631
FXUS02 KWBC 081831
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
130 PM EST SUN NOV 08 2009
VALID 12Z WED NOV 11 2009 - 12Z SUN NOV 15 2009
THE MOST AGREEABLE ASPECT OF THE MEDIUM RANGE FCST CONTINUES TO BE
WITH A STRONG CORE OF LOW HGTS ALOFT MOVING TOWARD AND SETTLING
OVER ALASKA WITH A BROAD MEAN TROF BECOMING ESTABLISHED OVER THE
NERN PACIFIC. FAST PACIFIC FLOW IS FCST TO STREAM INTO NOAM FROM
AROUND FRI ONWARD. TELECONNECTIONS RELATIVE TO THE STRONG CORE OF
NEGATIVE HGT ANOMALIES FCST TO RESIDE OVER ALASKA BY THE LATTER
HALF OF THE PERIOD FAVOR PROGRESSIVE SRN CANADA/NRN CONUS FLOW
WITH A HINT OF A MEAN TROF OVER ERN CANADA INTO THE GRTLKS/UPR MS
VALLEY... AND A MODEST MEAN TROF FROM NEAR THE SRN ROCKIES INTO
NWRN MEXICO. THE 00Z GFS AND ECMWF PROVIDE TWO VERY DIFFERENT
EVOLUTIONS OF THE INCOMING PACIFIC FLOW WITH THE GFS BRINGING IT
EWD ALONG THE US-CANADIAN BORDER WHILE THE ECMWF AMPLIFIES ENERGY
INTO THE SRN ROCKIES BY DAY 7 SUN. THE UKMET/CANADIAN ARE
ACTUALLY FASTER/FLATTER VERSIONS OF THE GFS. PREVIOUS ECMWF RUNS
ALONG WITH 00Z GEFS/12Z ECMWF ENSEMBLES DO NOT PROVIDE MUCH
SUPPORT FOR THE 00Z ECMWF SCENARIO... BUT CONSISTENT WITH
TELECONNECTIONS DO INDICATE SOME ENERGY SETTLING INTO THE WRN
CONUS/NWRN MEXICO. ANOTHER QUESTIONABLE ASPECT OF THE 00Z ECMWF
IS A DEEPENING SYSTEM WHICH THE MODEL BRINGS ACROSS THE NERN
PACIFIC FRI-SAT AND DOES NOT COMPARE WELL TO LATEST ENSEMBLES.
THERE IS ALSO A DECENT AMOUNT OF SPREAD WITH THE ULTIMATE
EVOLUTION OF ERN PAC ENERGY TRACKING INTO WRN NOAM DURING THE
FIRST HALF OF THE FCST. THE 00Z GFS SEEMS AN OUTLIER COMPARED TO
OTHER GUIDANCE REGARDING THE STRENGTH OF HGT FALLS PASSING THRU
THE UPR MS VALLEY/GRTLKS DURING THE FRI NIGHT-SAT TIME FRAME... SO
BLENDING AWAY FROM THE GFS SEEMS MORE REASONABLE CONSIDERING THE
AMBIENT LEAD RIDGING ALOFT. OTHERWISE THERE IS ENOUGH
MODEL/ENSEMBLE SPREAD AND RUN TO RUN INCONSISTENCY REGARDING
PROGRESSION OF NRN STREAM FLOW ALONG THE US-CANADIAN BORDER TO
PRECLUDE ENDORSEMENT OF ANY PARTICULAR SOLN.
DURING DAYS 3-4 WED-THU FROM THE GULF OF MEXICO INTO THE WRN
ATLC... CONFIDENCE REMAINS LOW WITH THE EXTRATROPICAL EVOLUTION OF
HURCN IDA... AND POSSIBLE WRN ATLC DEVELOPMENT THAT IS DEPICTED IN
THE 00Z GFS/ECMWF/CMC. THE MANUAL FCST REFLECTS THE TPC TRACK FOR
IDA GIVEN BY THE SPECIAL 18Z ADVISORY. WITH ENSEMBLE GUIDANCE
THUS FAR CONSISTENT IN DOWNPLAYING POTENTIAL FOR ANY STRONG WRN
ATLC DEVELOPMENT... AND THE 00Z UKMET/NOGAPS ALSO PROGRESSIVE WITH
SHRTWV ENERGY REACHING THE WRN ATLC EARLY IN THE FCST... IT IS
DIFFICULT TO PLACE TOO MUCH CONFIDENCE IN THE GFS/ECMWF/CMC YET.
HOWEVER TAKEN AS A WHOLE THE SOLNS WE NOW HAVE MAY PROVIDE ENOUGH
OF A SIGNAL TO INCORPORATE MODEST WEIGHTING AS A STARTING
POINT...KEEPING IN MIND CONTINUITY AMID UNCERTAINTY...WITH NEWER
12Z GUIDANCE STILL OFFERING A WIDE ARRAY OF SOLUTIONS. ACCORDINGLY
BY DAY 4 THU...THE HPC MANUAL FCST STILL INCORPORATES A BLEND TO
YIELD A SOLN CONSISTENT WITH OPC PREFERENCES TOWARD A WEAKER WRN
ATLC SFC LOW.
THE FINAL HPC FCST EDITION REMAINS PRIMARILY DERIVED FROM A BLEND
OF 60% 00Z GFS ENSEMBLE MEAN AND 40% 00Z GFS DAYS 3-7. THIS
SOLUTION MAINTAINS GOOD HPC CONTINUITY AMID STILL VARIED NEWER 12Z
MODEL AND ENSEMBLE GUIDANCE. THIS SOLUTION STILL SEEMS TO PROVIDE
A DECENT REPRESENTATION OF CONSENSUS AND YIELD THE DESIRED SOLN
OVER THE WRN ATLC AND UPSTREAM FROM THE ERN PAC INTO NOAM.
RAUSCH/SCHICHTEL
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