Prognostic Meteorological Discussion
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FXAK02 KWNH 061835
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
233 PM EDT WED MAY 06 2015

VALID 12Z SUN MAY 10 2015 - 12Z THU MAY 14 2015

AT LEAST INTO THE MIDDLE OF NEXT WEEK MOST GUIDANCE EXPECTS
PERSISTENT MEAN RIDGING OVER WRN CANADA AND TROUGHING OVER THE
EXTREME NERN PAC... WITH THE LATTER COMPOSED OF AN INITIAL UPR LOW
AND THEN SOME COMBINATION OF BERING SEA/NRN PAC ENERGY.  SOME
DEGREE OF RIDGING IS ALSO FCST OVER THE MAINLAND ON MOST DAYS.
MEANWHILE MULTIPLE ENERGETIC FEATURES EMERGING FROM ERN ASIA AND
THE WRN PAC SHOULD YIELD A BROADENING AXIS OF LOW HGTS ALOFT AND
LOW PRES AT THE SFC ALIGNED NEAR THE ALEUTIANS FOR MOST OF NEXT
WEEK.

EARLY IN THE PERIOD THE PRIMARY DIFFICULTIES WILL BE WITH SMALLER
SCALE DETAILS SFC/ALOFT FROM THE BERING SEA INTO NRN-NERN PAC.
FOR THE INITIAL BERING SEA/ALEUTIANS SYSTEM... THE SPREAD IN
LATITUDE FROM GUIDANCE YDAY HAS TRENDED A LITTLE MORE FIRMLY IN
THE DIRECTION OF A TRACK INTO THE BERING SEA BUT STILL WITH A
BROAD ENVELOPE.  THE 00Z-06Z GEFS MEANS ARE NOW THE FARTHEST SWD
SOLNS.  THE 12Z GFS OFFERS A GOOD INTERMEDIATE SOLN IN LIGHT OF
FAST TIMING IN THE 00Z ECMWF/ECMWF MEAN AND STRONG/N-NW CMC-UKMET
RUNS BUT DIVERGENT IDEAS BTWN 00Z-06Z GFS RUNS.  AT THE SAME TIME
AN INITIAL NERN PAC SFC LOW SHOULD WEAKEN QUICKLY WITH THE
APPROACH OF UPSTREAM NRN PAC ENERGY/ASSOC SFC WAVE.  OPERATIONAL
MDLS HOLD ONTO BETTER DEFINITION OF THE INITIAL WAVE WHILE IT
EXISTS SUN.  THE ENSMEANS OFFER A GOOD COMPROMISE FOR THE NEXT
WAVE REACHING THE NERN PAC.

FARTHER UPSTREAM THE ENSEMBLE MEANS REMAIN THE BEST OPTION FOR THE
AREA OF LOW PRES TRACKING INTO THE ALEUTIANS... AS INDIVIDUAL
MODEL RUNS AND ENSEMBLE MEMBERS VARY CONSIDERABLY WITH ONE OR MORE
SFC LOWS ASSOC WITH THE MULTIPLE BUNDLES OF ENERGY EMERGING INTO
THE WRN PAC.  THERE MAY END UP BEING BETTER DEFINED SEPARATE
FEATURES THAN CURRENTLY DEPICTED IN THE MEANS BUT AT LEAST EVEN
THE MEANS SUGGEST THERE WILL BE ONE SYSTEM FROM EARLY IN THE WEEK
ONWARD WITH A TRAILING SYSTEM REACHING THE LONGER TERM MEAN LOW
POSN ON DAY 8 THU.  A BLEND OF THE 00Z ECMWF MEAN AND SLIGHTLY
DEEPER BUT FASTER 06Z GEFS MEAN SEEMS REASONABLE AT THIS TIME.

THE ENSEMBLE MEANS ARE ALSO MORE APPEALING OVER THE MAINLAND BY
MID-LATE PERIOD AS THEY HAVE BEEN MORE SIMILAR AND CONSISTENT WITH
THE IDEA OF A RIDGE EXTENDING ACROSS THE MAINLAND.  THE ENSMEAN
CLUSTER AND OTHER SOLNS SUGGEST THE DAY 8 THU CLOSED LOW OF THE
00Z ECMWF IS A RATHER LOW PROBABILITY SOLN.

BASED ON THE ABOVE CONSIDERATIONS THE DAY 4 SUN FCST STARTS WITH
THE 12Z GFS... WITH HALF INCLUSION OF THE 06Z GEFS/00Z ECMWF MEANS
EARLY MON AS A TRANSITION TO A PURELY ENSMEAN BLEND FOR THE REST
OF THE PERIOD.

RAUSCH

$$





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