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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1920Z Nov 20, 2014)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EST THU NOV 20 2014

VALID 12Z MON NOV 24 2014 - 12Z FRI NOV 28 2014

FOR THIS PARTICULAR MEDIUM RANGE FORECAST PERIOD---MON (24/12Z) TO
FRI (28/12Z)--THE SOUTHERN BERING SEA WILL BE THE AREA FOR RENEWED
CYCLOGENESIS AND IN A GENERAL SENSE---A BROAD CYCLONIC MID-LEVEL
TO UPPER-LEVEL FLOW WILL PREVAIL DURING THIS TIME FRAME.

THE NORTH PACIFIC JET STREAM REMAINS GENERALLY DISPLACED TO THE
SOUTH---CLOSER TO 45 N LATITUDE---FOR MOST OF THE PERIOD---EXCEPT
IN THE DAY 5-6 WINDOW---WHEN A SUBTROPICAL CONNECTION OF MOISTURE
AND MID-LEVEL ENERGY BRIEFLY 'LINKS UP' WITH THE PACIFIC JET AND
IS QUICKLY WHISKED INLAND ACROSS THE WESTERN COAST OF CANADA.
AHEAD OF THIS 'LINK UP' AND SHORTWAVE RIDGE ATTEMPTS TO BUILD
NORTHWARD ALONG 135W LONGITUDE AND EDGE INTO THE SOUTHEAST PORTION
OF THE GULF OF ALASKA.

THERE IS NO MAJOR SHIFT IN FORECAST PHILOSOPHY WITH THE 20/00Z
CYCLE---FOR THE ECENS/GEFS HAVE GENERALLY IDENTIFIED THE KEY
FEATURES AND THEIR PROGRESSION ACROSS THE NORTHEAST PACIFIC. WHAT
LACKS DEFINITION---APPEARED TO BE---THE EXACT TIMING OF
SUBTROPICAL ENERGY NORTHEASTWARD...AND WHICH NORTHERN PACIFIC
JET-DRIVEN SHORTWAVE HAS THE ABILITY TO TAKE THE SUBTROPICAL
MOISTURE PLUME INTO THE WEST COAST OF NORTH AMERICA ALONG THE
UPWIND (WESTERN) SIDE OF THE UPPER-LEVEL RIDGE. THE 20/00Z
DETERMINISTIC GUIDANCE MAINTAINS AN UNUSUALLY LARGE SPREAD AND
VARIETY OF SOLUTIONS WITH THE ORGANIZATION OF MOISTURE/ENERGY
EMERGING JUST NORTH OF HAWAI'I BETWEEN 24/12Z AND 26/00Z.

THE SUBTROPICAL MOISTURE INTRUSION (PLUME) REMAINS SEPARATED FROM
(OR DETACHED) FROM THE MID-LATITUDE WESTERLIES AND NO PHASING IS
ANTICIPATED INVOF THE GULF OF ALASKA. IF ANYTHING...A STEADY
'STREAMER' OF MOISTURE AND POSITIVE-TILT TROUGH BRUSHES THE
SOUTHERN HALF OF THE PANHANDLE BRIEFLY...BEFORE PROGRESSING
EASTWARD INTO SOUTHERN BC...THE WASHINGTON COAST AND SOUTHWARD
TO---VERY NEAR 42N 125W---LATE IN THIS FORECAST PERIOD.

WITHOUT EXCEPTION...THE DETERMINISTIC RUNS DO GENERATE A SERIES OF
WEAK SURFACE REFLECTIONS BENEATH THE SUBTROPICAL JET...BUT THESE
INDIVIDUAL WAVES APPEAR TO DISINTEGRATE IN WHAT BECOMES A
HIGHLY-SHEARED MID-LATITUDE WESTERLY JET PATTERN. EVEN THE CLOSED
LOW SOLUTIONS NEVER TRULY MAINTAIN SUFFICIENT LOW-LEVEL INFLOW TO
SUGGEST RAPID INTENSIFICATION AT ANY POINT FROM HAWAI'I
NORTHEASTWARD---INTO THE WEST COAST. AT THIS POINT...THIS SUGGESTS
A POSITIVELY-TILTED TROUGH CONFIGURATION.

THE EQUATORWARD MOVEMENT OF THE PATTERN WILL ALLOW ANOTHER
MID-LEVEL CYCLONE TO DEVELOP IN THE BERING SEA...WITH COLD
MARITIME AIR PULLED SOUTHWARD AND WEAK WARM ADVECTION IMPULSES
EJECTING EASTWARD OFF THE COAST OF NORTHERN JAPAN AND MIGRATING
TOWARDS THE WESTERN ALEUTIANS. HERE...THE ECENS/GEFS HAVE DECENT
'AGREED-UPON' LONGITUDES FOR THE FORMATION OF THE UPPER-LEVEL
TROUGH BY THE DAY 7-8 TIME FRAME. THIS 'NEW' BERING SEA TROUGH
SHOULD START BRINGING AN INCREASE IN CLOUDINESS...WIND AND LIGHT
PRECIPITATION TO THE ENTIRE ISLAND CHAIN BY THE MIDDLE OF NEXT
WEEK.

VOJTESAK