196
FXUS02 KWNH 251400
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
859 AM EST WED NOV 25 2009
VALID 12Z SUN NOV 29 2009 - 12Z WED DEC 02 2009
THE UPDATED PRELIM GRAPHICS KEPT THE SAME GENERAL IDEAS OF THE
EARLY PRELIM BUT SUBSTITUTED THE NEW 00Z/25 ECENS MEAN FOR THE
OLDER CORRESPONDING 12Z/24 MEAN. OUR BLEND WAS 70% DETERMINISTIC
ECMWF EARLY IN THE PERIOD BUT TAPERED OFF TO 70% ECMWF ENSEMBLE
MEAN TOWARDS THE END OF THE PERIOD.
DESPITE BIG CONTINUITY CHANGES IN ITS LAST TWO RUNS FOR THE MIDDLE
OF NEXT WEEK...THE EUROPEAN CENTRE GUIDANCE STILL LOOKS MORE
STABLE THAN THE OTHER GLOBAL NUMERICAL MODELS...INCLUDING THE GFS
AND GEM GLOBAL...WITH THE HANDLING OF THE UPCOMING PATTERN. THE
MAIN FORECAST PROBLEM....FOR TUE-WED DAYS 6-7...APPEARS TO BE THE
POSSIBLE SPLITTING OF A TROF CROSSING THE MS RIVER INTO NRN AND
SRN STREAM PIECES OF ENERGY. THIS SPLITTING IS COMPLICATED BY A
THIRD SHOT OF ENERGY DROPPING INTO THE NRN ROCKIES AT THAT TIME
WITH ITS OWN POTENTIAL FOR SPLITTING INTO TWO PARTS. IT WAS
SOMEWHAT ENCOURAGING TO SEE THE NEW 00Z GFS PARALLEL RUN
SUPPORTING THE 00Z ECMWF WITH A POSITIVE TILT SPLITTING TROF
SCENARIO TUE DAY 6 VERSUS THE REGULAR GFS DEEP ONE PIECE SYS OVER
THE ERN CONUS. HOWEVER THE 06Z/25 PARALLEL RUN EVOLVED A WHOLE
DIFFERENT SCENARIO BY DAY 6 CREATING TWO CUTOFF LOWS FROM THE
SPLIT OFF SRN END OF THE NRN ROCKIES TROF AS WELL AS THAT OF THE
ERN CONUS TROF. THAT WILD 06Z GFS PARALLEL SOLUTION HAD NO SUPPORT
FROM THE 00Z/25 ENSEMBLE SPAGHETTI PLOTS...WHILE THE SPLITTING
SOLUTION OF THE 00Z DETERMINISTIC ECMWF HAS GOOD SUPPORT FROM
ECMWF/CANADIAN ENSEMBLE MEMBERS AND EVEN A FEW GFS ENSEMBLE
MEMBERS. BEHIND THAT SYSTEM...ALL THE MODELS SHOW AN INVASION OF
AT LEAST MODIFIED ARCTIC AIR OVER THE NORTHERN PLAINS LATE DAY 7
AND JUST BEYOND THIS FORECAST PERIOD...THE FIRST SUCH OUTBREAK IN
SEVERAL WEEKS.
CISCO/FLOOD
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