Prognostic Meteorological Discussion
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FXAK02 KWNH 281821
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
121 PM EST WED JAN 28 2015

VALID 12Z SUN FEB 01 2015 - 12Z THU FEB 05 2015

AN ARCTIC HIGH DRAPED ACROSS THE NORTHWEST NORTH AMERICAN
CONTINENT RELEASES DOWNSTREAM INTO THE LOWER 48---WITH AN UPPER
TROUGH ORIGINATING IN NORTHEAST SIBERIA---MOVING SLOWLY ACROSS THE
NORTHERN BERING SEA/BERING STRAIT AND NORTH SLOPE OF ALASKA
BETWEEN DAYS 5-7. THE 28/00Z ECENS/GEFS WERE IN GOOD AGREEMENT
WITH THIS SCENARIO AND SHIFT THE `MEAN` UPPER-LEVEL CYCLONE
EAST-SOUTHEASTWARD INTO A QUASI-STATIONARY POSITION AROUND 50N
160W.

WHAT UNCERTAINTY REMAINS---WILL RESULT FROM THE TRAJECTORY OF
INDIVIDUAL SHORTWAVES ENTERING THE BASE OF THE TROUGH AND
MIGRATING NORTHWARD AND NORTHEASTWARD ALONG 145W-155W. THESE
POLEWARD-MOVING SYSTEMS WILL ENCOUNTER A RATHER STABLE DOWNSTREAM
RIDGE---AND TEND TO SHEAR OUT AS THEY MIGRATE INTO THE CENTRAL
GULF OF ALASKA. A PORTION OF THE WAVE---HEADING DOWNSTREAM INTO
THE WEST-CENTRAL PORTION OF THE CONTINENT...AND A SECONDARY
PORTION OF THE WAVE...MIGRATING NORTHWESTWARD INTO THE EASTERN
ALEUTIANS/NORTHWEST GULF.

AT THESE TIME SCALES...VERY DIFFICULT TO TRACK THE FULL
`LIVE-CYCLE` MIGRATION OF INDIVIDUAL SHORTWAVES BEYOND DAY 6---AND
OPTED TO USE THE ENSEMBLE MEAN APPROACH FOR THE WIDENING DISPARITY
BETWEEN GFS/ECMWF DETERMINISTIC SOLUTIONS IN THE CENTRAL PACIFIC.
THESE DISPARITIES EMERGING ALONG THE BASE OF THE LONG WAVE TROUGH
AXIS---BETWEEN 35N-45N INVOF 160W.

VOJTESAK

$$





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