662
FXUS02 KWNH 031344
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
943 AM EDT THU JUL 03 2008
VALID 12Z MON JUL 07 2008 - 12Z THU JUL 10 2008
UPDATED MEDIUM RANGE PROGS SUBSTITUTED THE NEW 00Z/03 ECMWF
ENSEMBLE MEAN FOR THE EARLIER 12Z/02 MEAN THAT HAD BEEN USED IN
THE EARLIER PRELIM GRAPHICS.
THE PATTERN DURING THE MEDIUM RANGE PERIOD BEARS THE INDELIBLE
STAMP OF MIDSUMMER ACROSS NORTH AMERICA...WITH THE POLAR JET
RETREATED TO CANADA...AND THE FAR SOUTHERN UNITED STATES GRADUALLY
BECOMING SUBJECT TO DISTURBANCES IN THE EASTERLIES. ONE SUCH
INVERTED TROF DEVELOPS AS HEIGHT RISES OCCUR N OF A SHEAR AXIS
OVER THE LOWER MS VLY MON DAY 4...POSSIBLY LEAVING BEHIND A WWD
DRIFTING UPPER TROF/LOW OVER SRN TX AROUND TUE DAY 5. THERE IS A
FAIR AMOUNT OF MODEL SPREAD CONCERNING THIS INVERTED UPPER TROF
FEATURE...SO WE ARE LESS THAN CONFIDENT WITH ITS PRECISE DETAILS.
ALSO...THE 00Z GEFS MEAN IS SUSPECT WITH THE DEPTH OF THE TROUGH
IT DEPICTS ALONG THE WESTERN CANADIAN BORDER LATE IN THE PERIOD.
IT IS DEEPER THAN EITHER THE 00Z/03 DETERMINISTIC ECMWF OR 00Z/03
GFS...SO WE LEAN AWAY FROM THE 00Z GEFS SOLUTION. THAT LEAVES THE
12Z/00Z/03 ECMWF AND ITS ENSEMBLE MEANS...WHICH HAD EXCELLENT RUN
TO RUN CONTINUITY... TO CONSTRUCT THE UPDATED PRELIMINARY FRONTS
AND PRESSURES FOR DAYS 3 THROUGH 7. THE INCORPORATION OF THE ECMWF
MEAN WILL DE-EMPHASIZE THE QUESTIONABLE MID LEVEL UPPER LOW VCNTY
OF GA DURING THE SECOND HALF OF THE FORECAST.
AT THIS TIME HPC PREFERS TO STAY ON THE MORE CLIMATOLOGICAL ECMWF
ENSEMBLE SIDE OF THE ENVELOPE OF SOLUTIONS...WHICH BECOME OUT OF
PHASE WITH GEFS FEATURES IN THE NRN BRANCH OF WESTERLIES
ESPECIALLY DAYS 5-7.
CISCO/FLOOD
A
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