862
FXUS02 KWBC 281825
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
224 PM EDT TUE JUL 28 2009
VALID 12Z FRI JUL 31 2009 - 12Z TUE AUG 04 2009
PRELIMINARY UPDATE...
THE PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7 WERE
UPDATED USING THE 00Z/28 ECMWF THROUGH DAY 5...WITH A SMALL
INCORPORATION OF THE 00Z/28 EC ENSEMBLE MEAN THEREAFTER TO
MITIGATE UNCERTAINTIES IN SYNOPTIC DETAIL INHERENT TO THAT TIME
RANGE. THE 00Z/28 GFS WAS UNUSUALLY IN SYNC WITH THE
DETERMINISTIC ECMWF WITH THE MAJOR SHORTWAVE CROSSING THE GREAT
LAKES DAY 6...ADDING A GREAT DEAL OF CONFIDENCE TO THE FORECAST
THERE. THE ENTIRE PATTERN IS QUITE UNUSUAL FOR THE DOG DAYS OF
SUMMER...WITH AN ENORMOUS...AUTUMNAL STRENGTH HIGH NOSING INTO THE
NORTH CENTRAL STATES BY THE END OF THE PERIOD. THE BIG VORTEX OFF
THE WEST COAST LOOKS LIKE IT WILL STAY WELL OFFSHORE...ALLOWING
MUCH OF THE INTERIOR WEST TO CONTINUE TO BAKE...SIZZLE AND FRY.
FINAL UPDATE...
THE 12Z/28 GFS IS BUCKING CLIMATOLOGICAL RECORDS GOING BACK AT
LEAST 50 YEARS BRINGING THE VORTEX OFF THE WEST COAST INTO
CALIFORNIA THIS PARTICULAR PERIOD...ESSENTIALLY THE ANNUAL THERMAL
MAXIMUM FOR THE UNITED STATES...SO DISCOUNTED IT SUMMARILY THERE.
DOWNSTREAM...THE GFS MADE PROFOUND CHANGES FROM ITS 00Z/28 RUN
WITH THE PACING OF THE WAVES COMING THROUGH THE MAIN BAND OF
WESTERLIES DIPPING DOWN FROM CANADA...A POOR MARK FOR CONTINUITY.
THERE IS STILL SOME WIGGLE ROOM FOR THE EXACT EVOLUTION OF THE
SYSTEMS AFFECTING THE GREAT LAKES REGION DAYS 5 AND 6...BASED ON
THE LATEST GEM GLOBAL AND UKMET...BUT THE BLEND USED FOR THE
UPDATE PACKAGE IS AS SOLID AS ANY...SO SAW NO COMPELLING REASON TO
MAKE CHANGES ACROSS THE NATION FOR THE FINAL ISSUANCE.
CISCO
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