Prognostic Meteorological Discussion
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FXAK02 KWNH 301832
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT FRI SEP 30 2016

VALID 12Z TUE OCT 04 2016 - 12Z SAT OCT 08 2016

BASED ON THE CONSENSUS OF LATEST GUIDANCE RIDGING OVER THE
MAINLAND SHOULD REASSERT ITSELF BY THE LATTER HALF OF THE PERIOD
AS A DEEP MEAN LOW BECOMES ESTABLISHED OVER THE BERING SEA.  EARLY
IN THE FCST THERE IS A FAIR AMOUNT OF SPREAD WITH SOME SMALLER
SCALE DETAILS ALOFT OVER/NEAR THE MAINLAND AND ALSO WITH A SYSTEM
TRACKING TO THE S OF THE PANHANDLE.  OTHERWISE THE FOCUS WILL BE
ON TWO POTENTIALLY VERY DEEP NRN PAC-BERING SEA SYSTEMS.  AT THE
MOMENT GUIDANCE AGREEMENT APPEARS SOMEWHAT BETTER THAN AVG FOR A
DAYS 6-8 FCST.

FOR THE SYSTEM S OF THE PANHANDLE THERE IS STILL VERY WIDE
ENSEMBLE SPREAD... EASILY INCORPORATING OPERATIONAL SOLNS RANGING
FROM THE FARTHER NWD 00Z ECMWF AND INCREASINGLY SEWD 12Z GFS.
CONFIDENCE IS LOW WITH SPECIFICS OF INITIAL ENERGY FILTERING
THROUGH THE LONGER TERM RIDGE OVER THE MAINLAND.  AT THE VERY
LEAST THE 00Z/06Z GFS RUNS DID NOT COMPARE WELL TO OTHER GUIDANCE
WITH A DEFINED FEATURE NEAR THE BERING STRAIT.  THE 12Z GFS SFC
PATTERN LOOKS SOMEWHAT BETTER THOUGH ITS MID LVL DETAILS ARE STILL
A QUESTION MARK.

REGARDING NWRN PAC INTO ALEUTIANS/BERING SEA SYSTEMS... ENSEMBLE
MEANS ARE REMARKABLY SIMILAR WITH THE LEADING LOW THAT REACHES THE
BERING SEA BY DAY 6 THU.  OPERATIONAL RUNS ARE BEGINNING TO LATCH
ONTO A SECOND STRONG SYSTEM THAT COMES INTO THE PICTURE DAYS 7-8
FRI-SAT.  LATEST GEFS MEAN RUNS ONLY HINT AT A SECOND SYSTEM AT
THE SFC BUT IMPLY AN INFUSION OF ENERGY THAT MERGES WITH THE
LEADING FEATURE... LEADING TO CONTINUED GOOD AGREEMENT AMONG THE
MEANS THROUGH DAY 8 SAT.  00Z/06Z GFS RUNS WERE FASTER THAN
CONSENSUS WITH BOTH SYSTEMS.  THE 12Z GFS IS MUCH CLOSER TO THE
MAJORITY WITH BOTH FEATURES +INTO DAY 6 THU BEFORE FINALLY
TRENDING FASTER.  THE 00Z ECMWF COMPARES WELL TO CONSENSUS FOR THE
LEADING SYSTEM AND THE 00Z ECMWF MEAN IN WEAKER FORM SUPPORTS A
SCENARIO SIMILAR TO THE OPERATIONAL RUN FOR THE SECOND SYSTEM.

BASED ON GUIDANCE COMPARISONS AND 12Z GFS ADJUSTMENTS... THE
STARTING BLEND INCORPORATES ABOUT 70 PCT OPERATIONAL/30 PCT
ENSEMBLE GUIDANCE DISTRIBUTED AMONG THE 00Z ECMWF/12Z GFS RUNS AND
06Z GEFS/00Z ECMWF MEANS FROM DAY 4 TUE INTO DAY 5 WED.  WEIGHTING
ADJUSTS TOWARD A 50/50 MODEL/ENSEMBLE WEIGHTING BY THU BEFORE
LEANING ABOUT 70 PCT TO THE MEANS VS 30 PCT 00Z ECMWF FOR FRI-SAT.
 FOR THE SYSTEM S OF THE PANHANDLE THE RESULTING BLEND ENDS UP
WITH A SFC LOW TRACK CLOSER TO THE NRN SIDE OF THE OPERATIONAL
SPREAD BUT WITH A SUFFICIENTLY WEAK GRADIENT THAT LEADS TO A
PATTERN CLOSER TO OTHER SOLNS NEAR THE PANHANDLE.

RAUSCH

$$





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