Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
746 PM EDT Tue Sep 15 2020
Valid 12Z Sat Sep 19 2020 - 12Z Wed Sep 23 2020
...Overview and Guidance/Predictability Assessment...
The mean pattern will generally be troughy for much of the Alaska
region during the extended periods, especially between 160W and
170W, with multiple waves moving through. The first lifts
northeast into Canada on Friday, while the next quickly dives from
the Bering Sea, across the Aleutians and into the Gulf this
weekend. The third system deepens, becoming well-defined and
wrapped up as it tracks toward/over the Aleutians mid-to-late in
the forecast period. Stronger winds and additional focused rain
will accompany this system. High winds may impacts part of Kodiak
Island and areas to the west and south Monday and Tuesday. Heavy
precipitation spanning Unimak Island to Glacier Bay also possible
early next week.
While there is some spread in timing and strength, there was been
decent consensus the last few runs. Continue to prefer a blend of
12Z ECWMF/GFS/CMC for most periods- with a little inclusion of of
the 12Z UKMET initially for the evolution of the leading system
and introduced light weighting of the 00Z EC ensemble and 12Z GEFS
mean Monday and Tuesday.
...Weather/Threats Highlights...
Showers are expected across the southern coastal area with some
local enhancement after the lead low pressure system passes
through. A majority of the Interior will have daily temperatures
near average, or above, for mid-September. However, the clouds and
showers will keep much of the southern coastal areas below
average, as well as, portions of the North Slope. Another round of
rainfall is expected to pass over the Aleutians and into the
Alaska Peninsula by late this weekend through midweek as a
deepening, low tracks toward the Aleutians.
Campbell
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, Fri, Sep 18.
- Heavy precipitation across portions of mainland Alaska and the
Aleutians, Mon-Tue, Sep 21-Sep 22.
- Heavy rain across portions of the Alaska Panhandle, Sun, Sep 20
and Tue, Sep 22.
- High winds across portions of mainland Alaska, Mon-Tue, Sep
21-Sep 22.
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