Prognostic Meteorological Discussion
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FXAK02 KWNH 271830
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
229 PM EDT THU AUG 27 2015

VALID 12Z MON AUG 31 2015 - 12Z FRI SEP 04 2015

THE PREVIOUS TWO ECENS RUNS AND THE 27/00Z GEFS WERE IN RATHER
GOOD AGREEMENT WITH THE MID-LEVEL FLOW PATTERN AND LOW-LEVEL
NORTHERN STREAM COLD ADVECTION SEQUENCE ---FOR DAYS 4-5.

THE PLACEHOLDER---FOR MUCH OF THE MEDIUM RANGE PERIOD HAS BEEN AND
SHOULD CONTINUE TO BE--- THE CIRCULATION FORMALLY KNOWN AS
`ATSANI`. ITS LOCATION NEAR 40N 170E SERVES TO CYCLE SUBTROPICAL
MOISTURE NORTHWARD FROM NORTHWEST OF HAWAI`I DOWNSTREAM INTO THE
THE NORTHERN STREAM FLOW PATTERN. THE CURRENT FORECASTS DO
OCCASIONALLY RECYCLE THIS MOISTURE AND ENERGY---AND IN THE
PROCESS--ALLOW SOME SHORTWAVE RIDGING TO MIGRATE THROUGH THE
DOWNSTREAM CONFLUENCE AND KEEP SHORTWAVE ENERGY ON `MORE OR LESS`
A SEQUENTIAL MIGRATION PATH FROM THE SOUTHERN YUKON DELTA TO THE
OLYMPIC PENINSULA OF WASHINGTON STATE.

ESPECIALLY BEYOND DAY 6---THE CHALLENGE IS THE PLACEMENT AND
TIMING OF THE SUBTROPICAL ENTITIES INTO THE DOWNSTREAM FLOW.
SOLUTIONS WITH SLOWER-MOVING IMPULSES TEND TO PROVIDE MORE
AMPLIFICATION/BLOCKING AT HIGHER LATITUDES (MAINLY ALONG 50N).
FASTER-MOVING SOLUTIONS KEEP THE FLOW MUCH MORE ZONAL ALONG 50N.
GIVEN WHAT IMPACTS THESE SUBTROPICAL IMPULSES HAVE HAD ON THE
PREVIOUS 7-10 DAYS WORTH OF FORECASTS ALONG THE DATELINE---WILL
CONTINUE WITH THE ECENS MEANS AS `PLACEHOLDER` FOR DRIVING THE
DOWNSTREAM SENSIBLE WEATHER PATTERN...WHICH WILL EVENTUALLY ALLOW
THE `NEW` CIRCULATION TO DRIFT SLOWLY ACROSS THE ALEUTIANS AND
SPREAD INTO THE SOUTHERN BERING BY PERIOD`S END.




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