Prognostic Meteorological Discussion
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FXAK02 KWNH 201801
PMDAK

ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EDT SUN AUG 20 2017

VALID 12Z THU AUG 24 2017 - 12Z MON AUG 28 2017

...GUIDANCE ASSESSMENT AND PREDICTABILITY...

TODAYS WPC ALASKAN MEDIUM RANGE SURFACE FRONTS/PRESSURES...500 MB
PROGS...AND SENSIBLE WEATHER GRIDS WERE MAINLY DERIVED FROM THE 00
UTC ECMWF DAYS 4-6 THU-SAT THAT HAS GOOD ENSEMBLE SUPPORT. OPTED
TO TRANSITION TO ENSEMBLE MEANS STARTING NEXT SUN AMID GROWING
FORECAST SPREAD AND UNCERTAINTY. LEANED MOSTLY ON THE 00 UTC ECMWF
ENSEMBLE MEAN AND TO A LESSER EXTENT THE 00 UTC NAEFS MEAN FOR
CONTINUITY.

...FORECAST PATTERN AND WEATHER HIGHLIGHTS...

A SLOW TO DISLODGE SRN ARCTIC CLOSED LOW AND ASSOCIATED SURFACE
FRONTAL SYSTEM TRAILING TO THE NORTH SLOPE AND NRN INTERIOR
LINGERING INTO THURSDAY IS EXPECTED TO LIFT TOWARD THE POLE
THEREAFTER...ALONG WITH AN ASSOCIATED PERIOD OF UNSETTLED WEATHER.

WELL UNDERNEATH...A CLOSED LOW ALOFT DUG INTO HAIDA
GWAII/VANCOUVER ISLAND AND HIGHLY ANOMOLOUS LEAD DEEP
MOISTURE/HEAVY PRECIPITATION WILL WORK INCREASING AWAY FROM THE
STATE INTO BRITISH COLUMBIA BY EARLY THURSDAY.

MEANWHILE...AN AMPLIFIED SERN BERING SEA/ALEUTIANS/SW AK MID-UPPER
LEVEL TROUGH AND DEEPENED SURFACE LOW/FRONTAL SYSTEM WILL PRODUCE
HIGHLY UNSETTLED SEAS AND WEATHER THURSDAY. ENERGY TRANSFER SHOULD
FORCE WELL ORGANIZED LOW DEVELOPMENT SEWD INTO THE GULF OF AK
FRI-NEXT SUN/MON...PROMPTING HEAVY RAINFALL POTENTIAL INTO SRN
THEN SERN AK ALONG WITH UNSETTLED WEATHER/SEAS. THIS OCCURS AS
ENERGETIC BUT MORE UNCERTAIN AND MORE PROGRESSIVE NRN PACIFIC
SYSTEM UPSTREAM ENERGIES APPROACH/UNDERCUT THE ALEUTIANS NEXT
WEEKEND TO LIKELY EMERGE INTO THE WRN GULF OF AK IN ACTIVE FLOW
INTO NEXT WEEK.

SCHICHTEL


$$





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