Prognostic Meteorological Discussion
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FXAK02 KWNH 261914
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
311 PM EDT TUE JUL 26 2016

VALID 12Z SAT JUL 30 2016 - 12Z WED AUG 03 2016

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

SPLIT-FLOW PATTERN FEATURES ANOTHER MODERATE ARCTIC SHORTWAVE
MIGRATION ACROSS THE STATE FROM NORTHWEST TO SOUTHEAST --- IN THE
DAY 4-5 TIME FRAME. THIS COOLER AIR SEEPS INTO THE GULF OF ALASKA
AND RE-INVIGORATES A MOIST CYCLONIC FLOW FOR THE COAST AND FRONTAL
PRECIPITATION AND BREEZY CONDITIONS ACROSS THE INTERIOR.

THE CHALLENGE WILL BE WHAT THE FLOW PATTERN LOOKS LIKE ALOFT IN
THE GULF OF ALASKA AND SOUTHERN BERING SEA ONCE THE MID-LEVEL AND
UPPER-LEVEL TROUGH EXITS THE STATE. WHAT HAS BEEN THE PATTERN
ACROSS THE ARCTIC CIRCLE AND NORTHWARD HAS BEEN FOR A COOLER
WESTERLY FLOW FROM NORTHEAST RUSSIA TO PREVAIL...A POLAR CYCLONE
TO LIFT AWAY FROM THE REGION...AND EMBEDDED SHORTWAVES TO BRUSH
ACROSS THE NORTH COAST.

BUT ACROSS THE GULF...THE PATTERN HAS LESS PREDICTABILITY.
ESPECIALLY WITH THE LAT/LONG POSITIONING OF THE CYCLONIC CENTER
ALOFT AS THE `ARCTIC-ORIGINATING` TROUGH AXIS SHEARS OUT OR SPLITS
(GENERALLY SOUTH OF 55N LATITUDE). AS THE TROUGH MIGRATES IN
WNW-TO-ESE FASHION THROUGH THE SOUTHEAST QUARTER OF THE STATE AND
NORTHEAST GULF...SURFACE WAVE DEVELOPMENT HAS "TYPICALLY" BEEN ON
THE `WEAKER` SIDE AND/OR DIRECTED INTO SOUTHERN BC AND WEST
CENTRAL ALBERTA. THE QUESTION IS --- WILL THE CURRENT MEDIUM
FORECAST PATTERN BE THE `PROGRESSIVE` PATTERN ACROSS THE WEST
CENTRAL PORTION OF CANADA? OR WILL A CUTOFF LOW FORM OFF THE
SOUTHWEST COAST OF CANADA.

USING THE 26/00Z ECENS...CANADIAN AND GEFS MEANS SEEMED TO WORK
WELL ACROSS THE ARCTIC PORTION OF THIS SPLIT-FLOW PATTERN...BUT
THE GEFS WAS THE LEAST PROGRESSIVE SOLUTION ALOFT ACROSS THE
SOUTHWEST INTERIOR VERSUS THE ECENS AND CANADIAN ENSEMBLE MEAN
GUIDANCE. WE PREFERRED THE LATTER SOLUTION TODAY ACROSS ALASKA AND
CARRY A DECENT MID-LEVEL WAVE DOWNSTREAM ACROSS THE NORTHEAST
PACIFIC AND INTO THE NORTH AMERICAN CONTINENT.

VOJTESAK

$$





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