Prognostic Meteorological Discussion
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FXAK02 KWNH 291856
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 PM EDT MON MAY 29 2017

VALID 12Z FRI JUN 02 2017 - 12Z TUE JUN 06 2017

CONFIDENCE REMAINS LOWER THAN DESIRED FOR SIGNIFICANT ASPECTS OF
FLOW AT THE SFC AND ALOFT, THOUGH AT LEAST SOME OF THE ENSEMBLE
MEANS HAVE HAD SUFFICIENT AGREEMENT/CONTINUITY TO PROVIDE A
FOUNDATION FOR THE FCST WHILE WAITING FOR A BETTER CONSENSUS TO
EMERGE.

THE AREA FROM THE NRN PAC/ALEUTIANS/SRN BERING SEA EXTENDING EWD
THROUGH THE PANHANDLE HAS BEEN THE GREATEST FOCUS FOR UNCERTAINTY.
 AS OF THE 00Z/06Z CYCLE MODELS/ENSEMBLES WERE STILL AT ODDS OVER
WHAT PROPORTION OF SHORT RANGE ALEUTIANS CLOSED LOW ENERGY WILL
REMAIN OVER THE REGION, LIKELY TO INTERACT WITH ENERGY IMMEDIATELY
UPSTREAM, VERSUS CONTINUE INTO THE NERN PAC PSBLY TO INTERACT WITH
LEADING ENERGY.  THERE IS A DECENT SIGNAL FROM MODELS/MEANS THAT
WHATEVER COMBINATION OF ENERGY ENDS UP AROUND THE ALEUTIANS/NRN
PAC SHOULD CONSOLIDATE INTO AT LEAST A MODERATELY STRONG SYSTEM
OFF THE ERN ALEUTIANS/SWRN ALASKA PENINSULA, THOUGH WITH VARIOUS
INFLUENCES THAT PRODUCE MEANINGFUL SPREAD FOR EVOLUTION/TRACK.
THESE INCLUDE INPUT FROM LOW-PREDICTABILITY PROGRESSIVE
MID-LATITUDE PAC FLOW, AS WELL AS DIFFS IN HOW MUCH RIDGING MAY
CROSS THE BERING SEA WITH CORRESPONDING INFLUENCE ON LATITUDE OF
THE SFC LOW TRACK.  THE NEW 12Z MODEL RUNS INCLUDING THE ECMWF
SHOW A MORE PRONOUNCED CLUSTERING TOWARD BRINGING THE ENTIRE SHORT
RANGE ALEUTIANS UPR LOW INTO THE NERN PAC WITH UPSTREAM ENERGY
PROVIDING THE EXCLUSIVE SUPPORT FOR THE DEVELOPMENT TO THE S OF
THE ALEUTIANS.

MEANWHILE GFS RUNS HAVE TENDED TO BE MORE EAGER TO BRING THE MEAN
UPR LOW OVER THE NERN PAC MORE E/NE INTO THE PANHANDLE AND NWRN
CANADA THAN RECOMMENDED BY MOST OTHER SOLNS.  ENSEMBLE MEANS HAVE
BEEN CONSISTENT OVER MULTIPLE DAYS IN SHOWING A PERSISTENT MEAN
RIDGE FROM CANADA ACROSS THE MAINLAND, WITH THE AXIS OF THE
MAINLAND PART OF THE RIDGE LIKELY DRIFTING A LITTLE NWD WITH TIME.
 THE ENSEMBLE MEAN DEPICTION APPEARS FAIRLY WELL SUPPORTED BY
TELECONNECTIONS RELATIVE TO BEST DEFINED ERN PAC AND NORTH
AMERICAN FEATURES MID-LATE PERIOD.  BASED ON GUIDANCE THROUGH THE
06Z CYCLE THE 00Z ECMWF/CMC IDEA OF HAVING SOME OF THE NERN PAC
ENERGY PASS OVER/S OF THE SRN PANHANDLE ON ITS WAY INTO SWRN
CANADA SEEMED MORE PLAUSIBLE.  HOWEVER THE NEW 12Z CONSENSUS OF
HAVING MORE UPR LOW ENERGY TRACK INTO THE NERN PAC EARLIER IN THE
PERIOD DOES INCREASE THE POTENTIAL FOR STRONGER HGT FALLS TO CROSS
THE PANHANDLE AFTER DAY 6 SUN.

ALBEIT WITH SOME MODEST RUN-RUN TIMING ADJUSTMENTS, THE ECMWF MEAN
IS CURRENTLY THE MOST STABLE SOLN WITH THE WRN PAC SYSTEM THAT MAY
REACH THE WRN ALEUTIANS BY DAY 8 TUE.  00Z AND ESPECIALLY 06Z GEFS
MEAN RUNS HAVE TRENDED SLOWER BUT THE 00Z CMC MEAN AGREED WITH THE
ECMWF MEAN.  AMONG INDIVIDUAL SOLNS THERE IS A LOT OF SPREAD
REGARDING PSBL STREAM INTERACTION ALOFT FROM ERN SIBERIA SWD INTO
THE MID-LATITUDES OVER THE COURSE OF THE PERIOD SO IT WOULD NOT BE
SURPRISING TO SEE CONTINUED SPREAD AND SOME SIGNIFICANT CONTINUITY
CHANGES IN FUTURE RUNS.

BASED ON GUIDANCE THROUGH THE 06Z CYCLE ALONG WITH CONTINUITY
CONSIDERATIONS, THE 00Z ECMWF/ECMWF MEAN/NAEFS MEAN PROVIDED THE
PREFERRED STARTING POINT FOR TODAY`S FCST.  THE 00Z ECMWF OFFERED
THE CLOSEST OPERATIONAL COMPARISON TO THE MEANS AND THE NAEFS MEAN
HELPED TO INCORPORATE SOME IDEAS FROM 00Z GEFS/CMC ENSEMBLE
GUIDANCE.

RAUSCH

$$





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