Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
623 PM EDT Mon Aug 2 2021
Valid 12Z Fri Aug 6 2021 - 12Z Tue Aug 10 2021
...Overview and Guidance/Predictability Evaluation...
An amplified and blocky ridge in place over mainland Alaska is
forecast to slowly break down around the end of this week as a
pattern change evolves during the medium range forecast period.
The weakening ridge will then allow for troughing associated with
a deep upper level low across the Bering Sea to drive a cold front
across western Alaska. The Bering Sea low will meander across the
region through most of the forecast period, while a couple of
shortwaves/surface lows rotate around the base of the trough into
the Aleutians. In terms of the model guidance, there remains
above average agreement among the deterministic runs through about
day 6, and then the CMC diverges somewhat and becomes faster with
upper level height falls associated with the Bering Sea trough
compared to the model consensus. The WPC forecast was based on a
general deterministic model blend through Sunday, and then less of
the CMC and more of the EC and GEFS means for early next week.
...Weather/Threats Highlights...
Widespread showers are expected across western Alaska late this
week as moisture surges northward ahead of the Bering Sea upper
low. Going into the weekend, the moisture should begin
overspreading the southern half of the state as a cold front moves
inland. Periods of showers will continue to affect the Aleutians
through next weekend associated with a couple of weaker embedded
surface lows pivoting around the main upper level gyre over the
Bering Sea.
Temperatures across the state should be above average for most of
the region underneath the upper level ridge. As the ridge begins
to decay and troughing moves into the state by Friday,
temperatures should quickly trend cooler into the weekend and
early next week. Most of the North Slope region should be below
normal as a shortwave drops southward from the Arctic Ocean.
Hamrick
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
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