Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
555 PM EDT Wed Oct 14 2020
Valid 12Z Sun Oct 18 2020 - 12Z Thu Oct 22 2020
...Guidance/Predictability Assessment...
The models indicate the upper trough moves slowly east from the
Bering Sea and to the west coast of Alaska over the weekend,
reloading in the Bering Sea next week. The models are in good
agreement into the weekend over northern to central Alaska, with
differences developing centered over the northern Pacific and the
adjacent Aleutians.
The timing and phasing of individual waves varies by models/ model
runs, with the 12z GFS initially in good agreement with other
models/meas through about day 4.5, and then the GFS holds on to
the anticyclone in southern AK longer than other solutions, and
is slower in moving the storm north towards the Aleutians.
The cross check with the GEFS Mean show the operational GFS to be
an outlier, with the 500 mb pattern in the GEFS more closely
resembling the Canadian and ECMWF Ensemble means Mon and Tue 20
Oct.
Manual progs blended the 00-12z ECMWF and 00z ECMWF Ensemble
Mean,as the 12z Canadian cyclone track was offset to the west
in the north Pacific to the Aleutians days 6-7. Better agreement
develops by day 8 as the occluded low moves more slowly in the
southern Bering Sea.
The next shortwave 500 mb trough rotating south of this cyclone
across the north Pacific should spawn the next cyclone development
in the middle to latter portions of next week.
...Weather/Threats Highlights..
With the approach of the upper trough, western Alaska to the upper
Aleutians/AK peninsula/Kodiak Island look to be showery Sat-Sun.
The next significant precip event awaits the arrival of the north
Pacific wave midweek in the Aleutians. The 00-12z ECMWF show rain
becoming widespread in the upper Aleutians/possibly the AK
peninsula Tue- 20 Oct- Wed 21 Oct. Locally heavy rain is possible.
Initial below temperatures near the Ak/Yukon border late this week
persist into early next week. Much of western Alaska is above
normal through the weekend into the middle of next week.
Petersen
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
Hazards:
None forecast.
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