Prognostic Meteorological Discussion
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FXAK02 KWNH 231917
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
317 PM EDT FRI JUN 23 2017

VALID 12Z TUE JUN 27 2017 - 12Z SAT JUL 01 2017

FROM THE LARGE SCALE PERSPECTIVE, TODAY`S GUIDANCE SHOWS BETTER
THAN AVG AGREEMENT REGARDING A FAIRLY BLOCKY/SLOW TO EVOLVE
PATTERN DOMINATED BY A MEAN UPR LOW CENTERED OVER THE BERING SEA
AND STRONG RIDGE WITH AN AXIS EXTENDING THROUGH WRN CANADA.  FCST
UNCERTAINTIES FOCUS ON DETAILS WITHIN THE MEAN LOW AND ON ONE OR
MORE WAVES FROM THE MID-LATITUDE PACIFIC INTO THE NERN PAC/GULF OF
ALASKA.  EXPECT THESE WAVES TO HAVE LOW PREDICTABILITY FOR
SPECIFICS DUE TO SUPPORTING ENERGY ALOFT CONSISTING OF LOW
AMPLITUDE RIPPLES EMBEDDED WITHIN FAST FLOW ALOFT.

THE MID-LATITUDE PAC WAVE THAT HAS THE BEST SIGNAL IN A RELATIVE
SENSE SHOULD REACH NOT FAR FROM KODIAK ISLAND IN THE WED-THU TIME
FRAME.  OFFSETTING CONSIDERATIONS SEEM TO FAVOR A COMPROMISE TRACK
FOR THIS WAVE.  00Z GFS/ECMWF RUNS HAVE NUDGED A BIT TO THE RIGHT
FROM 24 HRS AGO.  HOWEVER THE ERN SIDE OF THE FULL ENSEMBLE SPREAD
HAS COME BACK WWD A BIT, THE 00Z UKMET/CMC HOLD ONTO A FARTHER W
TRACK, AND DOWNSTREAM RIDGING ALOFT APPEARS STRONG ENOUGH TO LEAN
SOMEWHAT AWAY FROM ANY SOLN ON THE MOST ERN SIDE OF THE ENVELOPE.
THUS TODAY`S FCST INCORPORATED 25-30 PCT OF THE 00Z CMC TO PULL
BACK THE 00Z GFS/ECMWF A LITTLE.  06Z/12Z GFS RUNS SEEMED FAST BUT
AT LEAST THE 12Z RUN TRENDED A LITTLE WWD ONCE NEAR KODIAK ISLAND.
 REMAINING 12Z GUIDANCE ARRIVING AFTER FCST PREPARATION IS STILL
DIVERSE IN STRENGTH AND TRACK.

THERE WILL LIKELY BE ANOTHER TRAILING WAVE THAT COMES INTO THE
PICTURE MID-LATE PERIOD.  THE BEST OPTION TO REPRESENT EXISTENCE
OF SUCH A WAVE WAS TO USE A MODEST WEIGHT OF 00Z GFS/ECMWF/CMC
RUNS TO YIELD A FEATURE SOMEWHAT BETTER DEFINED THAN IN THE
ENSEMBLE MEANS BUT STILL RELATIVELY WEAK, ULTIMATELY TRACKING INTO
A GENERAL SFC WEAKNESS WHICH THE MEANS HAVE NEAR KODIAK ISLAND BY
DAY 8 SAT.  BY LATE IN THE PERIOD INDIVIDUAL MODEL RUNS ALSO
DIVERGE WITH RESPECT TO BERING SEA UPR LOW ENERGY AND SURROUNDING
FLOW, WITH INTERACTION POTENTIAL FOR ANY MID-LATITUDE PAC WAVE
THAT DEVELOPS LEADING TO ADDED FCST COMPLEXITY.  NEEDLESS TO SAY
CONFIDENCE IS RATHER LOW FOR FCST DETAILS ACROSS THE NRN-NERN PAC
BY DAYS 7-8 FRI-SAT.

BASED ON FCST PREFS TODAY`S BLEND STARTED WITH THE 00Z
GFS/ECMWF/CMC DAYS 4-5 TUE-WED WITH GRADUALLY INCREASING 06Z
GEFS/00Z ECMWF MEAN WEIGHT THEREAFTER TO CAPTURE THE LARGE SCALE
AGREEMENT AND DOWNPLAY LOWER CONFIDENCE ASPECTS OF SYSTEM
EVOLUTION.

RAUSCH

$$




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