EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
114 PM EDT MON SEP 15 2008
 
VALID 12Z THU SEP 18 2008 - 12Z MON SEP 22 2008
 
PRELIMINARY UPDATE...

USED THE 00Z ECMWF FOR THE FRONTS AND PRESSURES FOR DAYS 3 THROUGH
5...WITH A FAIRLY EVEN BLEND WITH THE 00Z ECMWF ENSEMBLE MEAN
THEREAFTER TO REFLECT THE UNCERTAINTIES IN DETAIL INHERENT AT THAT
TIME RANGE.  THE MOST FUNDAMENTAL DIFFERENCE AMONG THE 00Z
NUMERICAL MODELS IS OVER THE NORTHEAST PACIFIC LATE IN THE
PERIOD...WHERE THE GFS...ECMWF...AND EC MEAN ALL SHOW CONSIDERABLE
SHORTWAVE ENERGY PUSHING INTO WESTERN CANADA AND THE NORTHWESTERN
UNITED STATES...WHILE THE GEFS MEAN INDICATES A SIZABLE RIDGE
ACROSS THE REGION.  THE GEFS MEAN DOES HAVE A HIGH DEGREE OF
SPREAD AMONG ITS INDIVIDUAL MEMBERS...HIGHER THAN THE EC MEAN...SO
THE IMPLICATION IS THAT THERE ARE ENSEMBLES CLOSER TO THE
DETERMINISTIC GFS.  BECAUSE OF THE LOWER LIKELIHOOD THAT THE GEFS
MEAN WILL GET THE PATTERN RIGHT...CHOSE THE EUROPEAN CENTRE
PRODUCTS FOR BETTER CONSISTENCY.  A LATE SEASON SUBTROPICAL RIDGE
SHOULD DOMINATE THE REMAINDER OF THE NATION....WITH ONLY THE
NORTHERN TIER OF STATES SEEING ANY INTRUSION OF COOL AIR.

FINAL...

THE 12Z GEFS MEAN IS A MARKED DEPARTURE FROM THE 00Z
VERSION...MATCHING WELL WITH THE BLEND USED TO CREATE THE
PRELIMINARY UPDATE PACKAGE ACROSS THE UNITED STATES.  THE RIDGE
ALONG THE BRITISH COLUMBIA COAST IS GONE...WITH SIGNIFICANT HEIGHT
FALLS INDICATED INTO THE PACIFIC NORTHWEST DAYS 6 AND 7.  THE 12Z
DETERMINISTIC GFS IS OUT OF SYNC WITH THIS MEAN...BOTH OVER THE
NORTHWEST LATE IN THE PERIOD AND ALONG THE SAINT LAWRENCE SEAWAY
AS EARLY AS DAY 4.  OVERALL...LOOKS LIKE A QUITE PERIOD FOR THE
NEXT WEEK.


CISCO