULD BE ON THE
INCREASE AGAIN SATURDAY UNDER A RETURN FLOW AHEAD OF OUR NEXT
FRONTAL BOUNDARY. SOME WAA ALONG WITH SOME SHORT WAVE ENERGY
EMBEDDED WITH THE WEST-NORTHWESTERLY UPPER-LEVEL FLOW MAY BE ENOUGH
TO PRODUCE SOME CONVECTION TO OUR WEST SATURDAY. SOME OF THIS
ACTIVITY MAY MAKE A RUN AT OUR WESTERN COUNTIES IN THE AFTERNOON,
THEREFORE A SLIGHT CHC WAS PLACED IN THE GRIDS. THE GFS IS MORE
AGGRESSIVE IN AMPLIFYING THE UPPER TROUGH SATURDAY NIGHT WHILE THE
WRF-NMM KEEPS THE UPPER FLOW MORE ZONAL. AS A RESULT, THE GFS
INDICATES MORE CONVECTION SATURDAY NIGHT. THE SREF 6-HOUR
TOTAL PRECIPITATION MEAN IS HITTING THE CONVECTIVE POTENTIAL
DECENTLY SATURDAY NIGHT. FOR NOW WE WILL JUST CARRY CHC POPS, AS
IT IS NOT REAL CLEAR ON WHAT IMPACT ANY UPSTREAM CONVECTION MIGHT
HAVE ON OUR CWA. IT APPEARS THAT THE BULK OF THE ACTIVITY, IF IT
WERE TO OCCUR WOULD BE DIURNALLY DRIVEN AND NOT MUCH IN AREAL
COVERAGE.
AS FOR TEMPERATURES, WE WENT CLOSER TO THE LOWER ETA MOS FOR
FRIDAY'S HIGHS AS THE GFS MOS LOOKS TO WARM /WHICH HAS BEEN THE CASE
THIS SUMMER FOR MOST PLACES/. PLUS, THE DAYTIME HEATING WILL LIKELY BE
GOING INTO EVAPORATING MORE OF THE GROUND MOISTURE FROM YESTERDAY'S
DELUGE IN MANY AREAS. FOR SATURDAY, WE GENERALLY UTILIZED A BLENDED
APPROACH.
LONG TERM /SUNDAY THROUGH THURSDAY/
THE GENERAL LONG WAVE UPPER-LEVEL PATTERN WILL SUPPORT TROUGHING
OVER THE EASTERN UNITED STATES DURING THIS TIME FRAME. WHILE THE
OVERALL MODELS SUPPORT THIS IDEA, THERE ARE DIFFERENCES NOTED IN
THE TIMING OF THE DETAILS. OUR CONFIDENCE IS HIGH REGARDING THE
PATTERN EVOLUTION, HOWEVER IT IS LOWER WITH RESPECT TO THE
INDIVIDUAL DETAILS.
A SIGNIFICANT PLAYER IN THE PATTERN IS THE EVOLUTION OF THE
ENERGY THAT IS GENERALLY FORECAST TO TRAVEL FROM THE PACIFIC
NORTHWEST THROUGH THE MEAN RIDGE AND THEN AMPLIFY INTO THE EASTERN
NORTH AMERICA TROUGH. THE GFS ENSEMBLES INDICATE THE GFS
AMPLIFICATION OVER THE UPPER MIDWEST AND GREAT LAKES REGION AND
ASSOCIATED GREAT LAKES SURFACE LOW BY WEDNESDAY AND THURSDAY SEEMS
TOO FAR WESTWARD. THIS SOLUTION ALSO HAS LITTLE ENSEMBLE SUPPORT.
HPC MENTIONED THAT IN CONTRAST TO THE GFS SURFACE LOW, BY THURSDAY
THE RECENT ECMWF/CMC ENSEMBLE MEANS AND GFS ENSEMBLE MEANS ALL
SHOW HIGH PRESSURE OVER THE GREAT LAKES. THE ECMWF CONFORMS
SOMEWHAT BETTER TO THE CONSENSUS BUT COULD STILL BE A TAD STRONG
WITH ITS EVOLUTION. HPC GUIDANCE WENT WITH A BLEND OF THE 00Z
GFS/ECMWF SUNDAY WHICH SEEMS TO ACCOUNT FOR MOST MINOR DIFFERENCES.
FOR MONDAY THROUGH THURSDAY THOUGH, A PREFERENCE OF A NEARLY EVEN
BLEND OF THE 00Z GFS ENSEMBLE MEAN, THE 00Z ECMWF ENSEMBLE MEAN
AND THE 00Z ECMWF WAS UTILIZED. THIS SOLUTION EMPHASIZES THE
CONTINUED AGREEMENT UPON THE LARGE SCALE MEAN PATTERN AND FAVORED
FEATURE WITHIN, WHILE ALLOWING FOR THE MODEST CHANCE THAT THE
NORTHERN STREAM ENERGY IN SOME FORM, MAY SUPPORT AN ORGANIZED AND
PRECIPITATION FOCUSING WAVE ALONG THE PERSISTENT CENTRAL TO
EASTERN UNITED STATES FRONT DURING THE MID TO LATE PERIOD OF NEXT
WEEK. WE UTILIZED HPC GUIDANCE AS A STARTING POINT, THEN MADE SOME
MAINLY MINOR ADJUSTMENTS BASED ON LOCAL AFFECTS, COLLABORATION AND
SOME NEW 12Z MODEL GUIDANCE.
