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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1708Z Apr 13, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
108 PM EDT SUN APR 13 2014

VALID 12Z THU APR 17 2014 - 12Z MON APR 21 2014

...PATTERN OVERVIEW...GUIDANCE AND UNCERTAINTY
ASSESSMENT...SENSIBLE WEATHER HIGHLIGHTS...

GUIDANCE REMAINS QUITE COMPATABLE WITH DEPICTION OF THE LARGER
SCALE MEDIUM RANGE FLOW EVOLUTION.  THIS INCLUDES DEVELOPMENT OF
AMPLIFIED/QUASI OMEGA-STYLE MID-UPPER LATITUDE FLOW FROM NE ASIA
TO THE BERING SEA THROUGH MIDWEEK...WITH LEAD RIDGING CENTERED
OVER THE INTERIOR AND LEAD TROUGH SYSTEM ENERGIES OVER THE
E-CENTRAL GULF OF AK.  DESPITE AMPLITUDE...THIS PATTERN SEEMS
SLOWLY PROGRESSIVE IN MOST GUIDANCE INTO NEXT WEEKEND.  SMALLER
SCALE SYSTEMS AND ASSOCIATED SYSTEM/STREAM INTERACTIONS EMBEDDED
WITHIN THIS FLOW HAS BEEN INCONSISTENTLY DEPICTED BY
GUIDANCE...ESPECIALLY WITH TRANSITIONS.

WHILE EMBEDDED DETAILS REMAIN UNCERTAIN IN THE NORTH...ARCTIC
IMPULSES ALOFT GRADUALLY WORK THROUGH THE NORTH SLOPE AND INTO
INTERIOR RIDGING BY LATE WEEK LEADING INTO AT LEAST SOME MEAN
WEAKNESS INTO NEXT WEEKEND AS PER WPC 500 MB PROGS.

MEANWHILE UNDERNEATH...A POTENT TROUGH/CLOSED LOW ENERGIES
FOCUSING EARLY-MID WEEK NEAR THE ALEUTIANS WORK STEADILY INTO THE
GULF OF AK DAYS 4-8 / THU-NEXT MON.  THIS SYSTEM OFFERS WELL
ORGANIZED LOW DEVELOPMENT AS PER WPC PROGS WITH MODEST PCPN
POTENTIAL SPREADING FROM THE ALEUTIANS AND SW AK INTO A QUITE
UNSETTLED GULF WHERE ENERGIES COMBINE WITH THE LEAD SYSTEM
ENVIRONMENT.  THE COMPLEX DEEP SYSTEM THEN HOLDS OFFSHORE WITH
MUCH LESSER EFFECT INLAND THROUGH SRN/SERN AK INTO THE INTERIOR. 

LATER UPSTREAM...MODELS AND ENSEMBLES REASONABLY AGREE TO BRING
YET A CLOSED TROUGH/LOW CENTERED ALONG AND JUST TO THE SOUTH OF
THE WRN ALEUTIANS IN ABOUT A WEEK.  THIS WOULD AGAIN LEAD TO QUITE
UNSETTLED WEATHER WITH WELL ORGANIZED WINDY/RAINY CONDITIONS OVER
THE AREA.

MANUAL FORECASTER ADJUSTMENTS INSURE CLOSED SYSTEM DEEPNESS ALOFT
AND AT LOWER ATMOSPHERIC LEVELS CONSISTENT WITH AMPLE DYNAMIC
SUPPORT WITH BOTH OF THESE CLOSED STORMS.


GIVEN SMALLER SCALE UNCERTAINTY...WPC ALASKAN MEDIUM RANGE SURFACE
FRONTS/PRESSURES AND 500 MB PROGS ALONG WITH OUR SENSIBLE WEATHER
GRIDS HAVE BEEN REMAIN PRIMARILY DERIVED FROM A COMPOSITE BLEND OF
THE 06 UTC GEFS MEAN AND 00 UTC ECMWF ENSEMBLE MEAN CONSISTENT
WITH INCREASING UNCERTAINTY TO EMPHASIZE THE MORE PREDICTABLE
FORECAST COMPONENTS.  THIS FORECAST PLAN MAINTAINS DECENT WPC
CONTINUITY DESPITE A PATTERN WITH LESS THAN STELLAR EMBEDDED
SYSTEM CONTINUITY.

SCHICHTEL