Prognostic Meteorological Discussion
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FXAK02 KWNH 041919
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
218 PM EST WED MAR 04 2015

VALID 12Z SUN MAR 08 2015 - 12Z THU MAR 12 2015


THE MODELS AND ENSEMBLES HAVE BEGUN TO DIVERGE IN THE DAYS 4-6
REALM OWING TO SIGNIFICANT TIMING DIFFERENCES IN THE 500 MB TROUGH
AS IT DEPARTS THE BERING SEA AND CROSSES SOUTHERN AK SUNDAY AND
THEN  THE AK PANHANDLE MON AND BEYOND.
THE GFS/GEFS ARE ON THE FASTER TRACK WITH THE OPERATIONAL 00Z
ECMWF/CANADIAN GLOBAL AND THEIR RESPECTIVE ENSEMBLES MEANS SLOWER.
THE 12Z ECMWF HAS TRENDED EVEN SLOWER TO SUPPORT THE EARLIER
FORECAST.
OWING TO LONGER TERM BIAS OF THE GFS MOVING UPPER TROUGHS TOO
QUICKLY...THE FORECAST GAVE MUCH MORE WEIGHTING TO THE
ECMWF/CANADIAN GLOBAL AND THEIR ENSEMBLE MEANS.

EARLY TO MID NEXT WEEK...THE LARGE SCALE PATTERN RE-AMPLIFIES.
THE MODELS/MEANS SHOW A CLOSED LOW NEAR 50N 135E 12Z TUE 10 MAR
THAT PRODUCES AN AMPLIFYING RIDGE INTO THE WESTERN BERING SEA AND
AMPLIFYING TROUGH DOWNSTREAM INTO THE EASTERN BERING SEA AND THEN
MAINLAND AK BY 00Z WED 11 MAR. AT THIS POINT THE GFS CATCHES UP TO
BE IN BETTER AGREEMENT WITH THE ECMWF/CANADIAN GLOBAL IDEA OF AN
AMPLIFYING TROUGH DRIFTING EAST ACROSS MAINLAND AK AND THE HIGH
AMPLITUDE RIDGE COVERING THE BERING SEA.  THIS HAS THE APPEARANCE
OF A BLOCKING PATTERN SETTING UP.  THE AMPLIFYING TROUGH ALSO
LEADS TO A PERIOD OF BELOW NORMAL TEMPERATURES IN CENTRAL TO
NORTHERN AK NEXT WEEK...EXPANDING SOUTH AS THE WEEK PROGRESSES.

PETERSEN

$$




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