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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1803Z Dec 15, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
103 PM EST MON DEC 15 2014

VALID 12Z FRI DEC 19 2014 - 12Z TUE DEC 23 2014

...STORMY CONDITIONS UP TOWARD ALASKA WITH SEVERAL BIG LOWS...

WPC ALASKAN MEDIUM RANGE SURFACE FRONTS/PRESSURES AND 500 MB PROGS
ALONG WITH ASSOCIATED SENSIBLE WEATHER GRIDS HAVE BEEN PRIMARILY
DERIVED FROM A BLEND OF THE 00 UTC GFS/ECMWF ENSEMBLE MEANS.
LEANED HEAVIER ON THE ECMWF ENSEMBLE MEAN IN THIS BLEND TO PROVIDE
BETTER WPC CONTINUITY. THE DETERMININISTIC MODELS AGAIN OFFER TOO
MUCH RUN TO RUN CONTINUITY ISSUES WITH EMBEDDED SMALLER SCALE
SYSTEMS...BUT BEYONFD THAT FEED WELL INTO THE OVERALL LARGER SCALE
PATTERN EVOLUTION AS DEPICTED BY THE COMPATABLE GFS/ECMWF ENSEMBLE
MEANS.

AS DESCRIBED IN A SIMILAR FASHION YESTERDAY...THE UPPER PATTERN
ACROSS AK STARTS FAIRLY BLOCKY IN NATURE AT THE HIGHER LATITUDES.
THIS SECTION OF THE STATE IS FORECAST TO FEATURE A SERIES OF
SMALLER-SCALE SHORTWAVES COMPROMISED OF NUMEROUS MERGERS/SPLITS
WHICH WILL BE DIFFICULT TO RESOLVE INTO THE MEDIUM RANGE. TO THE
SOUTH...THE FLOW IS EXPECTED TO BE MODESTLY PROGRESSIVE EVEN WITH
AMPLITUDE THAT FEATURES A SERIES OF WELL-DEFINED UPPER TROFS
MOVING TOWARD THE GULF OF AK. THE LEAD SYSTEM WILL CONSIST OF AN
INITIALLY STRONG CLOSED LOW SLOWLY MIGRATING EASTWARD TOWARD
SOUTHEASTERN AK INTO LATE WEEK. AS THE LEAD SYSTEM GRADUALLY
SHEARS WHILE MOVING INLAND...ADDITIONAL HEIGHT FALLS WILL SLIDE
EASTWARD WITHIN THE STRONG PACIFIC JET. THIS WILL HELP DRIVE
ANOTHER IMPRESSIVE UPPER LOW JUST SOUTH OF THE ALEUTIANS LATE THIS
WEEK AND OUT ACROSS THE NRN GULF OF AK INTO EARLY NEXT WEEK WHOSE
DEEP SURFACE SYSTEM WILL AGAIN SPREAD A LARGE AREA OF HIGH
PCPN/WINDS/WAVES. YET ANOTHER BIG SYSTEM MAY BE SLATED TO WORK
INTO THE BERING SEA/ALEUTIANS BY EARLY NEXT WEEK IN AMPLIFIED
UPSTREAM FLOW.

SCHICHTEL