Prognostic Meteorological Discussion
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FXAK02 KWNH 031905
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 PM EDT MON AUG 03 2015

VALID 12Z FRI AUG 07 2015 - 12Z TUE AUG 11 2015

TODAY`S FCST REPRESENTS A BALANCING ACT BTWN DIFFERING PREFERRED
SOLN CLUSTERS FOR THE UPR TROUGH/EMBEDDED CLOSED LOW APPROACHING
THE NWRN MAINLAND AND THE SYSTEM EXPECTED TO TRACK FROM THE
ALEUTIANS THROUGH THE BERING SEA.

FROM THE MULTI-DAY PERSPECTIVE CONSENSUS HAS MAINTAINED DECENT
CONTINUITY WITH THE HIGHER LATITUDE UPR TROUGH.  THUS FAR MOST
OPERATIONAL MODELS HAVE BEEN LEADING THE ENSEMBLE MEANS IN
SIGNALING THE DEPTH OF THE EMBEDDED CLOSED LOW... AND STILL SHOW A
DEEPER UPR LOW THAN FCST BY LATEST MEANS.  IN THE LATEST CYCLE OF
GUIDANCE THE 00Z ECMWF BRINGS THE UPR LOW FARTHER E/SE THAN MOST
OTHER SOLNS.  THE FULL ECMWF ENSEMBLE ENVELOPE CONTAINS THE
OPERATIONAL RUN BUT OTHERWISE CONFIDENCE IS SUFFICIENTLY LOW TO
FAVOR LEANING AWAY FROM EXACT DETAILS OF THE 00Z ECMWF OVER AND
N/NW OF THE NRN MAINLAND.  12Z MODEL RUNS OFFER FURTHER SUPPORT
FOR RESTRAINING THE HGT FALLS SEEN IN THE 00Z ECMWF.

SOME DETAIL QUESTIONS REMAIN FOR EXACTLY HOW THE ALEUTIANS/BERING
SEA SYSTEM WILL EVOLVE.  SOME GFS RUNS HAVE BEEN ON THE
PROGRESSIVE SIDE WHETHER WITH THE PRIMARY SYSTEM OR WITH A LEADING
WAVE THAT ULTIMATELY BECOMES THE DOMINANT SFC LOW.  WHILE THE 00Z
ECMWF IDEA OF MAINTAINING A SLOWER/BETTER DEFINED PRIMARY LOW
SEEMS REASONABLE AND HAS SUPPORT FROM THE 00Z UKMET THROUGH ITS
RUN AND THE 00Z CMC MEAN... THAT SPECIFIC RUN IS SOMEWHAT SLOWER
THAN PREVIOUS ECMWF RUNS AND ECMWF MEANS.  MULTI-DAY TRENDS OF THE
ENSEMBLE MEANS HAVE SUGGESTED SOME DEGREE OF FASTER PROGRESSION SO
PREFER TO NUDGE THE 00Z ECMWF SOLN A LITTLE FASTER.

AN ONGOING UNCERTAINTY BY THE LATTER HALF OF THE PERIOD IS THE
EXTENT TO WHICH THE NRN STREAM TROUGH INTERACTS WITH THE
ALEUTIANS/BERING SEA SYSTEM.  CURRENTLY EXPECT A REASONABLE DEGREE
OF SEPARATION THROUGH AT LEAST DAY 6 SUN WITH GREATER SOLN SPREAD
THEREAFTER.  AS TENDS TO BE THE CASE THE ENSEMBLE MEANS BEGIN TO
SHOW MORE STREAM INTERACTION BY MON-TUE.  THE MOST LIKELY SCENARIO
MIGHT BE A LESS PHASED SOLN THAN THE MEANS BUT WITH ONE OR MORE
SHRTWVS WITHIN NRN STREAM FLOW STILL HAVING SOME DEGREE OF
INFLUENCE ON THE BERING SEA SYSTEM.

AHEAD OF THE PRIMARY FEATURES OF THE EXTENDED PERIOD... A
MODEL/ENSMEAN CONSENSUS LOOKS REASONABLE FOR THE SYSTEM OVER THE
EXTREME NERN PAC AS OF DAY 4 FRI.  SUCH A SOLN RESOLVES CURRENT
SPREAD AMONG A MAJORITY CLUSTER THAT KEEPS THE SYSTEM FARTHER
OFFSHORE THAN THE 00Z GFS.

PREFS DESCRIBED ABOVE LEAD TO A STARTING BLEND THAT INCLUDES SOME
00Z ECMWF AND ECMWF MEAN GUIDANCE THROUGH THE PERIOD ALONG WITH
THE 12Z GFS THROUGH 12Z SAT FOLLOWED BY A TRANSITION TO THE 06Z
GEFS MEAN FOR THAT COMPONENT OF THE BLEND.  MINOR MANUAL
ADJUSTMENTS ATTEMPTED TO BRING THE INITIAL BLEND A LITTLE CLOSER
TO THE DESIRED FCST FOR THE FEATURE OF INTEREST.

RAUSCH

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