Prognostic Meteorological Discussion
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FXAK02 KWNH 011943
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
342 PM EDT TUE SEP 01 2015

VALID 12Z SAT SEP 05 2015 - 12Z WED SEP 09 2015

...MODEL AND UNCERTAINTY ASSESSMENT...

THE DETERMINISTIC MODELS OFFER ABOVE AVERAGE FORECAST SPREAD AND
ALSO VERY POOR RUN TO RUN CONTINUITY THROUGH MEDIUM RANGE TIME
SCALES. ENSEMBLE MEANS HAVE PROBLEMS TOO...BUT THESE ARE MUTED IN
COMPARISON. THE LAST FEW GFS RUNS ALSO OFFER QUITE A BIT OF
QUESTIONABLE STREAM FLOW PHASING NEXT WEEK DOWN THROUGH NW/WRN AK
INTO THE ERN BERING SEA. PHASING IN THIS CHAOTIC PATTERN IS NOT
VERY PREDICTABLE AT LONGER TIME FRAMES. CONSIDERING UNCERTAINTY
AND AS PER WFO ANCHORAGE COORDINATION...PREFER AN ENSEMBLE MEAN
FORECAST APPROACH. ACCORDINGLY...THE WPC ALASKAN MEDIUM RANGE
PRODUCT SUITE WAS PRIMARILY DERIVED FROM A BLEND OF 70 PERCENT 00
UTC ECMWF ENSEMBLE MEAN AND 30 PERCENT 00 UTC NAEFS MEAN. OPTED TO
LEAN HEAVIER ON THE ECMWF ENSEMBLE MEAN THAT OFFERS LESS STREAM
FLOW PHASING AS PER ABOVE. WPC CONTINUITY IS LESS THAN NORMAL DUE
TO THE COMPLICATED NATURE OF THE PATTERN.

...OVERALL PATTERN AND SENSIBLE WEATHER HIGHLIGHTS...

THE ALASKA MEDIUM RANGE PERIOD SEEMS TO BEST OFFER A MAIN BERING
SEA/AK PENINSULA TO GULF OF ALASKA/SE AK MAIN STORM
TRACK...CLIPPING THE ALASKAN SRN TIER. A SERIES OF HARD TO
TIME/JUDGE SYSTEMS IN THIS FLOW WOULD LOCALLY ENHANCE PCPN/WEATHER
POTENTIAL...ALBEIT WITH BELOW NORMAL PREDICTABILITY. THE
EXTRATROPICAL REMAINS OF IGNACIO ALSO ARE FORECAST TO ENTRAIN INTO
THE NERN PACIFIC FLOW PATTERN BY NEXT WEEK AS PER THE CENTRAL
PACIFIC HURRICANE CENTER. IGNACIO IS DEPICTED ON THE SRN FRINGE OF
THE WPC ALASKAN SURFACE FRONTS/PRESSURE PROGS DAYS 6-8...BUT
ASSOCIATED MOISTURE MAY FEED FURTHER UP INTO THE GULF OF AK SYSTEM
STREAM INTO NEXT MIDWEEK.

SCHICHTEL



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