Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
630 PM EDT Wed Jul 21 2021
Valid 12Z Sun Jul 25 2021 - 12Z Thu Jul 29 2021
...Guidance/Predictability Evaluation...
The synoptic pattern during the period is forecast to undergo a
change from the stagnant cutoff upper low in the Gulf of Alaska
(gradually filling in) to more pronounced upper troughing
developing over the Bering Sea extending into the Aleutians. This
pattern shows average to above average clustering with the latest
model guidance including the deterministic ECMWF/GFS/CMC/UKMET.
The main uncertainties lie with the potential development of
stronger surface low late in the period. The deterministic
solutions show varying scenarios but confidence is increasing that
a deeper low will approach the Bering Sea late in the period. This
could result in some unsettled weather for the Aleutians and
western mainland region but details are murky at this point. For
this cycle, the days 4-5 blend were comprised of the 12Z
ECMWF/GFS/CMC/UKMET while given the increasing model spread for
days 6-8, a heavier blend of the ECENS/GEFS was used while the
deterministic ECMWF was included as well.
...Weather/Threats Highlights...
The main precipitation and unsettled weather will be focused
across the Aleutians and western mainland throughout the period as
a series of low pressure systems impact the region. The systems
for this weekend and early next don't appear to be too significant
and hazardous at this time but late in the forecast period
(Tuesday/Wednesday next week), a potential deeper/stronger low
could drop into the Bering Sea and lead to higher waves and
heavier precipitation. Otherwise, generally below normal
temperatures are expected across the mainland through the period,
particularly in the Far North.
Taylor
Hazards:
No significant hazards are expected over Alaska during this
forecast period.
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