321
FXUS02 KWBC 091808
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
208 PM EDT SAT AUG 09 2008
VALID 12Z TUE AUG 12 2008 - 12Z SAT AUG 16 2008
MODELS AGREE ON THE GENERAL FLOW PATTERN WITH TROUGHING IN THE
EAST WITH A MID LEVEL WEAKNESS NEAR THE PACIFIC COAST OF THE
CONTINENT AND RIDGING ACROSS THE ROCKIES. LARGE DAY TO DAY
DIFFERENCES CONTINUE TO BEEN SEEN AMONGST MOST OF THE
GUIDANCE...EXCEPT THE 00Z GFS NEAR THE US/CANADIAN BORDER WHICH
HAS BEEN REMARKABLY CONSISTENT. MODEL GUIDANCE CONTINUES TO
INDICATE A NEARLY CLOSED VORTEX ACROSS THE NORTHEAST THIRD OF THE
COUNTRY LATE IN THE PERIOD WHICH MOVES EAST-SOUTHEAST FROM
SOUTHERN CANADA ACROSS THE UPPER MISSISSIPPI VALLEY. THIS
REINFORCEMENT OF THE EASTERN TROUGH WOULD MAINTAIN STANDARDIZED
ANOMALIES OF THE 500 HPA HEIGHT FIELD 2-3.5 STANDARD DEVIATIONS
BELOW NORMAL...KEEPING TEMPERATURES ACROSS THE EAST..INCLUDING THE
NORTHEAST/MID ATLC AND SOUTHEAST REGIONS.. QUITE MILD FOR AUGUST.
WHILE THE GFS AND ECMWF RESEMBLE THE ECMWF AND NCEP/GEFS ENSEMBLE
MEANS...DETAIL DIFFERENCES REMAIN.
SFC PROGS BASED ON GFS/CMC/ECMWF AND THEIR MEANS THRU DAY 5 ARE
FAIRLY REASONABLE BUT HAVE ENOUGH DIFFERENCES FOR HPC TO USE A
DOMINENT BLEND OF ECMWF/GFS ENS MEANS AND TOTALLY GFS/ECMWF MEANS
FOR DAYS 6 AND 7.
12Z GFS DROPPING SWD ITS SRN CANADIAN/NRN PLAINS CLOSED LOW
TRENDING TOWARDS ECMWF SOMEWHAT BUT NOT NEARLY AS AGRESSIVE A
SOLUTION DAYS 6 AND 7. GFS ENS MEAN FROM 12Z STILL LIKE PRIOR
ECMWF AND GFS MENAS FROM THEIR 00Z RUNS OF AN ERN PAC TROF/ROCKIES
RIDGING ABND A MEAN TROF FROM THE GREAT LAKES TO ERN TX BY DAY 7
SAT. HPC FINALS WILL HAVE NO CHANGES FROM EARLIER PRELIMS BASED ON
CONTINUED OP MODEL DIFFERENCES BUT CONSISTENCY BETWEEN ENS MEAN
SOLUTIONS
ADD SOME CONFIDENCE.
ROTH/ROSENSTEIN
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