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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 1826Z Apr 26, 2015)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
226 PM EDT SUN APR 26 2015

VALID 12Z THU APR 30 2015 - 12Z MON MAY 04 2015

AFTER A PERIOD OF LARGE ENSEMBLE SPREAD... IT APPEARS THAT THE
GUIDANCE IS SHOWING SIGNS OF COMING TOGETHER TOWARD A MAINTAINING
AN UPPER LOW IN THE BERING SEA. DOWNSTREAM OVER THE GULF... THE
PATTERN IS MUCH MORE CHANGEABLE WHICH LEAVES ROOM FOR MORE ERROR
IN SYSTEM EVOLUTION. TO THE NORTH... WEAK RIDGING IS EXPECTED TO
LINGER JUST NW OF THE NORTH SLOPE.

MODELS/ENSEMBLES HAVE LARGELY TRENDED A BIT SLOWER... ABOUT 12-18
HRS... FROM THU/D4 ONWARD WITH THE PATTERN. ECMWF DROPPED ITS IDEA
OF A QUICKER/PHASED AND MORE NORTHERN-STREAM DOMINATED SYSTEM
ALONG THE ALEUTIANS THU-FRI IN FAVOR OF A SLOWER AND
SOUTHERN-ORIGIN LOW THAT THE MODELS BASICALLY ALL SHOW. OUT OF
SYNC GFS RUN FROM THE 25TH TRENDED TOWARD THE ECMWF/CONSENSUS FROM
YESTERDAY BUT STILL SHOWS A MORE DEFINED NORTHERN LOW ON THU/D4
THAT IS NOT OUT OF THE QUESTION... BUT SHOULD SHEAR OUT BY FRI/D5
AS THE OTHER SYSTEM DEEPENS. THAT SHOULD TRACK NORTHEASTWARD
TOWARD AND INTO THE GULF NEXT WEEKEND THOUGH THE QUASI-SPLIT FLOW
MAY TUG IT MORE NORTHWARD OR EASTWARD DEPENDING ON DETAILS. FOR
NOW... LET THE ENSEMBLES LEAD THE WAY -- 06Z GEFS AND 00Z ECENS
MEAN -- TAKING THE LOW NORTHEASTWARD AND DISSIPATING. 12Z GFS
ACTUALLY SHOWS A BETTER PROGRESSION THAN THE ECMWF HERE BUT GIVEN
THE CHANGEABILITY OF RECENT MODEL RUNS CANNOT RULE ANYTHING OUT.
FOR NEXT SUN-MON... ENSEMBLES AND MODELS SHOW GOOD AGREEMENT FOR
THAT TIME RANGE BRINGING IN ANOTHER UPPER/SFC LOW INTO THE BERING
SEA.


FRACASSO