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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2030Z Dec 26, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
330 PM EST FRI DEC 26 2014

VALID 12Z TUE DEC 30 2014 - 12Z SAT JAN 03 2015

AN ACTIVE TROUGH REMAINS IN THE FORECAST OVER THE WESTERN BERING
SEA AND ALEUTIANS. A RELEASE OF ARCTIC AIR INTO THE LOWER 48
SPREADS WESTWARD ACROSS THE PANHANDLE AND INTO THE FAR
EASTERN/NORTHEASTERN GULF OF ALASKA. HIGH PRESSURE PREVAILS ALONG
120W-130W FROM THE ARCTIC CIRCLE SOUTHWARD INTO
THE PACIFIC NORTHWEST STATES.

THE SUBTLE 'KEY' IN THE MEDIUM RANGE PATTERN---IS THE
NORTHEASTWARD PROGRESSION OF THE UPPER-LEVEL TROUGH AND ITS
'ABILITY' TO EJECT MID-LEVEL ENERGY---SOUTHEASTWARD---ACROSS THE
SOUTHEAST BERING SEA...EASTERNMOST ALEUTIANS AND INTO THE
NORTHWEST GULF OF ALASKA.

IT APPEARS THE ECMWF ENSEMBLE MEAN HAS A HANDLE ON THE PATTERN.
THE PAST THREE CYCLES DO NOT BUDGE WITH THE RIDGE POSITION IN
NORTHWESTERN NORTH AMERICA AND NORTHEAST ALASKA. AT THE SURFACE
THE MODIFIED ARCTIC FRONT EXTENDS INTO A GOOD PORTION OF THE
EASTERN HALF OF THE GULF OF ALASKA DURING THE ENTIRE MEDIUM RANGE
PERIOD. WPC USED A 40/30/30 BLEND OF 26/00Z ECMWF
ENSEMBLE...25/12Z ECMWF ENSEMBLE...AND THE 26/00Z ECMWF
DETERMINISTIC RUN TO DERIVE THE HEIGHT/MSLP PATTERN AND GRIDDED
FORECASTS. THIS BLEND PLACES ENERGY NORTHWARD THROUGH THE ENTIRE
EASTERN BERING SEA AND ADDS SOME DETAIL IN THE WIND FIELDS. IN
ADDITION...IT ALLOWS A SURFACE TROUGH/STATIONARY FRONT TO FORM
OVER THE PANHANDLE WITHIN A WEAKENED/MODIFIED CREASE IN THE
SURFACE RIDGE.

VOJTASEK/BURKE