PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
858 AM EST TUE DEC 11 2012

VALID 12Z SAT DEC 15 2012 - 12Z TUE DEC 18 2012

THE 11-00Z ECMWF/GFS ENSEMBLE AND OPERATIONAL PACKAGES WERE IN
DECENT AGREEMENT...ESPECIALLY THROUGH DAY 5 AND ACROSS MUCH OF THE
NORTH PACIFIC OCEAN. THIS BODE WELL WITH CONTINUITY AND THE
MIDSHIFT PRELIMINARY FRONTS. SO MINIMAL CHANGES WERE REQUIRED. AND
EVEN THEN...AT THE END OF DAY 5....THERE WAS NOT MUCH MORE TO ADD
THAN AN EXTRA CLOSED ISOBAR IN THE PACIFIC NORTHWEST AND MIDWEST. 

A BLEND OF THE 11-00Z ECMWF/GEFS MEANS ALOFT DROVE THE DAY 6-7
FORECAST AND ALLOWED FOR A PROGRESSIVE FLOW AND WAVE TRAIN TO BE
IDENTIFIED...MOVING ABOUT 10 DEGREES OF LONGITUDE IN A 24 HOUR
PERIOD.  THE PRIMARY H5 TROUGH AXES ON DAY 7 BEING ALONG
90-95W...120-125W AND 155-160W IN THE GULF OF ALASKA. SMALLER
SCALE DETAILS EMBEDDED WITHIN THE PROGRESSIVE LONGWAVE PATTERN
BETWEEN 40-50N LAT...ESPECIALLY DOWNWIND OF THE CONTINENTAL DIVIDE
WERE FAR FROM PERFECT AMONG THE 00Z GUIDANCE PACKAGES AVAILABLE.
HOPEFULLY...THE 12Z CYCLE WILL BEGIN TO DRAW SOME CONCLUSIONS
ABOUT THE STORM TRACK EMBEDDED WITHIN THE 'MEAN H5 FLOW' PATTERN
EAST OF THE ROCKIES.
VOJTESAK