Prognostic Meteorological Discussion
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FXAK02 KWNH 252009
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
409 PM EDT MON JUL 25 2016

VALID 12Z FRI JUL 29 2016 - 12Z TUE AUG 02 2016

...HEAVY RAIN THREAT ACROSS SOUTHERN/SOUTHEASTERN AK EARLY
ON...THEN SHIFTING BACK INTO WESTERN/INTERIOR SECTIONS OF AK...


...GUIDANCE ASSESSMENT AND WEATHER HIGHLIGHTS/THREATS...

SPLIT FLOW WILL DOMINATE THE SYNOPTIC PATTERN AS MULTIPLE FEATURES
MIGRATE FROM THE WESTERN ALEUTIANS INTO THE GULF OF AK. THE FIRST
OF THESE SYSTEMS IS FORECAST TO BE CROSSING THE NORTHEAST PACIFIC
ON FRIDAY WITH MODELS VARIABLE IN PLACEMENT. RECENT RUNS OF THE
GFS HAVE BEEN QUICKER WITH THE ONLY NOTABLE SUPPORT FROM THE 00Z
UKMET. THIS MORE PROGRESSIVE GROUP IS AHEAD OF THE BETTER
CLUSTERED ENSEMBLE MEANS WHICH SUGGESTS LEANING AWAY FROM THE GFS.
GIVEN THE 00Z ECMWF SOLUTION SOMEWHAT MIRRORS THE ENSEMBLE
MEANS...WILL FAVOR A COMBINATION OF THE 00Z ECMWF AND 00Z ECMWF
ENSEMBLE/06Z GEFS MEANS EARLY ON. AS THIS UPPER TROUGH ADVANCES
TOWARD WESTERN CANADA...ADDITIONAL UNCERTAINTY LOOMS UPSTREAM AS A
SERIES OF ADDITIONAL SHORTWAVES SWING THROUGH THE BERING SEA AND
ADJACENT LOCATIONS. THIS INCLUDES ONE SYSTEM WHICH MAY PEEL OFF
AND RETROGRADE WESTWARD DURING THE SUNDAY/MONDAY TIME FRAME.
ADDITIONALLY...THE GUIDANCE VARY IN HOW TO HANDLE THE MEAN UPPER
TROUGH ANCHORING THE NORTH POLE DOWN INTO CENTRAL AK. GIVEN THE
MYRIAD OF DIFFERENCES AND THE COMPLEX FLOW REGIME AT HAND...AN
ENSEMBLE BASED PROCESS APPEARED TO BE THE WAY TO GO FROM DAY 5
ONWARD UTILIZING APPROXIMATELY 3/4 00Z ECMWF ENSEMBLE MEAN WITH
THE REMAINDER GIVEN TO THE 06Z GEFS MEAN.

THE PATTERN IN PLACE WILL FAVOR HEAVY RAINFALL IN SECTIONS OF AK.
FIRST...THE UPPER TROUGH MOVING THROUGH THE GULF OF AK WILL
SUPPORT AN INCREASE IN LOW-LEVEL SOUTHWESTERLY ONSHORE FLOW ACROSS
SOUTHERN/SOUTHEASTERN AK. THIS SHOULD LEAD TO ENHANCED RAINFALL
AMOUNTS ACROSS THE COASTAL LOCALES OF THE REGION. ELSEWHERE...A
FRONTAL ZONE DROPPING SOUTHWARD ACROSS INTERIOR AK WILL HELP SLIDE
A BROAD BAND OF RAINFALL FROM NORTH TO SOUTH OVER THE STATE. LOCAL
OROGRAPHICS MAY LEAD TO MESOSCALE ENHANCEMENTS ACROSS THESE
FAVORED LOCATIONS.


RUBIN-OSTER

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