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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1916Z Aug 31, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
316 PM EDT SUN AUG 31 2014

VALID 12Z THU SEP 04 2014 - 12Z MON SEP 08 2014

THE ALASKAN FLOW PATTERN FEATURES A MAJOR ARCTIC VORTEX CENTERED
JUST NORTH THEN INCREASINGLY NORTHEAST OF THE NORTH SLOPE FOR MUCH
OF THIS WEEK. THIS ALLOWS A PERIOD OF MID-UPPER LEVEL TROUGHING
FROM THE ARCTIC OCEAN THROUGH THE INTERIOR. EXPECT BELOW NORMAL
TEMPS AS 500/700 MB HEIGHT ANOMALIES REACH 2-3 STANDARD DEVIATIONS
BELOW NORMAL NORTH OF THE ARCTIC CIRCLE. THE MAIN CLOSED VORTEX
DOES THOUGH MOVE STEADILY EASTWARD LATER WEEK...LOSING INFLUENCE
WITH TIME OVER ALASKAN WEATHER. THE PATTERN AND ADDITIONAL TROUGH
ENERGY DEVELOPMENT AND APPROACH SEWD FROM THE BERING SEA ALLOWS
RELATIVELY MODEST LEAD IMPULSE AND SURFACE SYSTEM DEVELOPMENT AND
PCPN/WEATHER FOCUS UNDERNEATH OVER THE ALASKAN SRN/SERN TIER AND
NRN GULF OF AK OVERTOP A NE PACIFIC MID-UPPER LEVEL RIDGE. WPC AND
GUIDANCE OFFER A SLIGHTLY MORE PROGRESSIVE SYSTEM TRANSLATION
COMPARED TO YESTERDAYS PROGS THAT IN RETROSPECT SEEMED TOO SLOW
GIVEN CHANNELED FLOW PATTERN.  

MEANWHILE...UPSTREAM DEVELOPMENT ACROSS THE MID-UPPER PACIFIC
LATITUDES OF A AMPLIFIED MEAN MID-UPPER LEVEL TROUGH JUST SOUTH OF
THE ALEUTIANS SHOULD FAVOR CYCLOGENESIS/FRONTOGENESIS THAT SEEMS
MOST LIKELY TO ORGANIZE AND WORK TOWARD THE ALEUTIANS AND SW
ALASKA LATE WEEK INTO DAYS 7/8 AROUND THE WRN PERIPHERY OF THE
AFOREMENTIONED NERN PACIFIC RIDGE.

MODELS AND ENSEMBLES OFFER SOMEWHAT MORE COMPATABLE GUIDANCE THAN
IN RECENT DAYS THIS WEEK. HOWEVER...MORE SIGNIFICANT DIFFERENCE
BETWEEN ENSEMBLE MEANS AND THEIR RESPECTIVE DETERMINISTIC MODEL
RUNS STILL LENDS PAUSE AT LONGER TIME FRAMES...EVEN WHEN THE GFS
AND ECMWF ARE IN DECENT AGREEMENT AS OVER THE ARCTIC WITH ANOTHER
DEEP LOW OFF THE NORTH SLOPE DAYS 7/8. WPC PROGS LIMIT DEVELOPENT
THERE FOR NOW GIVEN UNCERTAINTY. THE WPC ALASKAN MEDIUM RANGE
PRODUCT SUITE REMAINS PRIMARILY DERIVED FROM AN ENSEMBLE MEAN
FORECAST APPROACH. THE 00 UTC ECMWF ENSEMBLE MEAN WAS MAINLY USED
AS IT TODAY SEEMS TO BEST MAINTAIN WPC PATTERN CONTINUITY.

SCHICHTEL