Prognostic Meteorological Discussion
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FXAK02 KWNH 271856
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION...CORRECTED TYPO PARAGRAPH 2
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 PM EDT MON APR 27 2015

VALID 12Z FRI MAY 01 2015 - 12Z TUE MAY 05 2015

ACROSS THE EASTERN HALF OF THE PACIFIC---AND THE NORTH AMERICAN
CONTINENT---A DISTINCT SPLIT-FLOW PATTERN IS ANTICIPATED TO
EMERGE---WITH THE NORTHERN PORTION OF THE JET-LEVEL SPLIT FLOW
PATTERN TO MAINTAIN A WESTERLY COMPONENT ALONG 50 NORTH
LATITUDE---FROM THE DATELINE TO 130W LONGITUDE. THE PERSISTENCE OF
THE NORTHERN STREAM---ALLOWS FOR A GRADUAL SOUTHEASTWARD SHIFT OF
THE SOUTHERN END OF AN UPPER-LEVEL TROUGH IN THE SOUTHERN BERING
SEA---TO MIGRATE INTO THE WEST CENTRAL GULF OF ALASKA. THE
TRANSITION FROM BERING TO GULF---TAKES PLACE IN THE DAY 5-6 TIME
FRAME...AND `NEW` ENERGY OFF THE COAST OF EAST CENTRAL ASIA
ATTEMPTS TO REINFORCE THE RESIDUAL LONGWAVE TROUGH NEAR THE
DATELINE AND BERING SEA ON DAY 7-8.

TO KEEP THE TRANSITION SIMPLE IN THIS FAST WESTERLY SPLIT-FLOW
PATTERN WILL BE A CHALLENGE---AND THE MODEL GUIDANCE THAT BEST FIT
THE EXPECTATIONS OF THE FORECAST WAS A BLEND OF THE 27/00Z ECENS
AND NAEFS MEANS.

THERE WILL LIKELY NEED TO BE SOME ALTERATIONS (IN THE FUTURE)
CONCERNING THE LOWER LAYERS---PARTICULARLY THE SURFACE WINDS IN
THE DAY5-6 PERIOD---ONCE SOME OF THE MID-LEVEL ENERGY AND
UPPER-LEVEL TROUGH BREAKS INTO THE GULF OF ALASKA. THE CURRENT
DETERMINISTIC FORECAST SOLUTIONS---ECMWF, GFS AND CANADIAN, ALL
SHOW A `TRACK-ABLE` A SURFACE CYCLONE MIGRATION INTO THE WESTERN
GULF---THAT FIT THE ENTIRE ENVELOPE OF BOTH PREFERRED MEANS. BUT
EACH SOLUTION VARIED A TAD TOO MUCH TO BE RELIED UPON FOR `PERFECT
PROG` INSERTION INTO THIS PARTICULAR FORECAST PACKAGE.

VOJTESAK



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