BASED ON THE ABOVE, A COLD FRONT WILL BE MOVING ACROSS THE AREA
SUNDAY. GIVEN THE UPPER-LEVEL TROUGHING AND ITS FORECAST POSITION,
THE LOW-LEVEL FRONTAL BOUNDARY MAY TEND TO STALL NEARBY SUNDAY NIGHT
AND LINGER FOR AWHILE EARLY IN THE WEEK. WITH A WEAK AREA OF HIGH
PRESSURE FORECAST TO BUILD ACROSS THE GREAT LAKES REGION WEDNESDAY
NIGHT AND THURSDAY, THE STALLED FRONTAL BOUNDARY MAY NOT GET PUSHED
TO FAR TO THE SOUTH. AS UPPER-LEVEL ENERGY MOVES WITH THE CYCLONIC
FLOW ALOFT FROM WEDNESDAY INTO THURSDAY, A WAVE OF LOW PRESSURE MAY
DEVELOP SOMEWHERE ALONG THE FRONT. THIS COULD ALLOW FOR AN
ENHANCEMENT OF THE SHOWER AND THUNDERSTORM THREAT. WE CONTINUE TO GO
WITH CHC POPS ON SUNDAY AS THE FRONT WILL BE IN OUR AREA, THEN TAPER
POPS DOWN BELOW SLIGHT CHC SUNDAY NIGHT INTO MONDAY. THE GFS MAY
HAVE SOME ERRONEOUS QPF BULLSEYES DUE TO CONVECTIVE FEEDBACK,
HOWEVER WITH THE FRONT ANTICIPATED TO BE SITTING JUST TO OUR EAST
AND SOUTH, WE BROUGHT SLIGHT CHC TO LOW CHC POPS ACROSS THE SOUTHERN
ZONES ON TUESDAY. IF THE CURRENT TIMING WORKS OUT, A WAVE OF LOW
PRESSURE POTENTIALLY TRAVERSING THE SURFACE FRONT MAY BRING A CHC OF
CONVECTION ON THURSDAY. FOR NOW WE WENT WITH LOW CHC POPS.
THAT IS ALL FOR NOW. THANKS TO THE SURROUNDING OFFICES/HPC FOR THE
COLLABORATION TODAY. HAVE A GOOD ONE!
AVIATION /19Z THURSDAY THROUGH TUESDAY/
FOR KABE AND KRDG AN UPPER AIR DISTURBANCE MOVING THROUGH
NORTHEASTERN PENNSYLVANIA HAS ALREADY DEVELOPED A FEW SHOWERS AND IT
IS UNSTABLE ENOUGH TO SUPPORT THUNDER. THE AREAL COVERAGE DOES NOT
SUPPORT THE MENTION OF THUNDERSTORMS AT EITHER TERMINAL. THE ENDING
OF THE PCPN WAS TIED TO THE FCST END OF THE DEEPER MOISTURE AND THE
FIRST LEAD SHORT WAVE OR UPPER AIR DISTURBANCE. A SECOND SHORT WAVE
OR UPPER AIR DISTURBANCE WILL MOVE THROUGH EARLY THIS EVENING AND
MIGHT CAUSE SOME CUMULUS TO LINGER. AFTER THAT SHORT WAVE MOVES THRU
SKIES SHOULD CLEAR. WE CARRIED SOME LIGHT MVFR FOG TOWARD MORNING
BECAUSE OF THE RECENT HEAVY RAIN. ON FRIDAY MORNING SOME OF THE
CIRRUS OVER THE MIDWEST WILL PASS OVERHEAD. CONVECTIVE TEMPS ARE
EXPECTED TO BE REACHED THUS A FEW TO SCATTERED DECK OF CUMULUS
CLOUDS SHOULD FORM AS THE MORNING PROGRESSES. ALL IN ALL A VFR DAY
AFTER ANY MORNING FOG BURNS AWAY.
