Prognostic Meteorological Discussion
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FXAK02 KWNH 211936
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 PM EST FRI NOV 21 2014

VALID 12Z TUE NOV 25 2014 - 12Z SAT NOV 29 2014

FOR THIS PARTICULAR MEDIUM RANGE FORECAST PERIOD---THE TUE/WED
PERIOD ALONG THE PANHANDLE AND EAST CENTRAL PACIFIC WILL BE THE
CHALLENGING PORTION OF THE FORECAST. OVER THE ALEUTIANS AND
SOUTHERN BERING SEA...THE EMPHASIS WILL BE IN THE LATTER HALF OF
THE FORECAST PERIOD---WHEN A BROAD CYCLONIC MID-LEVEL TO
UPPER-LEVEL CYCLONIC FLOW MIGRATES ACROSS THE REGION. THE 21/00Z
ECENS AND GEFS MEANS WERE GENERALLY ACCEPTED AS THE BASELINE FOR
THE MEDIUM RANGE MASS FIELD FORECASTS.

NOT MUCH CHANGE IN THE DAILY SURFACE GRAPHICS...
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 4-5 PERIOD---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. THE 21/12Z DETERMINISTIC GUIDANCE CONTINUES
TO DISPLAY VERY LARGE SPREAD WITH THE INTENSITY OF AND TRACK OF
SURFACE WAVE DEVELOPMENT ORIGINATING IN THE SUBTROPICS. THE
SYSTEM---BY IN LARGE---ONLY GENERATES PRECIPITATION IN THE
PANHANDLE. THE CHALLENGE IS...HOW INTENSE AND EXACTLY WHERE THE
PRECIPITATION IS LIKELY TO IMPACTS THE LOCAL SENSIBLE WEATHER
CONDITIONS.

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 TROUGHING 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. NOTHING SEEN IN
THE 00Z & 12Z DETERMINISTIC GUIDANCE CONVINCED ME OTHERWISE---AS
THIS DAY 4-5 SYSTEM MIGRATES NORTHEASTWARD INTO THE WEST COAST OF
NORTH AMERICA.

VOJTESAK

$$




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