Prognostic Meteorological Discussion
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FXAK02 KWNH 211833
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT THU MAY 21 2015

VALID 12Z MON MAY 25 2015 - 12Z FRI MAY 29 2015

OVERALL THE LATEST GUIDANCE SUGGESTS MAINTENANCE OF MEAN RIDGING
OVER WRN CANADA AND MAINLAND ALASKA WHILE TROUGHING WITH ONE OR
MORE EMBEDDED UPR LOWS SHOULD EXIST UPSTREAM.  HOWEVER WITHIN THE
EXPECTED MEAN PATTERN THERE ARE MEANINGFUL DETAIL DIFFS THAT MAY
TAKE SOME TIME TO BE RESOLVED.

OVER THE MAINLAND AND VICINITY THE PRIMARY ISSUES ARE WITH THE
ULTIMATE EVOLUTION OF SHRTWV ENERGY NEARING THE SRN
COAST/PENINSULA AS OF THE START OF THE PERIOD MON AND THEN THE
SHAPE/POSN OF RIDGING ALOFT.  IN BOTH RESPECTS OPERATIONAL RUNS
SHOW RATHER POOR AGREEMENT/CONTINUITY BY MID-LATE PERIOD.  ON THE
OTHER HAND RECENT RUNS OF BOTH THE GEFS AND ECMWF MEANS HAVE BEEN
MORE CONSISTENT AND SIMILAR WITH THE AXIS/ORIENTATION... AND FOR
THE MOST PART STRENGTH... OF THE RIDGE ALOFT.  THUS WOULD FAVOR
THE ENSEMBLE MEANS BY A CONSIDERABLE DEGREE OVER ANY PARTICULAR
OPERATIONAL SOLN OVER/NEAR THE MAINLAND FOR MOST OF THE FCST
PERIOD.

CONFIDENCE IS LOWER FROM THE PACIFIC INTO THE BERING SEA.  THERE
IS ALREADY SPREAD AT THE START OF THE PERIOD WITH LEADING WRN
ALEUTIANS LOW PRES.  THE 00Z ECMWF AND 06Z GFS CLUSTER WELL WITH
LATEST ENSMEANS AS OF MON SO GREATER WEIGHTING OF THOSE TWO
OPERATIONAL RUNS APPEARS REASONABLE FOR THE FIRST DAY OF THE
PERIOD.  NOTE THAT OVER THE PAST 24 HRS THE ECMWF HAS BEEN MORE
STABLE AS OF MON WITH 00Z AND 12Z GFS RUNS FASTER THAN THE
AFOREMENTIONED CONSENSUS.  SOLNS DIVERGE FROM EARLY DAY 5 TUE
ONWARD THOUGH.  IN ADDITION GUIDANCE IS SPLIT AS TO THE POTENTIAL
INTERACTION BTWN THIS LEADING SYSTEM AND A TRAILING SYSTEM
APPROACHING FROM THE WRN PAC.  THE ENSMEANS SHOW A CONSOLIDATED
SYSTEM TRACKING NEAR THE ALEUTIANS WHILE MOST OPERATIONAL RUNS
DEPICT GREATER SEPARATION WITH A MORE SUPPRESSED TRACK FOR THE PAC
SYSTEM.  HOWEVER THE 12Z GFS DOES BRING THE SFC LOW CLOSE TO THE
ALEUTIANS BY LATE NEXT WEEK.  GUIDANCE SPREAD COMBINED WITH
AFOREMENTIONED ENSMEAN PREFS FOR THE MAINLAND FAVOR EMPHASIZING
THE 06Z GEFS/00Z ECMWF MEANS FOR DAYS 5-8 TUE-FRI... WITH THE
UNDERSTANDING THAT THE VARIOUS SOLNS WITHIN THE OVERALL ENVELOPE
ARE STILL PLAUSIBLE.

RAUSCH

$$




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