FOR THE PHL METRO AREA AIRPORTS THEY WILL BE FARTHER REMOVED
FROM THE UPPER AIR DISTURBANCES AND WE HAVE NOT MENTIONED ANY
PRECIPITATION, JUST A BROKEN VFR CEILING. WE CARRIED CUMULONIMBUS IN
THE CLOUD GROUP AS SOME SHOULD FORM NW OF THE TERMINAL REGION BUT
CONFIDENCE IS NOT HIGH ENOUGH TO BELIEVE ACTUAL THUNDERSTORMS WILL
REACH THIS FAR SOUTHEAST. A SECOND SHORT WAVE OR UPPER AIR
DISTURBANCE WILL MOVE THROUGH EARLY THIS EVENING AND MIGHT CAUSE
SOME CUMULUS TO LINGER. AFTER THAT SHORT WAVE MOVES THRU SKIES
SHOULD CLEAR. WE CARRIED SOME LIGHT MVFR FOG TOWARD MORNING AT KPNE
AND KTTN BECAUSE OF THE RECENT HEAVY RAIN. WE BELIEVE THE MORE URBAN
NATURE AROUND KPHL AND A WEAK WEST WIND SHOULD PREVENT FOG FROM
FORMING THERE. ON FRIDAY MORNING SOME OF THE CIRRUS OVER THE MIDWEST
WILL PASS OVERHEAD. CONVECTIVE TEMPS ARE EXPECTED TO BE REACHED THUS
A FEW TO SCATTERED DECK OF CUMULUS CLOUDS SHOULD FORM AS THE MORNING
PROGRESSES. ALL IN ALL A VFR DAY AFTER ANY MORNING FOG BURNS AWAY.
FOR KMIV AND KACY THEY ARE EVEN FURTHER REMOVED FROM THE UPPER AIR
DISTURBANCES AND WE DID NOT MENTION ANY ADDITIONAL PRECIPITATION OR
CUMULONIMBI AT ALL. THE SECOND SHORT WAVE OR UPPER AIR DISTURBANCE
WILL MOVE THROUGH EARLY THIS EVENING TO THE NORTH AND MIGHT CAUSE
SOME CUMULUS TO LINGER. WE ENDED IT SOONER THAN PLACES FARTHER TO
THE NORTHWEST. WE CARRIED SOME LIGHT MVFR BECAUSE OF THE RECENT
HEAVY RAIN. ON FRIDAY MORNING SOME OF THE CIRRUS OVER THE MIDWEST
WILL PASS OVERHEAD. CONVECTIVE TEMPS ARE EXPECTED TO BE REACHED THUS
A FEW TO SCATTERED DECK OF CUMULUS CLOUDS SHOULD FORM AS THE MORNING
PROGRESSES. ALL IN ALL A VFR DAY AFTER ANY MORNING FOG BURNS AWAY.
OUTLOOK...
THE NEXT THREAT OF TSTMS IS SATURDAY AND SUNDAY AS MOISTURE
RETURNS FROM THE SW AND ANOTHER COLD FROM COMES THROUGH FROM THE
WEST. THERE SHOULD BE SOME MVFR AND IFR CONDITIONS DEVELOP DURING
THE CONVECTION WITH THE BETTER CHANCE OF IT OCCURRING SUNDAY. THEN
OVERALL VFR CONDITIONS EXPECTED MONDAY AND TUESDAY AS LONG AS THE
FRONT SAGS FAR ENOUGH TO OUR SOUTH. CONFIDENCE AT THIS POINT IS
HIGHEST NORTH OF PHL AND LOWEST FOR KMIV AND KACY.
MARINE
SCA WILL BE CONTINUED INTO THE NIGHT FOR OUR AREA WATERS AS THE
SOUTHERLY SWELLS SHOULD PERSIST INTO THE EVENING. AS THE FLOW BACKS
AND WEAKENS MORE TO THE WEST THE SWELLS SHOULD SUBSIDE AND WE SHOULD
REMAIN BLO SCA CRITERIA FOR SEAS INTO FRIDAY NIGHT. A SLIGHTLY
WEAKER VERSION OF THE PATTERN WE JUST HAD FOR TUESDAY AND WEDNESDAY
IS THEN EXPECTED TO RETURN FOR THE WEEKEND AS A SLOW MOVING COLD
FRONT IS FORECAST TO MOVE INTO AND THROUGH THE REGION BY MONDAY
MORNING. WHILE WINDS SHOULD REMAIN BLO SCA CRITERIA, A SOUTHERLY
SWELL MIGHT BRING US TO SCA CRITERIA PRIOR TO THE CFP. ATTM WE ARE
KEEPING SEAS JUST BELOW SCA CRITERIA, BUT WILL BEAR WATCHING OVER
THE NEXT COUPLE OF DAYS. THE GRADIENT SHOULD THEN WEAKEN AS THE
FRONT STALLS OVER OR JUST SOUTHEAST OF OUR AREA WATERS LATER MONDAY
INTO TUESDAY.
RIP CURRENTS...
A MODERATE RISK OF RIP CURRENTS HAS COME TO FRUITION AS THERE ARE
SOME BATHING RESTRICTIONS REPORTED ALONG THE OCEAN AND ATLANTIC
COUNTY BEACHES. AS THE WINDS BACK TO THE WEST, THE RIP CURRENT RISK
SHOULD DECREASE FOR TOMORROW. PLEASE FOLLOW THE DIRECTION OF BEACH
PATROL PERSONNEL IN YOUR AREA AND NEVER SWIM WHEN THERE ARE NO
LIFEGUARDS ON DUTY.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT FRIDAY FOR ANZ450>455.
SYNOPSIS...GORSE
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...GORSE/HPC
AVIATION...GIGI
MARINE...GIGI
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page