Prognostic Meteorological Discussion
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FXAK02 KWNH 271903
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
202 PM EST MON FEB 27 2017

VALID 12Z FRI MAR 03 2017 - 12Z TUE MAR 07 2017

THE MAJORITY OF GUIDANCE AGREES FAIRLY WELL IN SHOWING A MILD
RETROGRESSION OF LARGE SCALE FEATURES... WITH A STRONG CNTRL
BERING SEA RIDGE/UPR HIGH DRIFTING TO THE WRN BERING SEA/ERN
SIBERIA AND ALLOWING FOR A DEEPENING MEAN TROUGH TO EVOLVE OVER
MAINLAND ALASKA AND THE NERN PAC/GULF OF ALASKA.  AMONG INDIVIDUAL
SOLNS THERE IS STILL SOME DISAGREEMENT OVER EXTENT OF WWD MOTION
FOR THE UPR RIDGE.  OTHER QUESTION MARKS EXIST FOR SHRTWV DETAILS
EARLY IN THE PERIOD AND SPECIFICS OF NERN PAC/GULF OF ALASKA LOW
LOW PRESSURE THAT SHOULD BE DEEPENING LATE IN THE PERIOD.

DURING DAYS 4-5 FRI-SAT THE PRIMARY DIFFS ARE WITH SHRTWV ENERGY
FLOWING BTWN THE BERING SEA/ERN SIBERIA RIDGE AND DEEP UPR LOW TO
THE NE OF THE MAINLAND.  THE RELATIVELY SMALL SCALE OF INDIVIDUAL
SHRTWVS TYPICALLY LEADS TO LOW PREDICTABILITY FOR SPECIFICS EVEN
IN THE EARLY EXTENDED TIME FRAME.  FOR THIS PART OF THE FCST THE
INITIAL BLEND USED THE 00Z ECMWF/GFS/CMC TO REPRESENT COMMON
ASPECTS OF THE FCST SFC/ALOFT WITH BETTER DEFINITION THAN THE
ENSEMBLE MEANS.

BY DAYS 5-7 SUN-TUE THE MOST SIGNIFICANT DISCREPANCIES INVOLVE
BERING SEA/SIBERIA RIDGE POSN AND MAINLAND/NERN PAC TROUGHING PLUS
DETAILS OF ASSOC GULF OF ALASKA SFC LOW EVOLUTION.  FOR THE RIDGE
THE LATEST GEFS/ECMWF/CMC ENSEMBLE MEANS OFFERED THE MOST SUPPORT
FOR A FARTHER W POSN THAN 00Z/06Z/12Z GFS RUNS AND PERHAPS THE 00Z
CMC.  WHILE THERE IS CONSIDERABLE SPREAD IN DETAILS FOR THE
MAINLAND/NERN PAC TROUGH... THE ENSEMBLE MEANS ARE SHOWING A
NOTICEABLY DEEPER SIGNAL ALOFT WITH GULF OF ALASKA LOW PRES ALSO
TRENDING DEEPER.  OVER THE PAST 1-2 DAYS ECMWF MEAN RUNS HAVE BEEN
MORE CONSISTENT WITH THE OVERALL RIDGE/TROUGH PATTERN AND MORE
STEADY WITH THE DEEPENING TREND FOR THE UPR TROUGH/SFC LOW PRES.
BASED ON THESE TRENDS IT SEEMED REASONABLE TO START OUT WITH AN
UPR TROUGH/SFC LOW DEPTH BTWN OPERATIONAL GUIDANCE AND THE WEAKER
ENSEMBLE MEANS AS THE BEST WAY TO BALANCE THE AGREEABLE MEAN
PATTERN AND DETAIL UNCERTAINTY.  DUE TO THE BETTER STABILITY OF
THE ECMWF MEANS FOR THE OVERALL PATTERN THE ENSEMBLE MEAN
COMPONENT OF THE FCST USED A HIGHER WEIGHTING OF THE 00Z ECMWF
MEAN VS THE 06Z GEFS MEAN... WHILE THE 00Z ECMWF/GFS/CMC PROVIDED
THE OPERATIONAL INPUT.  VARIOUS SCENARIOS ARE PSBL FOR EXACT
EVOLUTION OF THE GULF OF ALASKA SFC LOW INCLUDING IN-PLACE
DEEPENING (00Z CMC) OR MULTI-LOW INTERACTION INCLUDING A LEADING
FEATURE NEAR HAIDA GWAII (12Z GFS) IN RESPONSE TO DIGGING
TROUGH/CLOSED LOW ENERGY... OR INTERACTION WITH A MID-LATITUDE PAC
WAVE APPROACHING FROM THE SW (00Z GFS/ECMWF/ECMWF MEAN).  WHICH
EVOLUTION ULTIMATELY OCCURS WILL IMPACT THE AMOUNT OF MOISTURE
THAT REACHES THE SRN COAST/PANHANDLE REGION.

RAUSCH

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