PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
753 AM EDT TUE MAY 05 2009
 
VALID 12Z SAT MAY 09 2009 - 12Z TUE MAY 12 2009
 
THE LATEST DETERMINISTIC AND ENSEMBLE SOLUTIONS MAINTAIN
REASONABLE CONTINUITY THROUGH THE MEDIUM RANGE PERIOD. A DEEP
VORTEX OVER THE CANADIAN ARCHIPELAGO HELPS MAINTAIN A LOW
AMPLITUDE TROUGH OVER THE NORTHEAST FOR MOST OF THE PERIOD...WHILE
THE FLOW ACROSS THE PACIFIC UNDER THE BASE OF A POSITIVE ANOMALY
NEAR FAR EASTERN ASIA RESULTS IN A CUTOFF LOW IN THE NORTHEAST
PACIFIC THAT EVENTUALLY EJECTS TOWARD THE PACIFIC NORTHWEST OR
SOUTHWEST CANADA LATE IN THE PERIOD. THROUGH THE MID-LATITUDES...A
QUASI-ZONAL SOUTHERN STREAM CONTINUES TO MOVE THROUGH THE LOWER
48.  

INTERESTINGLY...TELECONNECTIONS MOST FAVOR THE 00Z GEFS AND 00Z
ECMWF ENSEMBLE MEANS...SHOWING A SLOWER PROGRESSION WITH THE
SYSTEM APPROACHING THE WESTERN US/CANADIAN BORDER EARLY NEXT WEEK.
 MODEL DIFFERENCES ARE LESS SIGNIFICANT THAN SEEN THIS TIME
YESTERDAY...AS THE ECMWF HAS SIGNIFICANTLY BACKED OFF ITS DEEP
CYCLONE MOVING THROUGH THE WEST.  HOWEVER...THE 06Z GFS LOOKS
SIMILAR TO YESTERDAYS ECMWF SOLUTIONS.  EARLY ON...A 50/50 BLEND
OF THE 00Z OR 06Z GFS/00Z ECMWF WAS A REASONABLE STARTING POINT
FOR CREATING THE PRESSURES/FRONTS INTO SATURDAY.  THEREAFTER...A
BLEND OF THE 00Z ECMWF AND ITS ENSEMBLE MEAN /WHICH IS CLOSE TO
THE 00Z GEFS MEAN/ ACCOUNTS FOR THE PROGRESSION DIFFERENCE WITH
THE SYSTEM MOVING FROM THE NORTHEAST PACIFIC INTO WEST-CENTRAL
NORTH AMERICA WHICH ALSO KEEPS MORE IN LINE WITH THE
TELECONNECTION-FAVORED PATTERN OF TROUGHING LINGERING OFFSHORE
WESTERN CANADA.

ROTH/JAMES