Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
558 PM EDT Tue Oct 13 2020
Valid 12Z Sat Oct 17 2020 - 12Z Wed Oct 21 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
model/ensemble families, with the GEFS cluster offset from the
ECMWF/ECMWF ensembles, and in turn the Canadian/Canadian
ensembles. There was enough overlap of the 12z Canadian with the
00-12z ECMWF and 00z ECMWF Ensemble Mean to blend these solutions
days 4-6.
With growing differences in timing on Days 7-6, I omitted the 12z
Canadian global to avoid depicting a low spread over the large
area. So the Days 7-8 forecast was a blend of 00-12z ECMWF and
00z ECMWF Ensemble Mean. The continuing differences with offshore
surface systems keeps forecast confidence low in the Aleutians to
northern Pacific.
...Weather/Threats Highlights..
With the approach of the upper trough, western Alaska to the upper
Aleutians/AK peninsula look to be showery Sat. Residual
showers are over coastal southern Ak to the panhandle Sun.
Moderate to locally heavy showers are expected.
The next significant precip event awaits the development of a
cyclone from a north Pacific wave midweek. The 00-12z ECMWF show
rain developing in the upper Aleutians/possibly the AK peninsula
Tue- 20 Oct- Wed 21 Oct.
Initial below temperatures near the Ak/Yukon border late this week
retreat and transition so much of Alaska is above normal through
the weekend into early 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:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sun-Tue, Oct 18-Oct 20.
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