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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1810Z Feb 21, 2015)
 
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
110 PM EST SAT FEB 21 2015

VALID 12Z WED FEB 25 2015 - 12Z SUN MAR 01 2015

MODELS AND ENSEMBLES STILL SHOW THAT SHORT RANGE HIGH AMPLITUDE
FLOW OVER THE MID-UPPER LATITUDES NEAR ALASKA TRANSITIONS INTO
MEDIUM RANGE TIME SCALES NEXT WEEK. FORECAST UNCERTAINTY INCREASES
THROUGH MIDWEEK AS BERING SEA SYSTEM ENERGY ALONG WITH HEIGHT
FALLS AND SOME COOLING/PCPN WORKS INCREASINGLY ENEWD THROUGH AN
AMBIENT DOWNSTREAM RIDGE BUILT UP THROUGH THE INTERIOR. HAVE BEEN
RELUCTANT TO BREAK INTO THE RIDGE TOO STRONGLY...AND THAT
CONTINUES TO BE A BETTER FIT WITH LATEST GUIDANCE TRENDS.

UNDERNEATH... THE DETERMINISTIC GFS/ECMWF HAVE COME INTO BETTER
AGREEMENT OVER THE PAST COUPLE OF DAYS WITH SOMEHWAT MORE
ORGANIZED AND SLIGHTLY LESS PROGRESSIVE TRENDING PACIFIC LOW
ENERGIES THAT WORK ACROSS THE GULF OF ALASKA INTO WED/THU THAT
LEAD TO MODEST DOWNSTREAM INFLOW/PCPN INTO SRN/SERN AK. THESE
GUIDANCE FORECAST SYSTEMS SEEM TO EXTEND WELL FROM LATEST WATER
VAPOR LOOPS.

AN ALASKAN RIDGE REBUILDS STRONGLY LATER NEXT WEEK UP THROUGH MUCH
OF THE STATE IN RESPONSE TO AMPLIFIED UPSTREAM TROUGH ALOFT/DEEP
SURFACE LOW ENERGY APPROACH TO THE BERING SEA THAT SEEMS WELL
SUPPORTED BY LATEST WATER VAPOR IMAGERY. HOWEVER...EVEN THE
ENSEMBLE MEANS DIFFER SOME WITH THE EXTENT OF AMPLIFICATION INTO
NRN LATITUDES AND CONSIDERING UNCERTAINTY PREFER A COMPOSITE
SOLUTION.  

THE 06 UTC GFS AND 00 UTC ECMWF DETERMINISTIC RUNS ARE IN DECENT
AGREEMENT INTO TUE/WED AND AS SUCH HAVE BEEN HEAVILY INCLUDED IN
THE WPC SOLUTION MIX TO ADD DETAIL. DID ALSO INCLUDE MEAGER INPUTS
FROM THE 06 UTC GFS MEAN AND ECMWF/NAEFS ENSEMBLE MEANS FOR
CONTINUITY. STILL PREFER A MORE RUN TO RUN CONSISTENT SOLUTION
WITH THESE ENSEMBLE MEANS BLENDED FORECAST APPROACH AT LONGER TIME
SCALES THAT PLACES EMPHASIS ON THE MORE PREDICTABILE MEDIUM TO
LARGER SCALE FORECAST COMPONENTS. THIS ALSO MAINTAINS GOOD WPC
CONTINUITY.

SCHICHTEL