Prognostic Meteorological Discussion
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FXAK02 KWNH 251829
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
228 PM EDT MON MAY 25 2015

VALID 12Z FRI MAY 29 2015 - 12Z TUE JUN 02 2015

OVER THE MAINLAND AND VICINITY THERE IS CONTINUING UNCERTAINTY
REGARDING THE EVOLUTION OF MEAN RIDGING FCST TO EXTEND FROM THE
NERN PAC N/NW THROUGH AND BEYOND THE MAINLAND... AND IN TURN FOR
EMBEDDED/SURROUNDING SHRTWV ENERGY.  ONE POSITIVE TREND OVER THE
PAST DAY IS THAT THE OPERATIONAL ECMWF NOW HOLDS ONTO STRONGER
RIDGING OVER THE MAINLAND WHICH HAS BEEN ADVERTISED MORE
CONSISTENTLY IN THE ENSEMBLE MEANS.  THE 00Z UKMET/CMC AGREE WITH
THE ECMWF AND LATEST ENSMEAN IDEA THAT INITIAL SHRTWV ENERGY OVER
THE MAINLAND SHOULD PROGRESS FARTHER EWD THAN DEPICTED IN THE
00Z/06Z GFS.  THE 12Z GFS HAS TRENDED TOWARD BUT NOT QUITE TO THE
MAJORITY CLUSTER.  BY MID-LATE PERIOD THERE IS SOME
DISAGREEMENT/WAFFLING WITH RESPECT TO WHETHER AN UPR HIGH WILL
CLOSE OFF TO THE NW OF THE MAINLAND AND AS A RESULT ALLOW A
WEAKNESS TO FORM OVER THE MAINLAND ITSELF.  IN THE PAST COUPLE
DAYS OR SO THE GEFS MEANS HAVE TENDED TO BE MORE EAGER TO CLOSE
OFF A HIGH CENTER BUT SOME RECENT ECMWF MEAN RUNS ALSO SHOWED A
CLOSED CENTER BEFORE TRENDING BACK TO AN OPEN RIDGE IN THE CURRENT
00Z CYCLE.  ONE CONSISTENT THEME FROM THE MEANS REGARDLESS OF THIS
DETAIL IS A GENERAL LACK OF SUPPORT FOR PRONOUNCED LOWERING OF
MAINLAND AND/OR SRN COAST-PANHANDLE HGTS THAT HAS BEEN DEPICTED IN
SOME RECENT OR CURRENT GFS/ECMWF/CMC OPERATIONAL RUNS.  CONTINUE
TO PREFER THE ENSEMBLE MEANS FOR THE MID-LATE PART OF THE FCST
PERIOD.

GUIDANCE HAS BEEN QUITE VARIABLE FROM THE NRN PAC INTO THE BERING
SEA.  FOR THE LEADING SYSTEM REACHING THE BERING SEA AS OF DAY 4
FRI THERE IS A PRONOUNCED WWD ADJUSTMENT COMPARED TO PAST DAYS.
TO VARIOUS DEGREES THE LATEST MODELS/ENSEMBLES AGREE WITH THIS
ADJUSTMENT SO THIS TREND IS ACCEPTED.  FOR THE SECOND SYSTEM
COMING INTO THE PICTURE BY DAYS 7-8 MON-TUE... LEADING INTO YDAY
THERE WAS A LACK OF DEPENDABLE AGREEMENT/CONTINUITY WITH THE 00Z
ECMWF MEAN SOMEWHAT ON ITS OWN.  HOWEVER THE ECMWF MEAN HAS
MAINTAINED FAIR CONSISTENCY WITH ITS SOLN AND REMAINING GUIDANCE
HAS GENERALLY ADJUSTED IN ITS DIRECTION.  THE 00Z NAEFS/06Z GEFS
MEANS ARE SOMEWHAT DEEPER WITH THE SFC REFLECTION SO INCLUSION OF
THEIR SOLNS IN THE BLEND ALONG WITH THE ECMWF MEAN WILL HELP TO
IMPROVE INITIAL DEFINITION OF THE SYSTEM BEFORE MANUAL ADJUSTMENT.

DAYS 4-5 FRI-SAT START WITH A COMPROMISE AMONG THE 00Z ECMWF/UKMET
AND NAEFS/ECMWF MEANS TO YIELD A GOOD INTERMEDIATE SOLN FOR THE
INITIAL BERING SEA SYSTEM AND REPRESENT NON-GFS PREFS OVER THE
MAINLAND.  DAYS 6-8 SUN-TUE EMPHASIZE THE 00Z ECMWF MEAN AND 00Z
NAEFS/06Z GEFS MEANS GIVEN RELATIVELY BETTER STABILITY OVER/NEAR
THE MAINLAND VERSUS OPERATIONAL RUNS... WHILE THE LATTER SOLNS
NUDGE THE LATE PERIOD NRN PAC/ALEUTIANS SYSTEM STRONGER THAN THE
ECMWF MEAN.

RAUSCH

$$




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