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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1827Z Apr 13, 2015)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
227 PM EDT MON APR 13 2015

VALID 12Z FRI APR 17 2015 - 12Z TUE APR 21 2015

THE 13/00Z MODEL GUIDANCE WAS PRETTY MUCH LOCKED-IN WITH THE
UPPER-LEVEL FLOW PATTERN AND HIGH-AMPLITUDE UPPER-LEVEL RIDGE
CONFIGURATION ACROSS THE WEST COAST OF CANADA---AND THE PANHANDLE.

AN EXPANSIVE DAY 5-6-7 CYCLONE CONTINUES TO BE THE PRIMARY
SENSIBLE WEATHER FEATURE IN THE ALASKA MEDIUM RANGE PERIOD. THIS
DEEP AND HIGHLY-AMPLIFIED SYSTEM WILL GRADUALLY WORK ITS LOW-LEVEL
COLD FRONT WEST-TO-EAST ACROSS THE GULF OF ALASKA DURING THE
PERIOD. ITS DECAYING OCCLUSION AND DEFORMATION CLOUD SHIELD  IS
EXPECTED TO WORK NORTHWARD INTO THE NORTH SLOPE REGION OF
ALASKA---DAYS 7-8.

THE CURRENT WPC SURFACE AND 500MB GRAPHICS HAVE DEVIATED VERY
LITTLE FROM THEIR PREVIOUS PROGS AND REMAIN TIED CLOSELY TO THE
ECENS/ECMWF AND 13/00Z VERSION OF THE NAEFS. THE ONE PORTION OF
THE FORECAST GRAPHIC SEQUENCE THAT HAS BEEN ALTERED---A DAY 7-8
DRY SLOT AND TROUGH AXIS---INVOF 145W. THE CANADIAN AND ECMWF
DETERMINISTIC GUIDANCE DO DIFFER HERE---WITH RESPECT TO THE
SHORTWAVE'S TIMING---AND TRAJECTORY. FOR NOW...WILL CARRY THIS
WAVE AS A SOUTHWEST-TO-NORTHEAST MOVING TROUGH...MIGRATING
UNDERNEATH THE DECAYING BROAD OCCLUSION. ALTHOUGH IT APPEARS TO BE
A PURE COLD-ADVECTION TYPE SHORTWAVE...THIS MAY END UP BEING
SOMEWHAT OF A SMALLER-SCALE FEATURE EMBEDDED ALONG THE BROAD
SYSTEM'S DRY SLOT (AND CONVECTIVE IN NATURE).

VOJTESAK