163
FXUS02 KWBC 121753
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
152 PM EDT WED AUG 12 2009
VALID 12Z SAT AUG 15 2009 - 12Z WED AUG 19 2009
THE GUIDANCE IS IN REASONABLY GOOD AGREEMENT CONCERNING THE
EVOLUTION OF THE LARGE SCALE PATTERN THIS PERIOD...WITH SYSTEMS
PROGRESSING THROUGH THE MID-LATITUDES AND CONTINUOUSLY EVOLVING
AND MOVING POSITIVE/NEGATIVE ANOMALY CENTERS ACROSS WESTERN
LONGITUDES. CHOSE TO START FRO OVERNIGHT PRELIMS WITH A 00Z
ECMWF/00Z CANADIAN COMPROMISE SOLUTION...WHICH LIE IN BETWEEN THE
00Z GEFS MEAN AND 12Z ECMWF ENSEMBLE MEAN SOLUTIONS...AND MADE
SOME ADJUSTMENTS TOWARDS THE 12Z MULTI-MODEL ENSEMBLE LOW PRESSURE
CENTER CLUSTERING.
UPDATED MORNING PRELIMS PREFER TO TREND TOWARDS ENS MEAN CONSENSUS
AND TO DAMPEN OUT INDIVIDUAL UNCERTAIN MODEL DETAILS. THUS HAVE
BLENDED OP GFS AND ECMWF AND TO LARGER DEGREE INCORPORATE A WELL
AGREED UPON GFS AND ECMWF ENS MEAN SOLUTION. THIS IN ESSENCE TAKE
THE DAY 3 SAT WRN CONUS TROF SLOWLY EWD WITH A POTENTIAL RELOADING
SHORTWAVE DROPPING SEWD THRU S CENTRAL CANADA WITH THE MEAN
PATTERN SETTING UP WITH A TROF ALONG 95W BY LATE PERIOD AND A WELL
AGREED UPON LONGER TERM TROF AXIS ALONG 90W WITH UPSTREAM RIDGING
CONTINUING OVER WRN CONUS.
06Z AND 12Z GFS RUNS DEVELOP A FASTER AND SHARPER TROF IN THE
PLAINS DAYS 6-7 IN RESPONSE TO BUILDING MORE UPSTREAM RIDGING OVER
THE PAC NORTHWEST AND B.C. GFS ENS MEANS REFLECT A MORE MODERATE
TROF MUCH LIKE THE 00Z GFS AND ECMWF ENS MEANS. CMC HAS DE
AMPLIFIED ITS FORECAST PATTERN DAYS 5-6 WITH LESS EPAC RIDGING AND
LESS DOWNSTREAM DIGGING CENTRAL CANADIAN AND CONUS TROF. UKMET HAS
A DEEP VORTEX BY DAY 6 OVER HUDSON BAY WITH A BROAD TROF COVERING
THE NRN AND CENTRAL PLAINS. BEST TO KEEP A BETTER AGREED UPON 00Z
GFS ENS AND ECMWF MEAN FOR LATE PERIOD AT THIS TIME. NO CHANGES TO
AFTN FINALS FROM UP DATED MORNING PRELIMS.
ATLANTIC TROPICS QUITE ACTIVE THIS PERIOD WITH T.D. TWO FORECAST
TO BECOME T.S. ANA. BY DAY SEVEN THIS SYSTEM MAY BE SOUTHEAST OF
THE SOUTH ATLANTIC SEABOARD WITH MOST GLOBAL MODELS SUPRESSING
INTENSITY AT THIS TIME BEYOND DAY 5. SECOND AFRICAN COASTAL WAVE
HAS AGITATED NEARLY ALL GLOBAL FORECAST MODELS WITH GFS LEADING
THE PACK IN ITS CYCLOGENESIS AND FORECAST SPEED. A WELL AGREED
UPON TRACK TOWARDS THE LESS ANTILLES AT T.S. STRENGTH OR GREATER
AS INDICATED BY A MODEL CONSENSUS BY DAY 7 WED. SEE NHC
DISCUSSIONS/ADVISORIES FOR THIS SYSTEMS. HPC PROGS REFLECT TPC AND
HPC COORDINATED POSITIONS.
ROTH/ROSENSTEIN
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