Prognostic Meteorological Discussion
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133
FXAK02 KWNH 132011
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
311 PM EST WED DEC 13 2017

VALID 12Z SUN DEC 17 2017 - 12Z THU DEC 21 2017

...STRONG SYSTEM IN THE BERING SEA NEXT WEEK...

ENSEMBLE MEANS CONTINUE TO SHOW THE PATTERN CHANGE TOWARD AN UPPER
LOW IN THE FAR WESTERN BERING SEA OR OVER KAMCHATKA WITH BUILDING
HEIGHTS OVER THE MAINLAND AND EVENTUALLY THE PANHANDLE. THE FLOW
IS FORCED BY A STRONG JET COMING OFF THE ASIAN CONTINENT WITH
SPLIT FLOW AROUND AND EAST OF THE DATELINE. THIS YIELDS AN UPPER
LOW TO THE NORTH AND NORTHWEST OF HAWAI`I AND A STORM TRACK
NORTHWEST OF THE MID-LATITUDES OF THE N PAC NORTHEASTWARD THROUGH
THE BERING SEA.

THE FIRST FEW DAYS OF THE PERIOD (SUN-TUE) SHOW DECENT CLUSTERING
OF THE DETERMINISTIC SOLUTIONS SO THAT A MULTI-MODEL BLEND SERVED
AS A GOOD STARTING POINT (12Z/06Z GFS AND 00Z
ECMWF/CANADIAN/UKMET). THIS GAVE A RESPECTABLE LOW CENTER OF ABOUT
955MB IN THE FAR WESTERN BERING SEA (MODEL PMSLS WERE ABOUT
945-955MB). WITH BUILDING RIDGING TO THE EAST PARENT LOW SHOULD
FILL OVER NORTHEASTERN RUSSIA AND THE COLD FRONT MAY JUST
DISSIPATE OVER WESTERN ALASKA AS ANOTHER WAVE TRIES TO RIDE ALONG
THE FRONT. BY THEN (NEXT WED) THE MODELS DIVERGE ON WHAT SFC WAVE
AND WHAT SUBSEQUENT SYSTEM WEST OF THE ALEUTIANS MAY DEVELOP.
TRENDED TOWARD 50/50 ENSEMBLE MEAN WEIGHTING TO SMOOTH OUT THE
INCONSISTENCIES. THIS KEPT GOOD CONTINUITY BY NEXT WED INTO THU
WITH ANOTHER SYSTEM SLIDING UNDERNEATH THE OLD PARENT LOW OF THE
LEAD BERING SYSTEM.

STRONG WINDS (50KTS SUSTAINED AND GUSTS OVER 70KTS) ARE LIKELY FOR
THE UNFROZEN OPEN BERING AND ELEVATED ALEUTIANS AS THE COLD FRONT
PUSHES EASTWARD MONDAY. MODEST TO LOCALLY HEAVY RAIN/SNOW ARE
POSSIBLE FROM THE ISLAND CHAIN INTO WESTERN ALASKA. THIS SHOULD
BRING MILDER AIR AT LEAST ALOFT INTO MOST OF THE INTERIOR WEST OF
ABOUT 155W.


FRACASSO


$$





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