Prognostic Meteorological Discussion
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FXAK02 KWNH 271828
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
127 PM EST SAT DEC 27 2014

VALID 12Z WED DEC 31 2014 - 12Z SUN JAN 04 2015

SPRAWLING HIGH PRESSURE ALOFT AND AT THE SURFACE WILL PREVAIL OVER
MUCH OF THE INTERIOR AND NORTHERN GULF OF ALASKA THIS MEDIUM RANGE
PERIOD. TELECONNECTIONS INTO DAY 8 AND BEYOND---KEEP A BROAD
UPPER-LEVEL RIDGE FIXED OVER THE NORTH CENTRAL GULF OF
ALASKA---WITH MUCH IF NOT ALL---PACIFIC MOISTURE AND
WEATHER-MAKING POTENTIAL SHUNTED WEST OF THE DATELINE AND ALONG
THE SOUTHERN PERIPHERY OF THE BROAD UPPER HIGH.

A BROAD AND DEEP TROUGH IS EXPECTED TO REMAIN ALONG/WEST OF THE
DATELINE WITH ENERGY ROTATING NORTHWARD ACROSS THE WESTERN HALF OF
THE ALEUTIANS. EARLY IN THE MEDIUM RANGE PERIOD---A SHORTWAVE WILL
BRUSH THE WEST COAST BEFORE MOVING NORTHWARD INTO THE BERING
STRAIT AND NORTHEAST SIBERIA. BUT AFTER THIS SYSTEM---VERY LITTLE
IS EXPECTED TO CHANGE IN THE SENSIBLE WEATHER PATTERN.

AT LEAST UNTIL THE DAY 7-8 PERIOD...WHEN THE UPPER-LEVEL RIDGE HAS
COMPLETED A WESTWARD RETROGRESSION OVER WESTERN CANADA AND THE
ARCTIC CIRCLE---AND EXPANSION OF THE ARCTIC AIRMASS INTO THE FAR
NORTHEASTERN PACIFIC OCEAN HAS CEASED. AT THAT POINT IN
TIME...NORTH CENTRAL PACIFIC FLOW WILL SLOWLY UNDERCUT THE UPPER
RIDGE AND A WAVE TRAIN WILL BEGIN TO EMERGE IN THE EAST CENTRAL
PACIFIC---ALONG 45N-50N LATITUDE.

THE SURFACE AND 500MB GRAPHICS WERE CREATED USING A GREAT DEAL OF
THE 27/00Z ECENS MEAN---WHICH CONTINUES TO BE A VERY STABLE PIECE
OF FORECAST GUIDANCE ACROSS THE PACIFIC OCEAN AND HIGH-LATITUDE
NORTH AMERICA. THE 27/00Z GEFS CONTINUES TO DISPLAY A FAST BIAS IN
THE CENTRAL PACIFIC AND SUBTROPICS WITH ENERGY MOVING NORTHWARD
ALONG 155W LONGITUDE---FROM 30N TO 50N LATITUDE. WITH THE PATTERN
AMPLIFYING OVER THE WESTERN COAST OF NORTH AMERICA---THE FASTER
GEFS/GFS HAS HAD A TENDENCY TO MIGRATE TOO MUCH ENERGY
EASTWARD---AND INTO THE RIDGE.

THE MEDIUM RANGE CHALLENGE---IF THERE IS ONE---WILL BE TO
DETERMINE WHEN/WHERE CENTRAL PACIFIC ENERGY CAN BECOME ENTRAINED
INTO THE RETROGRADING MID-LATITUDE FLOW PATTERN.

VOJTESAK



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