000
FXUS02 KWNH 161245
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
844 AM EDT MON MAR 16 2009

VALID 12Z FRI MAR 20 2009 - 12Z MON MAR 23 2009

...00Z ECMWF ENSEMBLE MEAN AND 00Z CANADIAN/ECMWF ENSEMBLE 500 HPA
HEIGHT SPAGHETTIS AND SURFACE LOW POSITIONS UNAVAILABLE FOR THIS
DISCUSSION...

TELECONNECTIONS WITH A RELATIVELY STABLE POSITIVE ANOMALY SOUTH OF
THE UPPER ALEUTIANS TELECONNECTS TO MODEST TROUGHING OFFSHORE THE
WEST COAST AS WELL AS EASTERN CANADA...A POLAR VORTEX IN
NUNAVUT...ALONG WITH A SOUTHERN STREAM MOVING THROUGH NORTHWEST
MEXICO.  THIS IDEA IS REFLECTIVE IN THE LATEST 06Z GFS/00Z AND 06Z
GEFS ENSEMBLE MEAN SOLUTIONS.  THE 00Z ECMWF/00Z CANADIAN
SOLUTIONS ARE INTERESTING CONCERNING THEIR SIGNIFICANT
AMPLIFICATION AND STREAM PHASING ACROSS NORTH AMERICA.
INTERNALLY...THE CANADIAN AMPLIFICATION MAKES SOME SENSE...THOUGH
IT DOES NOT MATCH WELL WITH THE 00Z/06Z GEFS ENSEMBLE MEAN
SOLUTIONS ACROSS THE NORTHEAST PACIFIC WHICH IS PROBLEMATIC.  IN
THE CASE OF THE 00Z ECMWF...IT MANAGES TO AMPLIFY THE FLOW PATTERN
AROUND NORTH AMERICA WHILE AN INCREASINGLY ZONAL FLOW REGIME
BECOMES ESTABLISHED ACROSS THE EASTERN PACIFIC...A SOLUTION WHICH
DOES NOT MAKE MUCH SENSE.  FOUR TO FIVE DAYS AGO THE ECMWF TRIED A
SIMILAR AMPLIFICATION TO THE FLOW REGIME...ONLY TO BACK OFF AFTER
ONE OR TWO RUNS.  IT IS UNCLEAR IF THESE PROBLEMS ARE RELATED TO
CHANGES MADE IN THE ECMWF MODEL LAST WEEK.  SINCE THE POORLY
PERFORMING 00Z CANADIAN SUPPORTS THE 00Z ECMWF...WILL CONSIDER
THEIR SOLUTION A LOW PROBABILITY ALTERNATIVE SCENARIO /WHICH WOULD
HAVE SERVED US WELL WITH THE FORECAST ISSUED BY HPC FEBRUARY 24/.
IN ANY CASE...A 06Z GFS/06Z GEFS MEAN COMPROMISE WAS USED THROUGH
THE PERIOD...EXCEPT FOR EARLY THURSDAY WHEN THE 00Z ECMWF WAS
DEEMED MORE USABLE.  THIS SOLUTION KEPT GOOD CONTINUITY WITH NIGHT
SHIFT PRESSURE-WISE INTO THIS WEEKEND...BEFORE SPEEDING UP
CYCLONE/FRONTAL PROGRESSION BY NEXT MONDAY ACROSS THE
INTERMOUNTAIN WEST AND GREAT PLAINS...BUT HAS GREATER
REPERCUSSIONS IN THE ANTICIPATED TEMPERATURE PATTERN.

ROTH
$$