Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
801 PM EDT Wed Oct 13 2021
Valid 12Z Mon Oct 18 2021 - 12Z Fri Oct 22 2021
...Stormy Pattern Continues from the Aleutians through Southern
and Southeast Alaska...
... Guidance and Predictability Assessment...
Model guidance continues to have above average predictability with
the evolution of multiple waves crossing the Bering Sea into the
Gulf of Alaska. This pattern will be favorable for stormy
conditions for much of the southern parts of the state through the
extended period. The latest runs of the ensemble means are now
closer to the ECWMF and CMC solutions and overall are in pretty
good agreement. The WPC Alaskan medium range product suite used
the deterministic models (GFS/ECMWF/UKMET/CMC) blended with the
GEFS and ECENS ensemble means. More deterministic weighting was
given during the early periods with higher predictability, with
more weighting towards the ensembles by the end of the period to
smooth out the differences.
...Pattern Overview and Weather/Hazard Highlights...
The mean low pressure pattern over the Aleutians and Gulf will
keep cloudy/unsettled conditions through the extended period. In
addition, the daily temperatures are expected to remain below
normal. Temperatures across the northern and central parts of the
state will be closer to normal with a period of slightly above
normal temps by early next week as weak upper level ridging builds
in from the east.
Gusty winds along with scattered to widespread precipitation is
expected across the Aleutians, southern and southeast portions of
the state through early next week. The initial low pressure system
will be tracking into the Gulf of Alaska will keep increased cloud
cover, gusty winds and an enhanced precipitation pattern for
southern and southeast Alaska. There will be periods where
moderate to locally heavy rain is expected for the Panhandle, with
snow likely in the higher elevations of southern Alaska.
Upstream flow is then expected to drive a deep storm into the
Bering Sea by next weekend with downstream energy transfer
allowing for triple point low developments, which should work
across the eastern/central Aleutians and the AK Pen region and
eventually into the Gulf of Alaska by next Monday. The Aleutians
will get another round of heavy rainfall and gusty winds this
weekend, shifting to the southern coast/Alaskan Panhandle by early
next week. The exact amounts, along with how far inland the
precipitation shield extends, will be dependent on the position of
the low as it enters the Gulf. This is one of the features that
has spread in the guidance so specifics are less confident.
Campbell
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
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon-Wed, Oct 18-Oct 20.
- Heavy precipitation across portions of mainland Alaska, Sun, Oct
17.
- High winds across portions of mainland Alaska and the Aleutians,
Sat-Sun, Oct 16-Oct 17.
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