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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 1750Z May 23, 2017)
 
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Abbreviations and acronyms used in this product
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
150 PM EDT TUE MAY 23 2017

VALID 12Z SAT MAY 27 2017 - 12Z WED MAY 31 2017

MODELS AND ENSEMBLES CONTINUE TO CHANGE THEIR TUNE IN THE MEDIUM
RANGE THOUGH AT LEAST THEY ARE SINGING THE SAME SONG. SYNOPTIC
PATTERN FAVORS TROUGHING ALONG 160-170W WITH RETROGRADING RIDGING
FROM NW CANADA. BIGGEST QUESTION IS HOW TO HANDLE THE FLOW THROUGH
THE NORTH PACIFIC, WHICH WILL AFFECT THE ALEUTIANS INTO SOUTH
CENTRAL AREAS NEXT WEEK. THE ECMWF AND ITS ENSEMBLES DIFFER ON
WHICH SHORTWAVE AND SFC FRONT TO EMPHASIZE COMPARED TO THE
GFS/CANADIAN AND THEIR ENSEMBLES. THOUGH THE ECMWF TYPICALLY
HANDLES AMPLIFIED FLOW BETTER THAN THE GFS/GEFS, IT USUALLY HAS
SOME SUPPORT FROM THE CANADIAN (WHICH LIKES TO BE AMPLIFIED AS
WELL). HOWEVER, THE FORECAST BUST FROM LAST WEEK OF ALL BUT THE
ECMWF JUST MEANS THERE IS LESS CONFIDENCE IN THE FORECAST DETAILS.

GIVEN THE LARGE SHIFT IN THE ECMWF ENSEMBLES, OPTED TO MAKE A
PARTIAL SHIFT VIA A BLEND BETWEEN THE 00Z GEFS AND THE ECMWF
ENSEMBLES FOR THE FIRST PART OF THE PERIOD BEFORE TRANSITIONING TO
THE 06Z GEFS MEAN. THIS KEPT TWO SEPARATE SYSTEMS (LIKE
CONTINUITY) UNTIL NEXT WEDNESDAY SINCE IT SEEMS THAT THE ECMWF
ENSEMBLES WERE BLURRING THE TWO TOGETHER INTO AN ELONGATED LOW
JUST SOUTH OF THE ALEUTIANS. THE ECMWF ITSELF WAS RATHER AN
AMPLIFIED VERSION OF ITS MEAN BUT IT ONLY DEVELOPED THE LEAD LOW
(OPPOSITE THE 12Z GFS).

TEMPERATURES ACROSS THE MAINLAND WILL TREND FROM BELOW AVERAGE TO
NEAR AVERAGE THROUGH THE PERIOD, BUT MOSTLY ABOVE AVERAGE ON THE
NORTH SLOPE. PRECIPITATION AMOUNTS ARE UNCERTAIN, DEPENDING ON HOW
CLOSE AND DEVELOPED THE SURFACE LOW (OR LOWS) BECOME SOUTH OF THE
ALEUTIANS. HIGHEST POPS WERE ACROSS THE EASTERN ALEUTIANS THROUGH
SOUTH CENTRAL.


FRACASSO