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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1859Z Apr 12, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT SAT APR 12 2014

VALID 12Z WED APR 16 2014 - 12Z SUN APR 20 2014

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

THE GOOD NEWS IS THAT GUIDANCE REMAINS QUITE COMPATABLE WITH
DEPICTION OF THE LARGER SCALE MEDIUM RANGE FLOW EVOLUTION.  THIS
INCLUDES DEVELOPMENT OF AMPLIFIED/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.  THE
BAD NEWS IS THAT SMALLER SCALE SYSTEMS AND ASSOCIATED
SYSTEM/STREAM INTERACTIONS EMBEDDED WITHIN THIS FLOW HAS BEEN
INCONSISTENTLY DEPICTED BY GUIDANCE...ESPECIALLY WITH TRANSITION.

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 5-8 / THU-NEXT SUN.  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 DEEP SYSTEM THEN HOLDS OFFSHORE WITH MUCH LESSER
EFFECT INLAND THROUGH SRN/SERN AK INTO THE INTERIOR AS SHIELDED BY
THE LINGERING MID-UPPER LEVEL MEAN RIDGE.

GIVEN SMALLER SCALE UNCERTAINTY...WPC ALASKAN MEDIUM RANGE SURFACE
FRONTS/PRESSURES AND 500 MB PROGS ALONG WITH OUR SENSIBLE WEATHER
GRIDS HAVE BEEN AGAIN PRIMARILY DERIVED FROM A COMPOSITE BLEND OF
THE GFS/ECMWF AND GFS/ECMWF ENSEMBLE MEANS...LEANING MORE ON THE
MEANS ESPECIALLY BY DAYS 6-8 CONSISTENT WITH INCREASING
UNCERTAINTY TO EMPHASIZE THE MORE PREDICTABLE FORECAST COMPONENTS.
 THIS FORECAST PLAN MAINTAINS GOOD WPC CONTINUITY DESPITE A
PATTERN WITH LESS THAN STELLAR EMBEDDED SYSTEM CONTINUITY.

SCHICHTEL