Prognostic Meteorological Discussion
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FXAK02 KWNH 311909
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
308 PM EDT FRI JUL 31 2015

VALID 12Z TUE AUG 04 2015 - 12Z SAT AUG 08 2015

ALASKA FORECAST DISAGREEMENT OCCURS IN 2 AREAS:  THE FIRST
REVOLVES AROUND HOW ENERGY SOUTH OF THE ALEUTIANS CONSOLIDATES AND
EITHER MEANDERS IN PLACE OR SLIDES EAST INTO THE GULF.   THE 12Z
GFS TUE-WED 04-05 AUG MADE A LARGE CHANGE FROM ITS 06Z RUN WITH
LOW PRESSURE MOVING A DAY FASTER THAN THE PRIOR RUN ACROSS THE
GULF OF AK.  WITH LOW CONFIDENCE IN THE LARGE RUN TO RUN CHANGE IN
THE GFS...THE 12Z GFS RUN WAS NOT USED IN THE FORECAST.

THE ECMWF/ECENS MEAN REPRESENTS BETTER CONTINUITY AND WAS USED IN
CONJUNCTION WITH THE 00Z NAEFS AND 06Z GEFS MEAN.

WITH LOW PRESSURE SFC/ALOFT PERSISTING OVER THE BERING...HIGHER
HEIGHTS OVER MAINLAND AK LEADS TO LOW LEVEL AND SURFACE TEMPS
ABOVE NORMAL MUCH OF THE PERIOD ACROSS SOUTH AND CENTRAL AK.

TO THE NORTH... TREND HAS BEEN TOWARD A BIT MORE TROUGHING PUSHING
THROUGH THE NORTH SLOPE... AND THE FRONTAL BOUNDARY IN THE AREA
DRIFTS SLOWLY SOUTH ACROSS NORTHERN AK. SCATTERED SHOWERS AND
STORMS ARE EXPECTED NEAR THE FRONTAL BOUNDARY IN NORTHERN AK.  THE
2ND AREA OF DISAGREEMENT IS IN NORTHERN AK. MANUAL PROGS TRENDED
AWAY FROM THE 12Z GFS BY NEXT THU/FRI 06-07 AUG AS THE GFS WAS AN
OUTLIER IN DEVELOPING STRONG LOW PRESSURE AND MOVING IT ALONG THE
NORTH COAST...BREAKING CONTINUITY AND IN DISAGREEMENT WITH THE
OTHER MODELS/ENSEMBLE MEANS...INCLUDING THE 12Z GEFS MEAN.

PETERSEN

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