Prognostic Meteorological Discussion
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FXAK02 KWNH 131834
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
134 PM EST SAT FEB 13 2016

VALID 12Z WED FEB 17 2016 - 12Z SUN FEB 21 2016

THE FCST PERIOD WILL FEATURE A COUPLE WELL DEFINED BERING
SEA/ALEUTIANS/NRN PAC SYSTEMS FEEDING INTO A LONG TERM E-CNTRL PAC
MEAN TROUGH.  THE LARGER PERCENTAGE OF GUIDANCE INDICATES THAT
MAINLAND ALASKA SHOULD REMAIN UNDER VARYING DEGREES OF MEAN
RIDGING... THOUGH WITH SOME UNCERTAINTY DUE TO THE AREA BEING
SOMEWHAT REMOVED FROM SYSTEMS FEEDING INTO THE E-CNTRL PAC TROUGH
AND PSBL INFLUENCE FROM HIGH LATITUDE FLOW.

FROM DAY 4 WED TO 12Z DAY 6 FRI... THE FCST STARTS WITH A 70/30
BLEND OF THE 00Z ECMWF/00Z ECMWF MEAN EARLY WED AND THEN STEADILY
DECREASES 00Z ECMWF WEIGHTING WHILE INCREASING THE ECMWF MEAN
COMPONENT PLUS ADDING SOME 06Z GEFS MEAN FROM EARLY THU ONWARD.
ECMWF-BASED PREFS AT THE START OF THE PERIOD REFLECT A DOMINANT
MAJORITY OF SOLNS BRINGING SHORT RANGE LOW PRES CLOSER TO THE SRN
ALASKA PANHANDLE THAN THE 00Z/06Z GFS-GEFS MEAN RUNS.  THE 12Z GFS
LOOKS MORE SIMILAR TO THIS IDEA.  AS A SFC LOW DEVELOPS/TRACKS TO
THE SE OF KODIAK ISLAND BY THU THERE HAS BEEN A NOTICEABLE SWD
TREND IN THE GUIDANCE VS 24 HRS AGO.  THE PREFERRED BLEND REFLECTS
THIS SWD ADJUSTMENT BUT NOT TO THE EXTENT SEEN IN THE GFS/CMC.
CONSIDERABLE ENSEMBLE MEMBER SPREAD PERSISTS FOR THIS SYSTEM.
THERE IS MODERATE CLUSTERING WITH THE SYSTEM REACHING THE SRN
BERING SEA/ALEUTIANS BY THU INTO FRI WITH THE ENSEMBLE MEANS
SHOWING THE MOST AGREEABLE EVOLUTION.

AFTER EARLY DAY 6 FRI VARIOUS ASPECTS OF THE 00Z ECMWF BEGIN TO
DEPART FROM ENSEMBLE MEAN CONSENSUS WITH OTHER OPERATIONAL MODEL
RUNS ALSO SUFFICIENTLY DIFFERENT TO FAVOR THE 00Z ECMWF MEAN/06Z
GEFS MEAN/00Z NAEFS MEAN EXCLUSIVELY... AND IN ORDER FROM HIGHEST
TO LOWEST WEIGHTING.  THE NERN PAC SYSTEM SHOULD WEAKEN WITH TIME
AS THE BERING SEA/ALEUTIANS SYSTEM TRACKING TO THE S OF THE
PENINSULA BECOMES THE DOMINANT FEATURE.  GIVEN THE TIME FRAME
INVOLVED THE CONSOLIDATED EVOLUTION OF THE ENSEMBLE MEANS IS
PREFERABLE WHILE OPERATIONAL MODEL RUNS INDICATE VARIOUS
POSSIBILITIES FOR SEPARATE INDIVIDUAL SFC LOW CENTERS.

OVER THE MAINLAND... MEANINGFUL UNCERTAINTIES ARISE FOR SPECIFICS
OF FLOW ALOFT BY MID-LATE PERIOD AFTER INITIAL MAINLAND RIDGING
WEAKENS.  THERE ARE INDICATIONS THAT ENERGY OVER/W OF THE CANADIAN
ARCHIPELAGO MAY EXTEND AT LEAST TOWARD THE NRN MAINLAND.  HOWEVER
LATEST GFS RUNS APPEAR TO BE ON THE EXTREME SIDE OF GUIDANCE WITH
THIS ENERGY.  ALSO LATE IN THE PERIOD TELECONNECTIONS RELATIVE TO
THE AMPLIFYING UPR TROUGH NEAR 160W LONGITUDE SUPPORT THE ENSEMBLE
MEAN IDEA OF THE WRN CANADA RIDGE BUILDING NWWD OVER THE MAINLAND.
 THIS SUGGESTS THE 00Z ECMWF IDEA OF BRINGING SOME SHEARED ENERGY
FARTHER SWD ACROSS THE MAINLAND MAY BE A LOW PROBABILITY SOLN AS
WELL.

RAUSCH

$$




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