Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
703 PM EDT Mon Oct 11 2021
Valid 12Z Fri Oct 15 2021 - 12Z Tue Oct 19 2021
...Stormy Pattern Continues from the Aleutians through Southern
and Southeast Alaska...
... Guidance and Predictability Assessment...
The latest models and ensemble guidance over Alaska continues to
show above average agreement on the synoptic pattern as multiple
low pressure systems moving from the Bering Sea into the Gulf of
Alaska continue a stormy pattern. Models exhibit some timing and
detail variability, but nothing atypical for these time ranges.
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. This approach maintains good continuity with
yesterdays WPC forecast.
...Pattern Overview and Weather/Hazard Highlights...
An energetic and progressive flow aloft will support multiple
surface low pressure systems affecting portions of Alaska late
this week and into early next week. The first low will be moving
into the Gulf by the beginning of the period, offering a continued
favorable moisture and enhanced precipitation pattern for southern
and southeast Alaska. Moderate to locally heavy rainfall is
possible across portions of the Panhandle region, 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 AKPen region and
eventually into the Gulf of Alaska by next Monday. This should
again bring a coastal and maritime threat for heavy rainfall and
gusty winds to the Aleutians this weekend and the southern
coast/Alaskan Panhandle by early next week. There remains some
differences in exact placement of this low as it gets into the
Gulf, which of course would impact precipitation amounts along the
coast and also how far inland the precipitation shield extends.
Mean low pressure and cloudy/unsettled conditions across the Gulf
and southern Alaska region through the period should keep
temperatures below normal. Across northern and central Alaska,
temperatures should 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.
Santorelli
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:
- High winds across portions of mainland Alaska and the Aleutians,
Sat-Sun, Oct 16-Oct 17.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon, Oct 18.
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