ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM EDT SAT MAY 11 2013

VALID 12Z WED MAY 15 2013 - 12Z SUN MAY 19 2013

THE MEDIUM RANGE FORECAST FOR ALASKA WILL BE A
CHALLENGE...ESPECIALLY WESTERN ALASKA WITH A SUCCESSION OF
SHORTWAVES AND MORE-ORGANIZED MID-LEVEL CLOSED CIRCULATIONS
SPAWNING OFF A DEEP VORTEX OF COLD AIR NESTLED NORTH OF THE BERING
STRAIT INVOF 72N 170W. A BLEND OF THE 11/00Z EC ENSEMBLE MEANS AND
THE 11/00Z GEFS HANDLES THE LARGE SCALE FLOW AND UPCOMING VORTEX
OF COLD AIR EXPECTED TO SETTLE IN ACROSS THE ARCTIC OCEAN.

THROUGH DAY 6...THE GFS/ECMWF AND CANADIAN ALL HAVE A DECENT
HANDLE ON A PACIFIC SYSTEM MOVING THROUGH SOUTHERN END OF THE
UPPER-LEVEL TROUGH BASE INVOF 50N 175W...AND TRACKING THIS SYSTEM
(A SUB 998 MB LOW) INTO THE WESTERN GULF OF ALASKA ON DAY 6.

THE CHALLENGE WILL BE IN THE BERING SEA WHERE THE BULK OF THE
UPPER-LEVEL COLD POOL AND VORTEX WILL CONTINUE TO BE REPLENISHED
AS THE DAY 5-6 SYSTEM PASSES SOUTH OF THE ALEUTIANS. A STRONG
SHORTWAVE DROPS DOWN INTO THE NORTH BERING SEA NEAR THE DATELINE
AND ENHANCES/REINFORCES THE MODIFIED ARCTIC BOUNDARY AND DEVELOPS
A 'WESTERN' SURFACE FRONT WHICH RACES EAST-SOUTHEASTWARD ACROSS
MUCH OF WESTERN ALASKA. THE 11/00Z CANADIAN/ECMWF/GFS TAKE
DIFFERENT APPROACHES TO REINFORCEMENT OF THIS 'WESTERN' FRONT FOR
DAY 6 THROUGH DAY 8. LIKEWISE...THEY DIFFER IN THE AMOUNT OF
PHASING THAT OCCURS ALONG 165W. THE 11/00Z DETERMINISTIC CYCLE
OFFERED TOO MUCH SPREAD TO BE RELIED UPON AND THE 11/12Z
DETERMINISTIC OFFERED A GOOD COMPROMISE FOR THE SMALLER-SCALE
DETAILS EMBEDDED WITHIN THE LARGE-SCALE UPPER-LEVEL TROUGH AXIS.

VOJTESAK