Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
316 PM EDT Fri Apr 27 2018

Valid 12Z Tue May 01 2018 - 12Z Sat May 05 2018

...Guidance and Predictability Assessment...

Alaskan/WPC coordination led to preference for a composite blend
of the 12 UTC GFS/GEFS and 00 UTC ECMWF ensemble mean. Guidance
was not well clustered in a active pattern with above normal days
4-8 forecast spread/uncertainty due to embedded system emphasis
and timing differences, especially compared to the plausible but
outlier 00/12 UTC ECMWF runs. WPC continuity was reasonably
maintained with this blend process.


...Pattern Highlights/Threats...


An active pattern is anticipated for Alaska and vicinity next week
that will include two main storm tracks. Early week low/frontal
system progression from the Bering Sea will support an active
weather focus/precipitation swath inland across western and
southwestern AK into the interior and North Slope overtop an
additional northern Gulf of Alaska system split that will provide
modestly unsettled flow into srn/sern AK.

Northern Pacific storm development upstream may subsequently
support a potentially deep low track into/south of the Aleutians
Wednesday-Saturday that also threatens maritime interests with
heavy seas/winds. Guidance has trended farther south with this low.

WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html

Schichtel