Prognostic Meteorological Discussion
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FXAK02 KWNH 021847
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 PM EDT TUE JUN 02 2015

VALID 12Z SAT JUN 06 2015 - 12Z WED JUN 10 2015

THE 2/00Z ECENS/GEFS MEANS AND OPERATIONAL ECMWF WERE IN
REASONABLE AGREEMENT AND ACCEPTABLE PIECES OF GUIDANCE TODAY ---
FOR USE IN THE WPC DAYS 4-8 SURFACE AND 500MB GRAPHICS. WHAT HAS
BEEN GENERALLY A PERIOD OF UNSETTLED WEATHER IN THE
ALEUTIANS...WEST COAST...SOUTHERN BERING AND SOUTHERN COAST WILL
CONTINUE TO MIGRATE EASTWARD INTO THE PANHANDLE---CULMINATING IN A
DAY 6-8 BERING CYCLONE TRACK THAT MIGRATES INTO THE WESTERN GULF
OF ALASKA AND AMPLIFIES THE DOWNSTREAM FLOW AND UPPER-LEVEL RIDGE
ACROSS WESTERN NORTH AMERICA.

SOME OF THE DETAILS...
ALASKA MEDIUM RANGE PERIOD WILL BE A TRANSITIONAL ONE --- WITH THE
SERIES OF PACIFIC SYSTEMS MIGRATING EAST-NORTHEASTWARD ACROSS THE
SOUTHERN BERING SEA...NORTHERN GULF...SOUTH COAST AND PANHANDLE.
THEN TOWARDS THE END OF THE FORECAST PERIOD --- AN UPPER-LEVEL
RIDGE OVER WESTERN CANADA GRADUALLY REBUILDS NORTHWESTWARD INTO
THE YUKON AND NORTHEAST ALASKA DURING THE DAY 7-8 PORTION OF THE
FORECAST PERIOD AND STEERS A SOUTHERN BERING SEA SYSTEM EASTWARD
AND `UNDERNEATH` THE RIDGE AXIS.

PART OF THE FORECAST CHALLENGE WILL BE THE SOUTHWARD MIGRATION OF
A POLAR TROUGH AND ASSOCIATED SURFACE LOW --- AND ITS ENCOUNTER
WITH A BERING SEA CYCLONE DAYS 6-8. THIS POLAR CIRCULATION WILL
FIRST ENCOUNTER THE WESTERN PERIPHERY OF THE EXPANDING NORTH
AMERICAN RIDGE---DAYS 4-5...THEN RETROGRADE WESTWARD FOR DAYS 6-7
NORTH OF THE ARCTIC CIRCLE. IN THE DAY 6 FORECAST PERIOD
(TRANSITION) --- THE BERING SEA SYSTEM PASSES TO THE SOUTH AND
EAST OF THE POLAR TROUGH --- AND MIGRATES INLAND ACROSS SOUTHWEST
ALASKA AND SHEARS EASTWARD AND NORTHEASTWARD ALONG THE WESTERN
FLANKS OF THE BUILDING UPPER-LEVEL RIDGE.

VOJTESAK

$$





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