298
FXUS02 KWBC 151929
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
329 PM EDT TUE SEP 15 2009
VALID 12Z FRI SEP 18 2009 - 12Z TUE SEP 22 2009
PRELIMINARY UPDATE...
THE PRELIMINARY FRONTS AND PRESSURES FOR DAYS 3 THROUGH 7 WERE
UPDATED WITH A PROGRESSIVE BLEND FROM THE 00Z/15 ECMWF TOWARD THE
00Z/15 EC ENSEMBLE MEAN. THE 00Z/15 GFS IS ALONE IN ITS PHASING
OF POLAR AND ARCTIC STREAMS OVER THE UPPER MIDWEST DAY 7...WITH
THE OTHER GUIDANCE KEEPING THE ARCTIC AIR WELL TO THE NORTH OVER
CENTRAL CANADA. THE 00Z/15 GEM GLOBAL IS OUT OF SYNC SEEMINGLY
EVERYWHERE...FROM THE DEEP LOW PASSING SOUTH OF NOVA SCOTIA EARLY
IN THE PERIOD...TO THE BROAD SURFACE RIDGE WEST OF BRITISH
COLUMBIA AT THE END OF THE FORECAST. THE LAST THREE EC ENSEMBLE
MEANS HAVE SETTLED INTO A MORE STABLE SOLUTION...WITH THE LATEST
DETERMINISTIC ECMWF WELL WITHIN THEIR BOUNDARIES.
FINAL...
AS WITH YESTERDAYS ARRIVAL OF THE 12Z GUIDANCE...THERE IS LITTLE
TO HANG THE HAT ON FOR THE PROBLEMS MOST PLAGUING THE MEDIUM
RANGE. THE NEW ECMWF HAS SPED UP THE LOW DEVELOPING EAST OF NEW
ENGLAND DAYS 4 AND 5 FROM ITS 00Z/15 VERSION. PREFERRED TO STICK
WITH THE BLEND USED FOR THE PRELIMINARY UPDATE HERE...CONSIDERING
THE APPRECIABLE ENSEMBLE SUPPORT THAT SOLUTION HAD. THE NEXT
CONTENTIOUS ISSUE IS THE AMPLITUDE AND DEGREE OF PHASING WITH THE
MAJOR TROUGH DIGGING INTO THE NORTH CENTRAL STATES LATE IN THE
PERIOD. THE GFS CONTINUES TO BE MORE PHASED THAN THE OTHER
GUIDANCE...OWING TO A RIDGE BUILDING STRONGLY UP THE BRITISH
COLUMBIA COAST. THE GEM GLOBAL IS THE FLATTEST OF THE
MODELS...WITH A PACIFIC JET IRONING THE FLOW STICK STRAIGHT ALONG
THE CANADIAN BORDER. THE UKMET CLUSTERS QUITE WELL WITH THE LAST
TWO RUNS OF THE ECMWF OVER THIS REGION...ADDING CONFIDENCE TO THE
SOLUTION ADOPTED FOR THE UPDATE PACKAGE.
CISCO
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