PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
829 AM EST TUE JAN 20 2009
 
VALID 12Z SAT JAN 24 2009 - 12Z TUE JAN 27 2009
 
MULTI-DAY MEANS FROM 00Z GFS/ECMWF/GEFS MEAN RUNS DEPICT TWO
SIGNIFICANT HGT ANOMALY CENTERS THAT SHOULD HAVE AN INFLUENCE ON
NORTH AMERICAN FLOW BY THE LATTER HALF OF THE FCST PERIOD.  OVER
THE PAC A STRONG POSITIVE ANOMALY CENTER IS FCST APPROXIMATELY
BETWEEN ALASKA AND HAWAII.  TELECONNECTIONS RELATIVE TO THIS
FEATURE FAVOR A FAIRLY DEEP TROF WITH AN AXIS SOMEWHERE OVER THE
INTERIOR WEST OR PAC NW COAST DEPENDING ON THE POSN OF THE
UPSTREAM RIDGE.  MEANWHILE A STRONG NEGATIVE HGT ANOMALY EXPECTED
OVER THE NERN ATLC TELECONNECTS TO A BROAD MEAN TROF ORIENTED OVER
E-CNTRL NOAM... WITH ABOVE OR WELL ABOVE NORMAL HGTS FROM THE EAST
COAST INTO THE WRN ATLC.

GUIDANCE IS STILL HAVING DIFFICULTIES IN HANDLING FLOW OVER
ALASKA/NWRN CANADA IN THE SHORT RANGE SO THERE REMAINS SOME
UNCERTAINTY IN THE FCST AS OF DAY 3 FRI.  00Z/06Z GFS RUNS ARE
ONCE AGAIN MORE RELUCTANT TO CLOSE OFF AN UPPER HIGH OVER OR NEAR
THE NRN AK COAST VERSUS MOST OTHER GUIDANCE... SO THEIR SOLNS ARE
CONSIDERED AMONG THE LESS LIKELY ONES ACROSS SRN CANADA AND NRN
CONUS LATE THIS WEEK INTO THE WEEKEND.  THERE IS STILL FAIR
AGREEMENT THAT STRENGTHENING OF THE ERN PAC RIDGE SHOULD ENCOURAGE
DEVELOPMENT OF A TROF OVER THE WEST BY AROUND DAY 5 SUN.  GFS RUNS
MAY BE BRINGING TOO MUCH SWRN CANADA ENERGY INTO THE NWRN STATES
DUE TO ISSUES EARLIER IN THE PERIOD.  

MODEL AND ENSEMBLE SPREAD SHOWS A MORE DRAMATIC INCREASE BY DAYS
6-7 MON-TUE.  WHAT AGREEMENT THAT DOES EXIST AMONG 00Z
GEFS/ECMWF/CANADIAN ENSEMBLES WOULD INDICATE THAT UPSTREAM PAC
FLOW SHOULD APPROACH THE WEST COAST EARLIER THAN FCST BY 00Z/06Z
GFS RUNS... THUS KICKING THE WRN CONUS TROF EWD FASTER THAN THE
GFS.  THIS IS REFLECTED IN THE 00Z GEFS MEAN WHOSE TROF AXIS IS
FAIRLY CLOSE TO THE 00Z ECMWF AND SLIGHTLY FASTER 12Z/19 EC RUNS
THAT ARE OVER THE PLAINS AS OF EARLY DAY 7 TUE.  00Z ECMWF
ENSEMBLE MEAN PROGRESSION IS AT LEAST AS FAST AS THE 12Z/19 EC. 
AS OF EARLY TUE INDIVIDUAL GEFS/EC/CMC ENSEMBLE MEMBERS SHOW NO
WELL DEFINED CLUSTERING OF SFC WAVES... WITH A FAIRLY EVEN
SCATTERING FROM THE SRN HALF OF THE PLAINS TO THE ERN SLOPES OF
THE CNTRL-SRN APLCHNS. 

LATE PERIOD EVOLUTION OF ECMWF RUNS AND VARIOUS ENSEMBLE MEANS
OVER THE ERN PAC/WRN CONUS SEEMS TO GO ALONG WITH ERN PAC/WRN NOAM
TELECONNECTIONS BETTER THAN THE OPERATIONAL GFS RUNS... WHILE A
COMPROMISE AMONG THOSE NON-GFS SOLNS SHOULD PROVIDE A REASONABLE
COMPROMISE FOR RESOLVING VERY UNCERTAIN TIMING DIFFS OVER THE
CNTRL-ERN CONUS.  THUS THE DAYS 6-7 MON-TUE FCST STARTS WITH A
50/30/20 BLEND OF THE 00Z ECMWF/00Z GEFS MEAN/00Z EC ENS MEAN...
WITH DAY 7 FURTHER ADJUSTED TO A 00Z EC AND 12Z/19 EC COMPROMISE
TO ARRIVE AT AN INTERMEDIATE FRONTAL POSN OVER THE ERN HALF OF THE
CONUS.  A 70/30 BLEND OF THE EC/EC MEAN PROVIDES A FAIR
REPRESENTATION OF CONSENSUS WITH THE DAYS 3-5 FRI-SUN FCST THAT IS
DOMINATED BY COLD HIGH PRESSURE BUILDING INTO THE CNTRL-ERN STATES
AND LEADING LOW PRESSURE/COLD FRONT.

RAUSCH
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