Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
541 PM EDT Tue Sep 01 2020
Valid 12Z Sat Sep 05 2020 - 12Z Wed Sep 09 2020
...Heavy rain possible from Kodiak across Southcentral next week...
Amplified pattern across the Pacific into/through North America
will be aided by the extratropical transitions of Typhoon Maysak
(forecast to move north through N/S Korea tomorrow 9/2) and
Tropical Storm Haishen (forecast to also move into the Korean
peninsula around 9/6). Models and ensembles continue to show
meridional flow into SW Alaska early next week as a well-defined
system moves across the Aleutians into the eastern Bering and NW
Alaska. The 12Z deterministic models mostly surround the ensemble
means (GEFS and ECMWF EPS) through Sunday, and a blended solution
worked well to start. GFS runs and the ECMWF were still a but
farther east than the Canadian/UKMET with the lead system Sat/Sun
toward Kodiak or the AKPEN into Bristol Bay. Ensembles were split
but perhaps had a few more members carry a weakening low just east
of Kodiak. Regardless, this will dissipate in advance of the more
substantial system Sun/Mon that will bring in additional rain/wind
to the eastern Aleutians through Southcentral. Locally heavy rain
is possible in favored south/southeastward-facing locations. An
additional area of at least modest rain will be over the western
coastline near the track of the surface low. Milder air will lift
northward before being shunted eastward as the cold front slowly
advances eastward.
By next Mon-Wed, warm front will continue northward as the parent
low skirts the west coast toward the Seward Peninsula, eventually
translating eastward up and over the upper ridge over the Gulf.
Back to the west, models/ensembles show additional troughing
digging through the western Bering, but at different latitudes.
Split the difference for now as upstream extratropical transition
will no doubt play a role in the flow orientation/strength.
Fracasso
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 rain across portions of the Alaska Panhandle and mainland
Alaska, Sat-Mon, Sep 5-Sep 7.
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