048
FXUS02 KWBC 011755
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
155 PM EDT SAT AUG 01 2009
VALID 12Z TUE AUG 04 2009 - 12Z SAT AUG 08 2009
WITH BETTER AGREEMENT BETWEEN THE DETERMINISTIC ECMWF AND THE MOST
RECENT EC ENSEMBLE MEAN...USED A PROGRESSIVE BLEND OF THIS
GUIDANCE FOR THE PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3
THROUGH 7. THE DETERMINISTIC ECWMF FROM 00Z/31 PULLED THE VORTEX
OVER THE EASTERN PACIFIC WELL OFFSHORE...WHICH DID NOT LINE UP
WITH THE PREVIOUS MEANS OR THE DETERMINISTIC GFS FROM THAT RUN.
NOW THE OPERATIONAL GUIDANCE...INCLUDING THE CURRENT GEM
GLOBAL...SHOW THIS VORTEX EVENTUALLY EJECTING ACROSS THE NORTHERN
INTERMOUNTAIN REGION...SO WENT WITH THIS SCENARIO. THE 00Z/01 GFS
IS SUFFICIENTLY OUT OF SYNC WITH THE MORE ROBUST AND BETTER
PERFORMING EUROPEAN CENTRE GUIDANCE TO RENDER ITS SOLUTION OF
LITTLE USE THIS FORECAST...PARTICULARLY WITH ITS HANDLING OF THE
WAVE CROSSING THE MID ATLANTIC REGION LATE DAY 5.
UPDATED MORNING PRELIMS AGAIN TODAY MAKE USE THE 00Z ECMWF ENS
MEAN AND LAGGED AVERAGE FORECASTS OF GFS/ECMWF AND A COMBINATION
OF BOTH. COMBINED LAGGED AVERAGE FORECAST AGAIN VERY SIMILAR TO A
00Z ECMWF ENS MEAN. PROBLEM REMAINS THE SAME...HOW MUCH
PROGRESSION DOES THE DEEP OFFSHORE CA COASTAL CUTOFF LOW HAVE
DURING THIS PERIOD. LATEST 06Z GFS STAYS THE COURSE WITH THE 00Z
GFS RUN KEEPING IT OFFSHORE OF THE PAC NW COAST AND ALLOWING A
MUCH DEEPER ERN TROF TO REMAIN AND RELOAD WHILE
ECMWF/CMC/UKMET/NOGAPS ARE PROGRESSIVE AND BRING THE LOW INLAND AS
AN AMPLIFIED TROF AND RAISE DOWNSTREAM HTS OVER CENTRAL AND ERN
CONUS AFTER DAY 5 THURSDAY.
HPC MORNING PREFERNCE IS TOWARDS THE ECMWF/UKMET/CMC/LAGGED
AVERAGE COMBINATION OF GFS/ECMWF AND ECMWF ENS MEAN LATE PERIOD
WHICH BRINGS A TROF INLAND WITH ITS AXIS ALONG 120W AND RAISES HTS
CONSIDERABLY FROM THE MS VALLEY EWD.
12Z GFS BEGINS SHOWING MORE EPAC COASTAL PROGRESSION AFTER DAY 5
THUS AND IS LEANING MUCH MORE STRONGLY TOWARDS THE 00Z AND NEW 12Z
GFS ENS MEAN WITH WRN SHORTWAVE PROGRESSION AND RAISING ERN CONUS
HTS LATE PERIOD. 12Z CMC FOLLOWS CONTINUITY.
NO CHANGES MADE IN AFTN FINALS FROM EARLY MORNING PRELIM UPDATES.
CISCO/ROSENSTEIN
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