ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
207 PM EDT SUN MAY 19 2013

VALID 12Z THU MAY 23 2013 - 12Z MON MAY 27 2013

MODELS AND ENSEMBLES CONTINUE TO VARY IN THEIR HANDLING OF NRN
STREAM FLOW AROUND A BERING SEA CLOSED LOW AS OF EARLY THU AND
MID-LATITUDE ENERGY ACROSS THE PACIFIC... ALONG WITH THE
INTERACTION OF THESE TWO STREAMS.  AT THE MOMENT THERE IS DECENT
AGREEMENT IN PRINCIPLE TOWARD A MEAN CLOSED LOW ALOFT OVER THE
ALEUTIANS OR BERING SEA BY DAYS 6-8 SAT-MON.  HOWEVER CONFIDENCE
IS BELOW AVG GIVEN THAT THE 00Z ENSEMBLE MEANS/06Z GEFS MEAN
REPRESENT A SIGNIFICANT CHANGE IN CONTINUITY FROM EARLIER RUNS AND
OPERATIONAL MODEL DETAILS HAVE NOT BEEN CONSISTENT THUS FAR.  IN
ADDITION THERE IS STILL CONSIDERABLE DIFFICULTY IN RESOLVING WHICH
PIECE OF ENERGY OVER THE PAC AS OF THE START OF THE PERIOD WILL
ULTIMATELY DEVELOP THE MOST. 

THE MOST COMMON THEME IN LATEST GUIDANCE IS TOWARD NWD EJECTION OF
AT LEAST SOME OF THE ENERGY INITIALLY ASSOC WITH THE BERING SEA
CLOSED LOW AS FLOW TO THE W INTERACTS WITH PACIFIC ENERGY TO YIELD
THE CLOSED LOW FCST DURING THE LATTER HALF OF THE PERIOD.  THE 00Z
ECMWF... WHICH TRACKS THE INITIAL BERING SEA ENERGY WELL EWD OF
OTHER GUIDANCE AND ACROSS THE MAINLAND... IS MOST AT ODDS WITH
OTHER SOLNS THAT BUILD A DECENT RIDGE OVER THE MAINLAND BY
SUN-MON.  THE 06Z GFS KEEPS THE INITIAL BERING SEA CLOSED LOW IN
PLACE THROUGH FRI INSTEAD OF LIFTING IT NWD... BUT WITH ONLY
MODEST IMPACT ON THE PATTERN OVER THE MAINLAND.

THE RELATIVE LACK OF CONFIDENCE IN THE TRACK OF LOW PRESSURE
HEADING TOWARD THE ALEUTIANS IS HIGHLIGHTED BY THE FACT THAT THE
00Z GEFS SPREAD EXTENDS AS FAR WWD AS THE 00Z ECMWF/ECMWF MEAN...
WHILE THE ECMWF ENSEMBLE SPREAD EXTENDS FAR ENOUGH EWD TO INCLUDE
THE LATEST GFS/GEFS MEAN RUNS.  THE GEFS/ECMWF MEANS CONVERGE TO
SOME DEGREE ONCE THE SYSTEM REACHES THE BERING SEA.

AT LEAST INTO DAY 6 SAT THE 12Z GFS OFFERS A WWD COMPROMISE FROM
00Z/06Z GFS RUNS WITH THE PAC SYS HEADING TOWARD THE ALEUTIANS...
PERHAPS A TAD SLOW/SWD BUT OTHERWISE REASONABLE AS A MINORITY
COMPONENT OF A BLEND WITH THE 00Z ECMWF MEAN AND NAEFS MEAN. 
HANDLING OF THE BERING SEA CLOSED LOW IS STILL A QUESTION MARK
MID-LATE PERIOD IN THE 12Z GFS AND THE MODEL RUN ERODES THE
CONSENSUS RIDGE ALOFT OVER THE MAINLAND... SO DAYS 7-8 SUN-MON
FOLLOW A SOLN CLOSE TO THE 00Z ECMWF MEAN AS THE CLEANEST
REPRESENTATION OF THE PREFERRED PATTERN AT THAT TIME.

RAUSCH