872
FXUS02 KWBC 081818
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
217 PM EDT FRI AUG 08 2008
VALID 12Z MON AUG 11 2008 - 12Z FRI AUG 15 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. DETAIL DIFFERENCES WITH
THE POLAR VORTEX IN NORTHERN CANADA...LARGE DAY TO DAY DIFFERENCES
IN THE GUIDANCE...AND TWO DISTINCTLY DIFFERENT EVOLUTIONS FOR A
DEEP CYCLONE MOVING ACROSS WESTERN CANADA EARLY IN THE PERIOD LEAD
TO GREATER THAN NORMAL UNCERTAINTY. IN THE EAST...SHORT RANGE
MODEL TRENDS LED TO A SIGNIFICANTLY FARTHER SOUTH CYCLONE/COLD
FRONT SOLUTION THAN CONTINUITY ADVERTISED. MOST OF THE GUIDANCE
DEFLECTS THE CANADIAN SYSTEM NORTHWARD AROUND THE WEST SIDE OF
RIDGING IN CENTRAL CANADA. WHILE ENERGY MAY UNDERCUT THIS RIDGE
NEAR THE CENTRAL US/CANADIAN BORDER...THE 00Z GFS IS TOO FAR TO
THE SOUTHWEST WITH ITS ALTERNATIVE TRACK AND WAS NOT USED. ONE
WAY OR ANOTHER...THE MODEL GUIDANCE CONVERGES UPON A NEARLY CLOSED
VORTEX NEAR THE EASTERN US/CANADIAN BORDER WHICH KEEP STANDARDIZED
ANOMALIES OF THE 500 HPA HEIGHT FIELD 2-3 STANDARD DEVIATIONS
BELOW NORMAL...CHOSE A ECMWF DOMINANT SOLUTION WITH A SLIGHT
BLENDING IN OF THE ECMWF MEAN DAYS 6 AND 7.
BOUNDARY AT THE SRN EDGE OF THE WESTERLIES FROM THE LOWER RED
RIVER VALLEY SEWD ACROSS THE GULF COAST WILL PROVIDE A FOCUS FOR
CONVECTION THIS PERIOD. ADDITIONAL MDT TO LOCALLY HVY RAIN
POTENTIAL OVER NEW ENG NEAR A POSSIBLE CLOSED MID LEVEL LOW
THURS-SAT.
12Z GFS TRENDING TOWARDS CMC AND ECMWF AS IT SLOWS THE SW
ADVANCEMENT OF THE SRN CANADIAN PLAINS MID LEVEL CLOSED LOW..STILL
FASTER THAN THE OTHER MODELS BUT DISTINCTLY SLOWER THAN PRIOR GFS
RUNS. NO CHNAGES TO MORNING PRELIMS.
ROTH/ROSENSTEIN
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