Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
510 PM EDT Thu Sep 03 2020
Valid 12Z Mon Sep 07 2020 - 12Z Fri Sep 11 2020
...Dynamic Storm Pattern for Alaska...
There is a strong guidance signal showing that amplified upper
trough development out through the Bering Sea will support storm
genesis. The deepened low will lift northward along or just off
the west coast (eastern Bering) into the Seward Peninsula early
next week and support a swath of high winds/seas and locally heavy
precipitation. Models and ensembles continue to cluster near the
ensemble means, and a blended/consensus solution of the compatible
12 UTC GFS/ECMWF/UKMET serves as a good forecast starting point
Monday-Wednesday. Ample moisture will pump inland to the interior
through the very heavy rain supported southern tier of the state
in deep layered southwesterly flow channeled between the storm and
an amplifying downstream upper ridge. Upstream extratropical
transition of Typhoons Maysak and Haishen over northeastern Asia
also supports strong ridge/trough couplet development and
maintenance over eastern Asia/Bering next week.
Later, there is also a less certain but emerging guidance signal
favoring additional low development into the Aleutians in about a
week in the wake of the lead storm, but it still too early to tell
given guidance forecast spread if this may lead to another surge
of deep moisture from the mid-latitudes/sub-tropics. An ECMWF
ensemble mean solution, along with some manual adjustments to
insure a deepened low consistent with favorable upper troughing,
seems to provide max WPC continuity and offer the threat
potential.
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
Hazards:
- Heavy precipitation across portions of mainland Alaska, Sun-Mon,
Sep 6-Sep 7.
- Heavy rain for parts of the Alaska Panhandle and mainland
Alaska, Sun-Wed, Sep 6-Sep 9.
- High winds across portions of mainland Alaska, Sun-Mon, Sep
6-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