Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
405 PM EDT Sun Oct 06 2019
Valid 12Z Thu Oct 10 2019 - 12Z Mon Oct 14 2019
Models and ensembles show an amplified but progressive pattern in
place across Alaska and vicinity for the extended period. Guidance
consensus was good into day 5/Fri, though the larger scale flow
evolution even seems fairly well depicted by most guidance through
day 8. Smaller scale systems after day 5 continue to offer plenty
of timing variance, but there was fairly good agreement with the
ensemble means (ECENS/GEFS) days 6-8. Accordingly, WPCs Alaska
medium range suite for today was primarily derived from a blend of
the ECMWF/GFS and respective ensemble means, with majority
deterministic weighting in the early days (4-5) and increasing
mean blend through the end of the period.
This brings a shortwave/possible closed low into the Gulf of
Alaska on Thursday, eventually weakening as it moves into western
Canada next weekend. This system includes some remnant tropical
moisture from what was Typhoon Mitag, so enhanced precipitation
(locally heavy) can be expected along with a continued maritime
risk. Behind this, there remains decent model signal for the
development of another organized shortwave trough to track across
the Aleutians Fri, into the Gulf by Saturday. This should also
feed additional precipitation chances across southern and
southeast Alaska.
By early next week, most guidance suggests a deep low pressure
system drops into the northern Bering Sea, though plenty of
timing/placement/amplitude differences remain at this time scale.
Regardless though, this could present a maritime risk (high winds,
heavy seas) across the Bering Sea and potentially along parts of
the Aleutians and western coast of mainland Alaska. This system
may also spread increased precipitation into parts of mainland
Alaska, though impact/amounts remains highly uncertain.
Santorelli
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html