Prognostic Meteorological Discussion
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FXAK02 KWNH 211847
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 PM EDT FRI JUL 21 2017

VALID 12Z TUE JUL 25 2017 - 12Z SAT JUL 29 2017

THE LARGE SCALE FLOW PATTERN ACROSS ALASKA CONTINUES TO SHOW A
RELATIVELY HIGH DEGREE OF PREDICTABILITY FOR DAYS 4-8. A
PERSISTENT UPPER RIDGE OVER THE NORTH PACIFIC WILL BUILD EAST INTO
THE ALEUTIANS BY THE MIDDLE TO END OF NEXT WEEK. MEANWHILE, A
TROUGH WILL BECOME REESTABLISHED ACROSS THE GULF OF ALASKA AFTER
AN UPPER LOW INITIALLY IN PLACE ON DAYS 4-5 MOVES EAST INTO THE
COAST. FARTHER NORTH, AN AREA OF NEGATIVE HEIGHT ANOMALIES WILL
PERSIST ACROSS THE ARCTIC OCEAN. THE COMBINATION OF THESE LARGE
SCALE FEATURES WILL KEEP MUCH OF MAINLAND ALASKA IN FAIRLY
PROGRESSIVE WESTERLY FLOW AT THE MID/UPPER LEVELS, WITH A SERIES
OF SHORTWAVES TRAVERSING THE STATE THROUGH THE FORECAST PERIOD. A
SHORTWAVE CROSSING THE STATE ON DAY 4 (TUE) WILL INFLUENCE THE
DEVELOPMENT OF THE TROUGH/UPPER LOW IN THE GULF OF ALASKA BY DAY 6
(THU). MODELS SHOW SOME TIMING DIFFERENCES ON THIS SHORTWAVE, WITH
THE GFS A BIT FASTER THAN THE ECMWF AND GEM GLOBAL. TIMING AND
AMPLITUDE DIFFERENCES TRANSLATE INTO DIFFERENCES IN THE EVENTUAL
UPPER LOW ACROSS THE GULF, WITH A RANGE OF SOLUTIONS EVIDENT BY
LATE NEXT WEEK WITH RESPECT TO THE EVENTUAL PLACEMENT AND DEPTH OF
THE UPPER LOW. ALSO BY LATE NEXT WEEK, A COUPLE ADDITIONAL
SHORTWAVES ARE FORECAST BY ALL GUIDANCE TO MOVE FROM NORTHEASTERN
RUSSIA INTO THE BERING STRAIT AND WESTERN AK. THE GFS AND ECMWF
ARE RELATIVELY SIMILAR IN THEIR TIMING/INTENSITY WITH RESPECT TO
THIS SYSTEM, WHICH SHOULD SUPPORT AT LEAST SOME USE OF THESE
DETERMINISTIC SOLUTIONS IN THE FORECAST THROUGH DAY 8.


RYAN

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