Prognostic Meteorological Discussion
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364
FXAK02 KWNH 261916
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
315 PM EDT MON JUN 26 2017

VALID 12Z FRI JUN 30 2017 - 12Z TUE JUL 04 2017

THE AK FCST FOR DAYS 4-8 SHOWS DECENT CONTINUITY/CONSENSUS FOR THE
LARGE SCALE PATTERN EVOLUTION
WITH A HIGH AMPLITUDE BERING SEA TROUGH PERSISTING AND A DEEP
LAYER RIDGE DEVELOPING OVER INTERIOR AK WITH A PERSISTING
WEST-EAST STATIONARY FRONT/TROUGH OVER INTERIOR AK. AN UPPER LEVEL
TROUGH AND SURFACE REFLECTION DRIFTS SLOWLY EAST ACROSS THE GULF
OF AK TO COASTAL AREAS IN THE PANHANDLE AND AREAS FURTHER SOUTH.

TODAY`S BLEND CONSISTED OF THE 12Z GFS/00Z ECMWF COMBINED WITH THE
06Z GEFS MEAN AND 00Z ECMWF ENSEMBLE MEAN INTO THIS WEEKEND. MORE
WEIGHTING WAS GIVEN TO THE ENSEMBLE MEANS EARLY NEXT WEEK DUE TO
GROWING UNCERTAINTY.

CONTINUE TO EXPECT HGT FALLS TO PROCEED INTO THE NERN PAC/GULF OF
ALASKA WITH THE EWD PROGRESSION OF AN UPPER TROUGH FROM THE
ALEUTIANS.  THIS SHOULD LEAD TO A SLOWLY MOVING CLOSED OVER THE
GULF OK AK THAT GRADUALLY
WEAKENS AND SHEARS EAST EARLY NEXT WEEK. THE 12Z GFS ADJUSTED TO
BE CLOSER TO THE 00Z ECMWF AND CANADIAN GLOBAL MODELS WITH THE LOW
EVOLUTION...SO A BLENDED SOLUTION WAS USED.

MEANWHILE WRN CANADA MEAN RIDGING RETROGRADES AND BUILDS WEST
ACROSS THE MAINLAND.  THERE WILL BE AN ENHANCED CHANCE OF SHOWERS
NEAR THE SFC FRONT IN NORTHERN AK BUT A DECLINE BOTH SOUTH INTO
CENTRAL AK AND NORTH NEAR THE NORTH COAST.

UPSTREAM THERE IS STILL FAIR AGREEMENT ON THE DEVELOPMENT OF A
MEAN TROUGH FROM SIBERIA SWD THROUGH THE EXTREME WRN BERING SEA
AND WRN PAC.  HOWEVER BY MID-LATE PERIOD THERE IS WIDE
MODEL/ENSEMBLE SPREAD AND POOR RUN-RUN MODEL CONTINUITY FOR
DETAILS WITHIN AND AHEAD OF THE MEAN TROUGH ACROSS MUCH OF THE
BERING SEA AS THE ECMWF AND GFS HAVE MADE SIGNIFICANT RUN TO RUN
CHANGES REGARDING WHERE EMBEDDED WAVES DEVELOP AND TRACK.  FOR NOW
IT IS DIFFICULT TO HAVE ANY CONFIDENCE IN A PARTICULAR MODEL
SOLN/RUN SO PREFER TO LEAN MORE TO THE ENSEMBLE MEANS UNTIL BETTER
AGREEMENT DEVELOPS.

PETERSEN

$$





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