Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
546 PM EDT Wed Sep 02 2020
Valid 12Z Sun Sep 06 2020 - 12Z Thu Sep 10 2020
...Heavy rain early next week over much of the coast...
Robust system out of the central Pacific will bring heavy rain and
windy conditions to the Alaska Peninsula eastward across
Kodiak/Kenai toward the Panhandle early next week. Rainfall
amounts could be 5-10 inches over the first few days of the period
with higher local amounts in favored areas but lower amounts in
shadowed areas. Main parent low will lift northward along or just
off the west coast (eastern Bering) into the Seward Peninsula with
another swath of locally modest/heavy rain. Models and ensembles
continue to cluster near the ensemble means, and a
blended/consensus solution of the latest 12Z guidance served as a
good starting point. UKMET became notably quicker with the system
by Tue as it moves NNE then NE over far NW Alaska, and was
discounted. However, overall trend was a bit quicker but not to
that extent. Slowly moving cold front in meridional flow will pump
ample moisture into the region up and over the Alaska Range as a
warm front jumps northward. Milder air will surge northward as
well, but will be replaced by a bit cooler air behind the front.
For next Wed/Thu, another system out of the western Bering will
dip near the western Aleutians, but the models remained spread
out. Trended toward the ECMWF ensemble mean which was closer to
continuity than the GEFS mean and tends to perform better in
amplified flow. Upstream extratropical transition of Typhoons
Maysak and Haishen will likely lead to a strong ridge/trough
couplet over eastern Asia/Bering around the middle of next week.
Too early to tell if this may lead to another surge of moisture
from the mid-latitudes/sub-tropics.
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, Sun-Tue, Sep 6-Sep 8.
- Heavy rain across portions of mainland Alaska, Sun-Mon, Sep
6-Sep 7.
- 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