Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
641 PM EDT Sat Aug 01 2020
Valid 12Z Wed Aug 05 2020 - 12Z Sun Aug 09 2020
...A Stormy Pattern for Alaska...
...Guidance Evaluation...
The WPC Alaskan medium range product suite was primarily derived
from a composite blend of now well clustered guidance from the 12
UTC GFS/ECMWF/Canadian and the 19 UTC National Blend of Models
days 4-8. Convergence of these guidance pieces toward a more
common solution bolsters forecast confidence for this period, but
growing forecast spread day 7/8 suggests continued uncertainty
with smaller scale system specifics. This solution reasonably good
WPC continuity.
...Weather Highlights/Threats and Predictability...
A deepened surface low under a supporting closed upper low/trough
over the Northern Gulf of Alaska into midweek will fill over the
eastern Gulf into Thursday. Wrapping moisture and rain into
southern/southeast Alaska will also presents a maritime hazard
over the Gulf of Alaska.
Upstream, guidance has really come together compared over the past
two days in depiction of a deep surface low and closed upper
low/trough to develop and work into the Southern Bering
Sea/Aleutians by midweek. This powerful low will progress into
Bristol Bay, Southwest/Western Alaska and the Alaskan Peninsula
into Thursday, then fill into the Interior over the next few days.
Ample energy will meanwhile transfer downstream into unsettled
northern Gulf of Alaska waters next Friday into next weekend. This
system offers potential for enhanced wind/waves and rains along
the broad track, then downstream into southern/southeast Alaska.
There also seems to be an emerging guidance signal in the models
to develop a third low that may develop just to the south of the
Aleutians into Friday then downstream into the northern Gulf of
Alaska over the weekend. There is substantial uncertainty with
this system, but given lead storm track trends it seems
widespread rain, wind and waves may present yet again.
Schichtel
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