604
FXUS02 KWNH 080900
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
400 AM EST SUN NOV 08 2009
VALID 12Z THU NOV 12 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 IS AGAIN FAIRLY EXTREME
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 LEANING AWAY FROM THE GFS IS THE MOST CONFIDENT
ASPECT OF THIS PART OF THE FCST. 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 ADVISORY ISSUED AT 0715Z. WITH ENSEMBLE
GUIDANCE THUS FAR CONSISTENT IN DOWNPLAYING POTENTIAL FOR ANY
STRONG WRN ATLC DEVELOPMENT... AND THE 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 THESE SOLNS MAY
PROVIDE ENOUGH OF A SIGNAL TO INCORPORATE MODEST WEIGHTING AS A
STARTING POINT. BY DAY 4 THU THE MANUAL FCST INCORPORATES A BLEND
TO YIELD A SOLN CONSISTENT WITH OPC PREFERENCES TOWARD A WEAKER
WRN ATLC SFC LOW SLIGHTLY S/SW OF THE 00Z ECMWF.
THE DAYS 3-4 WED-THU FCST STARTS WITH A BLEND OF THE 00Z ECMWF AND
00Z GEFS/12Z ECMWF ENSEMBLE MEANS TO PROVIDE A DECENT
REPRESENTATION OF CONSENSUS AND YIELD THE DESIRED SOLN OVER THE
WRN ATLC. SOME OF THE 00Z ECMWF WEIGHTING WAS REPLACED WITH THE
12Z/7 ECMWF DAYS 5-7 FRI-SUN AS THE 00Z ECMWF SOLN BECOMES MORE
QUESTIONABLE.
RAUSCH
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