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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1845Z Dec 12, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 PM EST FRI DEC 12 2014

VALID 12Z TUE DEC 16 2014 - 12Z SAT DEC 20 2014

...STORMY WEATHER AGAIN UP INTO ALASKA...

MODELS AND ENSEMBLES STILL OFFER A REASONABLY SIMILAR LARGER SCALE
MEDIUM RANGE FLOW EVOLUTION THAT OFFERS AVERAGE OR BETTER FORECAST
CONFIDENCE AND CONTINUITY. THIS FLOW REMAINS HIGHLIGHTED ALOFT BY
AN UNSETTLING MEAN BERING SEA TROUGH THAT WEAKENS GRADUALLY OVER
TIME...AMPLE AND DEEPENING LEAD LOW ENERGIES CUTTING ACROSS THE
GULF OF ALASKA AND SPREADING HEAVIER PCPN/WINDS INTO SRN/SERN AK
UNDERNEATH GENERALLY BENIGN AND MODERATING WRN CANADIAN TO ALASKAN
INTERIOR MEAN RIDGING...AND SUBSEQUENT UPSTREAM VERY DEEP LOW
DEVELOPMENT AND WEATHER/WAVES OUT FROM THE NORTH-CENTRAL PACIFIC
TO THE ALEUTIANS THEN SW AK DAYS 6-8/NEXT THU-SAT.

THE DETERMINISTIC MODELS CHARACTERISTICALLY DIFFER WITH LESS
PREDICTABLE EMBEDDED AND LOCAL WEATHER FOCUSING SMALLER SCALE
EMBEDDED FEATURES...BUT THESE DIFFERENCES ARE SOMEWHAT REDUCED
COMPARED TO YESTERDAY. WPC PREFERENCE IS STILL PRIMARILY FOR AN
ENSEMBLE MEAN FORECAST APPROACH BUT A BIT (30%) DETERMINISTIC
GUIDANCE CAN BE WARRANTED TO PROVIDE A BIT MORE DETAIL WITHOUT
DEFLECTING FROM WPC CONTINUITY TOO MUCH. THE 00 UTC ECMWF/ECMWF
SEEM WELL CLUSTERED IN THE DAYS 4-6 TIMEFRAME...BUT A TRANSITION
TO THE WELL CLUSTERED 06 UTC GFS/12 UTC GFS HAS BEEN COORDINATED
WITH WFO ANCHORAGE TO OFFER A BIT MORE MAJOR LOW PROGRESSION OVER
THE ALEUTIANS TOWARD SW AK DAYS 7/8. WPC BLENDED THESE GUIDANCE
OPTIONS FOR PRIMARY DERIVATION OF THE WPC ALASKAN SURFACE
FRONTS/PRESSURES AND 500 MB PROGS ALONG WITH ASSOCIATED SENSIBLE
WEATHER GRIDS.

SCHICHTEL