Prognostic Meteorological Discussion
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FXAK02 KWNH 281853
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
152 PM EST SUN DEC 28 2014

VALID 12Z THU JAN 01 2015 - 12Z MON JAN 05 2015

CONTINUED WITH THE 28/00Z ECENS MEAN THROUGH THE MEDIUM RANGE
PERIOD---USING THE 28/00Z DETERMINISTIC ECMWF FOR SOME OF THE
SMALLER SCALE DETAILS UNTIL EARLY DAY 6.

BIGGEST FORECAST CHALLENGES WILL BE TO INCORPORATE SENSIBLE
WEATHER CHANGES/FEATURES ALONG THE PERIPHERY OF A BROAD SURFACE
RIDGE---MAINLY IN THE EASTERN BERING SEA AND ACROSS THE EASTERN
ALEUTIANS. IN THIS REGION...A DEEP UPPER-LEVEL TROUGH ATTEMPTS TO
MIGRATE EASTWARD THROUGH DAY 4-5 BEFORE THE DOWNSTREAM UPPER-LEVEL
RIDGE RETROGRADES WESTWARD ACROSS THE ALASKA INTERIOR. WHAT
TRANSPIRES THEREAFTER---IS MORE OF AN `UNDERCUTTING` AND
SOUTHEASTWARD MIGRATION OF THE ENERGY TRANSFER---FROM THE DATELINE
TO APPROXIMATELY 155W LONGITUDE. THE PRIMARY REASON FOR THE
`UNDERCUTTING` MIGRATION APPEARS TO BE THE EMERGENCE OF ANOTHER
WELL-DEFINED WESTERLY PACIFIC JET AXIS OFF THE COAST OF JAPAN. BY
THE END OF THE MEDIUM RANGE PERIOD...MUCH IF NOT ALL THE SENSIBLE
WEATHER IN THE NORTH PACIFIC OCEAN SHIFTS SOUTH---AND AWAY FROM
THE GULF OF ALASKA---DIRECTED INTO THE US MAINLAND AND SOUTHWEST
COAST OF CANADA.

VOJTESAK



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