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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 1910Z Sep 30, 2014)
 
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Abbreviations and acronyms used in this product
 
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ALASKA EXTENDED FORECAST DISCUSSION...CORRECTED PARAGRAPH 3
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 PM EDT TUE SEP 30 2014

VALID 12Z SAT OCT 04 2014 - 12Z WED OCT 08 2014

SYNOPTIC PATTERN ACROSS HIGH LATITUDES DURING THE MEDIUM RANGE
PERIOD SUGGESTS TROUGHING ACROSS NORTHEAST SIBERIA WILL PROGRESS
SLOWLY EASTWARD THROUGH TIME---ANCHORING IN THE SOUTHERN BERING
SEA AROUND MID PERIOD. TO GET TO THIS DAY 5-6 MID-PERIOD TIME
FRAME...MUCH HAS YET TO SETTLE OUT DOWNSTREAM.

THE SHORT-TERM CONCERNS WITH 'KAMMURI' DO INFLUENCE THE GULF OF
ALASKA...DICTATE THE OUTCOME OF THE LEAD UPPER-LEVEL TROUGH
PROGRESSION...AND EVENTUAL EAST-NORTHEASTWARD MIGRATION OF A
SHORTWAVE UPPER-LEVEL RIDGE CURRENTLY INVOF 140W---INTO THE YUKON
AND BC. THE ECMWF/GFS GENERALLY SET THE TONE HEADING INTO DAY
4...AS THE SURFACE WAVE ENERGY MIGRATING THROUGH THE SOUTHEAST
INTERIOR AND PANHANDLE BEGIN TO NUDGE THE SHORTWAVE RIDGE INTO
CANADA. BUT CONFIDENCE IS LOW IN THAT 'PERFECT PROG' SCENARIO FOR
THE FLOW PATTERN TO TRANSITION ACROSS THE GULF OF ALASKA.

A BUSY AND ACTIVE TROPICAL AND SUBTROPICAL WESTERN PACIFIC THIS
MEDIUM RANGE PERIOD WILL CONTINUE TO THROW RUN-TO-RUN UNCERTAINTY
INTO THE MID-LATITUDE WESTERLY FLOW PATTERN ALOFT BEYOND DAY
5---ESPECIALLY WITH THE POTENTIAL FOR MID-LATITUDE CYCLOGENESIS
INVOF THE DATELINE AND 45N-50N LATITUDE. THE KAMCHATKA REGION AND
SOUTHERN BERING SEA SHOULD BE RATHER ACTIVE...WITH AN APPROACHING
UPPER-LEVEL COLD CORE AND ASSOCIATED SURFACE LOW IN A POSITION
FAVORABLE FOR ENTRAINMENT OF REMNANT 'PHANFONE' MOISTURE AND
ENERGY. THIS ADDS A CONSIDERABLE AMOUNT OF UNCERTAINTY IN THE
MEDIUM RANGE. NOT ONLY WITH THE DEPTH...STRUCTURE AND LOCATION OF
THE PARENT CYCLONE IN THE SOUTHERN BERING SEA...BUT ALSO WITH THE
REGION OF SECONDARY CYCLOGENESIS DOWNSTREAM ALONG 50N BETWEEN THE
DATELINE...165W LONGITUDE AND EVENTUALLY...THE GULF OF ALASKA
PROPER.

ALTHOUGH THE 30/00Z ECENS MEAN AND 30/06Z GEFS GENERALLY AGREE
WHERE THE PARENT UPPER-LEVEL CYCLONIC CIRCULATION WILL SETTLE IN
THE SOUTHERN BERING SEA...CYCLOGENESIS ALONG THE BASE OF THE
UPPER-LEVEL TROUGH...IS HANDLED VERY DIFFERENTLY BETWEEN THE
ECMWF...GFS AND CANADIAN AROUND THE 6/00Z TIME FRAME.

FOR NOW...BLENDED THE ENSEMBLE MEANS MENTIONED ABOVE FOR DAYS 4-8.
SUSPECT THE FORECAST FOR EARLY NEXT WEEK WILL CHANGE...ALTERED BY
THE FLOW TRANSITIONING ACROSS THE GULF OF ALASKA IN THE SHORT
TERM. GIVEN THE VAST MODEL DIFFERENCES WEST OF THE DATELINE IN THE
MID-LATITUDE PACIFIC AND ALONG THE WESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE IN THE MEDIUM RANGE---POSSIBLE PHASING
CONCERNS---OFFER A MUCH LOWER THAN NORMAL CONFIDENCE LEVEL
FORECAST.

VOJTESAK