Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
628 PM EDT Fri Jul 23 2021
Valid 12Z Tue Jul 27 2021 - 12Z Sat Jul 31 2021
...Guidance/Predictability Evaluation...
A stagnant cutoff low in the Gulf of Alaska will weaken but
meander in the region through much of the extended range period.
This should allow for upper level ridging to build into the
eastern part of the mainland. Meanwhile, a deep upper low will
move into eastern Russia as heights lower across the Bering Sea
and eventually the Aleutians. After day 5, the guidance continues
to show significant uncertainty regarding the Bering Sea trough
and smaller scale pieces of energy which may undercut the trough
and move over or south of the Aleutians. Given the uncertainty,
the WPC forecast trended quickly towards the ensemble means days
5-7, with some minor contribution from the 12z GFS which was the
deterministic solution closest to the means.
...Weather/Threats Highlights...
The main areas of precipitation and unsettled weather will be
focused across the western and northwestern mainland throughout
the period as southerly flow ahead of the Bering Sea trough
interacts with a cold front and stalled stationary boundary across
the northern Mainland. The best chance for heavier precipitation
will be Tuesday and Wednesday across parts of the Seward
Peninsula, and northward. Moderate to locally heavy rains may
continue after Wednesday, but confidence in the amounts and
particular locations remains low at this time. High waves and
gusty winds may also present themselves for the west coast
mainland. Troughing extending into the Bering Sea and Aleutians
later in the week could lead to some higher waves and
precipitation for parts of the Aleutians into next weekend. For
western and northern parts of Alaska, temperatures should remain
below normal, but should trend warmer for eastern parts of the
state as upper level ridging builds in aloft.
Santorelli
Hazards:
- Heavy rain across portions of mainland Alaska, Tue-Wed, Jul
27-Jul 28.
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