768
FXUS02 KWBC 261808
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
208 PM EDT WED AUG 26 2009
VALID 12Z SAT AUG 29 2009 - 12Z WED SEP 02 2009
MODELS AND THEIR ENSEMBLES SHOW NEAR AVERAGE AGREEMENT THIS CYCLE
CONCERNING THE LONGWAVE FLOW IN THE MEDIUM RANGE PERIOD...WITH A
DEEP UPPER TROUGH OVER THE NORTHEAST PACIFIC MOVING STEADILY INTO
WESTERN NORTH AMERICA...WHICH SLOWLY LIFTS AN UPPER LOW OUT OF THE
GREAT LAKES TOWARD THE END OF THE PERIOD. THE MAIN ISSUES TODAY
INVOLVE THE AMPLITUDE AND SPEED OF INDIVIDUAL SHORTWAVE
TROUGHS...WITH THE DIFFERENCES BECOMING INCREASINGLY DRAMATIC
AFTER DAY 5. THE GFS IS NEAR THE FAST EDGE OF THE GUIDANCE WITH
ITS MID/UPPER LEVEL FLOW ACROSS THE NORTHERN CANADIAN
PROVINCES...WHICH THEN LIFTS THE UPPER LOW OUT OF THE GREAT LAKES
FASTER THAN MOST OTHER SOLUTIONS. MEANWHILE...THE ECMWF IS ABOUT A
DAY FASTER THAN THE GFS WITH A PORTION OF THE NORTHEAST PACIFIC
TROUGH SEPARATING INTO A CLOSED LOW NEAR THE PACIFIC NORTHWEST BY
DAY 7. TO ADDRESS THESE AND OTHER MODEL DIFFERENCES...EARLY
PRELIMS USED AN 80/20 OPERATIONAL ECMWF/ECMWF ENSEMBLE MEAN BLEND
DAYS 3/4...THEN TRANSITIONING TO A 40/60 OPERATIONAL ECMWF/ECMWF
ENSEMBLE MEAN BLEND BY DAY 7. THIS APPROACH DISCOUNTS THE FASTER
GFS SOLUTION IN THE EAST WHILE AVERAGING THE TIMING DIFFERENCES IN
THE WEST.
UPDATED MORNING PRELIMS...THESE ARE CHANGED TO A BLEND OF OP CMC
AND OP ECMWF OVER CONUS WITH AN ATTEMPT TO RESOLVE THE LARGE
DIFFERENCES WITH THE EAST COAST TROPICAL SYSTEM DAY 3
SAT. A 50/50 BLEND OF ECMWF AND CMC USED WITH A SLIGHT MANUAL
ADJUSTEMENT SOUTHEAST FOR THE MID ATLANTIC LOW. DAYS 6-7 BLEND GFS
ENS MEAN AND ECMWF ENS MEAN. CMC WHILE ACCEPTABLE OVER THE EAST
LEAVES OFFSHORE AN ELONGATED TROF OFF THE B.C. COAST WHILE GFS AND
ECMWF BRING IT DOWN STRONGER WITH ECMWF THE FASTEST. BY DAY 7 BOTH
00Z/06Z RUNS OF GFS AND ECMWF HAVE A LARGE CLOSED LOW OFF THE PAC
NW/NRN CA COAST. PREFER AT THIS TIME TO USE A BLEND OF BOTH
GFS/ECMWF ENS MEAN HERE WHICH KEEPS A SIG TROF BUT NOT YET A
CLOSED LOW.
12Z MODEL GUIDANCE OF GFS DIFFERS WITH THE LATE PERIOD GLFAK TROF
BY DROPPING SEWD CLOSED LOW. ENOUGH DIFFERENCES HERE TO CONT TO
USE THE 00Z GFS/ECMWF ENS MEAN.
AFTN FINALS HAVE LITTLE CHANGE FROM UPDATED PRELIMS
EAST COAST/TROPICS...
T.S.DANNY CONTS TO INTENSIFY. GLOBAL MODELS CONT TO HAVE A MORE
WESTERLY TRACK WHILE IT INTERACTS WITH A LINGERING MID LEVEL TROF
OVER ERN CONUS LATE THURSDAY AND EARLY FRIDAY ALLOWING IT TO LIFT
RAPIDLY NWD WHILE HURRICANE MODEL GUIDANCE CONTS TO CLUSTER WITH A
MORE OFSHORE TRACK. ALL PHASE DIAGRAM GUIDANCE INDICATES A
MDT/DEEP SYMETRIC WARM CORE LOW BECOMING BAROCLINIC ONCE IT
REACHES HIGHER LATITUDES. DAYS 3-5 SAT/MON POSITIONS REFLECT THE
NHC FORECASTS. THIS SYSTEM WILL AFFECT THE MID ATLC AND NEW ENG
COAST FRI-SUN WITH HEAVY RAINS AND HIGH WINDS. SRN NEW ENG MOST
AFFECTED WITH THIS SYSTEM WITH A LARGE AREA OF 3 INCH PLUS
RAINFALL. SEE NHC/TPC ADVISORIES/WARNINGS.
JAMES/ROSENSTEIN
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