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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1816Z Nov 22, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
116 PM EST SAT NOV 22 2014

VALID 12Z WED NOV 26 2014 - 12Z SUN NOV 30 2014

THE 22/00Z ECENS/GEFS BLEND CAPTURES THE BROAD-SCALE EVOLUTION OF
THE NORTHERN PACIFIC FLOW PATTERN FOR DAYS 4-8. THE SOUTHWARD
DISPLACEMENT OF THE UPPER-LEVEL PACIFIC JET---AND MORE
IMPORTANTLY...THE MODIFIED MARITIME POLAR AIRMASS 'DRAPE'
OVERSPREADING A LARGE MAJORITY OF THE NORTHERN PACIFIC OCEAN ARE
THE KEY FEATURES ANCHORING THE PATTERN THIS MEDIUM RANGE PERIOD.
THESE FEATURES REMAIN IN PLACE---AND ALTHOUGH THE UPPER-LEVEL JET
STREAM ATTEMPTS TO PRODUCE AMPLITUDE IN THE EAST CENTRAL PACIFIC
EARLY IN THE PERIOD---WITH A SUBTROPICAL CONNECTION---THE
LOWER-LEVEL SUPPORT IS NOT THERE TO CHANGE THE PATTERN OVER
NORTHWEST NORTH AMERICA---INCLUDING ALASKA. THAT SAID...THE
MODIFIED-ARCTIC DRAPE STANDS FIRM ACROSS THE YUKON AND EASTERN
INTERIOR OF ALASKA...AND ANCHORS THE NORTHERN PERIPHERY OF A
LONGWAVE RIDGE IN WESTERN CANADA AND THE EXTREME NORTHERN ALASKA
PANHANDLE.

THE NEXT FORECAST CHALLENGE---TROUGH DISPERSION IN THE BERING SEA
AND ITS GRADUAL EASTWARD MIGRATION ACROSS THE ALEUTIANS AND INTO A
POSITION BY DAY 8---THAT REMAINS NEARER TO ITS 'CLIMO' POSITION
ALONG 150W-155W LONGITUDE FOR LATE NOVEMBER. PRIOR TO ITS
EXTENSION INTO THE PACIFIC/WESTERN GULF...THERE ARE SEVERAL
SHORTWAVES THAT ROTATE COUNTER-CLOCKWISE ACROSS THE BERING SEA AND
BRUSH THE YUKON DELTA BEFORE MIGRATING WESTWARD INTO THE WEST
CENTRAL BERING SEA.

THE 22/00Z DETERMINISTIC GUIDANCE SPREAD IN THE BERING SEA IS
LARGE---YET THE ECENS/GEFS MEANS AGREE ON A VERY GRADUAL EASTWARD
DRIFT OF THE BROAD CYCLONIC FLOW THROUGH TIME...FROM 53N 174E (DAY
4) 54N 156W (DAY8). WHAT THIS SUGGESTS IS A SUPPRESSION OF THE
'AVERAGED' PACIFIC STORM TRACK...ALONG AND SOUTH OF 50N. THIS MAY
NOT BE AN ACTIVE PATTERN FOR MUCH OF 'THE 49TH STATE'...BUT WILL
BE DOWNSTREAM---FOR THE LOWER 48'S WEST COAST.

VOJTESAK