891
FXUS02 KWBC 181913
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
313 PM EDT TUE AUG 18 2009
VALID 12Z FRI AUG 21 2009 - 12Z TUE AUG 25 2009
PRELIMINARY UPDATE...
THE PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7 WERE
UPDATED PRIMARILY USING THE 00Z/18 ECMWF. THE LAST FOUR EC
ENSEMBLE MEANS HAVE TRENDED TOWARD MORE AMPLITUDE WITH THE TROUGH
CROSSING THE GREAT LAKES DURING THE FIRST HALF OF THE PERIOD...AND
TOWARD A SLOWER...SHARPER TROUGH APPROACHING BRITISH COLUMBIA BY
THE END OF THE FORECAST. THE LATEST DETERMINISTIC ECMWF REFLECTS
THESE TRENDS WELL...ADDING MORE RIGOR TO ITS SOLUTION. THE 00Z/18
GFS IS OUT OF SYNC WITH BOTH THE EUROPEAN CENTRE GUIDANCE AND THE
GEM GLOBAL MODEL DURING THE SECOND HALF OF THE PERIOD...SHOWING A
SPRAWLING POLAR VORTEX FROM HUDSON BAY EASTWARD. THE GEM GLOBAL
HANGS ONTO THE TROUGH OVER THE EASTERN UNITED STATES LONGER THAN
THE OTHER MODELS...AND WHILE THIS SOLUTION IS NOT OUT OF THE
QUESTION BASED ON THE SPREAD EVEN IN THE EC ENSEMBLE MEMBERS...THE
ODDS ARE AGAINST IT.
FINAL...
THE 12Z/18 GFS IS STILL OFFERING A SIGNIFICANTLY DIFFERENT
CONFIGURATION TO THE FLOW OVER EASTERN CANADA DURING THE SECOND
HALF OF THE FORECAST PERIOD THAN THE EUROPEAN CENTRE
GUIDANCE...DEPICTING A CONSOLIDATED VORTEX. THE 12Z/18 ECMWF IS
CLOSE TO ITS 00Z/18 SOLUTION...AND WHERE IT DOES DIFFER...IT IS
WITHIN TOLERANCE WITH THE MOST RECENT EC ENSEMBLE MEAN.
CISCO
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