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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1835Z Apr 09, 2015)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 PM EDT THU APR 09 2015

VALID 12Z MON APR 13 2015 - 12Z FRI APR 17 2015

THE 9/00Z ECENS...GEFS ENSEMBLE MEANS DETERMINISTIC ECMWF WERE
UTILIZED TODAY---TO DEPICT THE AMPLIFYING PATTERN ANTICIPATED TO
EMERGE ACROSS THE NORTHEAST PACIFIC. THROUGH DAY 6...THE KEY
FEATURE WILL BE AN INTENSIFYING SURFACE LOW---FORMING THE BASE OF
AN UPPER-LEVEL TROUGH---WHICH IS CURRENTLY ESTABLISHING ITSELF
ALONG 160W.

PRIOR TO DAY 6...UNSTABLE AIR WILL MIGRATE SOUTHEASTWARD FROM THE
SOUTHERN BERING SEA INTO THE NORTHWEST GULF OF ALASKA---ACROSS THE
NORTHEAST PACIFIC AND INTO THE MAINLAND'S PACIFIC NORTHWEST. A
SUB-SYNOPTIC SCALE LOW PRESSURE CENTER FORMING JUST SOUTHEAST OF
THE KENAI PENINSULA---ALONG WITH ORGANIZING UPPER-LEVEL ENERGY OFF
THE EAST ASIAN PENINSULA OF KAMCHATKA---WILL APPARENTLY ATTEMPT TO
CONSOLIDATE ALONG 50N 150W BETWEEN DAYS4-6. THE 9/00Z
DETERMINISTIC ECMWF ARE IN VERY GOOD AGREEMENT WITH THE DEPTH AND
LAT/LONG POSITION OF THE SURFACE LOW AT DAY 6---WITH THE 9/00Z
DETERMINISTIC GFS A TAD FURTHER NORTH WITH THIS FEATURE.

THE RATHER GOOD AGREEMENT AT THE SURFACE FOR DAY 6---COINCIDES
WITH THE UPPER-LEVEL FLOW PATTERN DOWNSTREAM---AND ITS AMPLIFIED
CONFIGURATION ALONG 130W FORM THE MID-LATITUDE EAST PACIFIC OCEAN
NORTHWARD INTO WESTERN CANADA.

THIS UPPER-LEVEL RIDGE ALONG THE WEST COAST COAST OF NORTH
AMERICAN SHOULD TURN THE DEEPENING DAY 6 SURFACE CYCLONE
NORTHEASTWARD---AND MIGRATE IT INTO THE NORTHWEST GULF AND
SOUTHWEST COAST OF ALASKA ON/AROUND DAY 7.

THE 2 MAIN CHALLENGES THIS FORECAST PERIOD WILL BE...

(1) WHAT OCCURS UPSTREAM ALONG 50N BETWEEN THE DATELINE AND 170E
LATITUDE---IN RESPONSE TO THE DOWNSTREAM TROUGH-RIDGE COUPLET AND
THE OUTCOME OF ITS AMPLIFICATION? AND (2) THE MIGRATORY TRACK OF
THE DAY 6-8 SYSTEM---MOVING THROUGH THE ALEUTIANS AND NORTHWEST
GULF OF ALASKA.

PERTAINING TO CHALLENGE (1) WOULD HAVE TO BELIEVE THAT THE
TROUGH-RIDGE COUPLET SHOULD SPREAD SOME BROAD-SCALE MOISTURE AND
PACIFIC AIR NORTHEASTWARD ACROSS THE PANHANDLE AND EASTERN
ALASKA---BUT WEAKEN ALONG THE WESTERN PERIPHERY OF THE UPPER-LEVEL
RIDGE AXIS.

TO WHAT EXTENT THIS MOISTURE CONTINUES TO MIGRATE
NORTHWESTWARD---ACROSS THE CENTRAL AND NORTHWEST PORTIONS OF THE
INTERIOR---AND IN WHAT STATE (WEAK OR MODERATELY-ORGANIZED FORM)
REMAINS UNCLEAR.

PERTAINING TO (2) THAT OUTCOME---WILL HAVE A DIRECT RELATIONSHIP
TO THE SECOND OR 'NEW' CYCLONE TRACK AROUND DAY 6-7---INVOF THE
DATELINE. FOR NOW...USED A 70/30 BLEND OF THE ECENS/GEFS
RESPECTIVELY---TO START THIS CYCLONE ON MORE OF A
EAST-SOUTHEASTWARD BOUND TRACK ALONG THE ALEUTIANS---AND
'UNDERNEATH' THE 'WAKE' OF THE LEAD TROUGH-RIDGE COUPLET.

VOJTESAK