Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
612 PM EDT Tue Mar 23 2021
Valid 12Z Sat Mar 27 2021 - 12Z Wed Mar 31 2021
...Powerhouse weekend Bering Sea low to slam into the Alaskan
mainland into early next week...
...Guidance/Uncertainty Assessment...
Model and ensemble solutions are better clustered today days 4-8,
bolstering forecast confidence in a stormy pattern. There are
still system differences to mitigate at mid-smaller scales with
usage of a composite solution of the 12 UTC
GFS/ECMWF/UKMET/Canadian and the 19 UTC National Blend of Models
(NBM) along with some manual adjustments days 4-6
(Saturday-Monday). The 12 UTC GFS/ECMWF/Canadian, the 12 UTC
GEFS/ECMWF ensemble means and the 19 UTC NBM were used for days
7/8 (next Tuesday/Wednesday) in a period with gradually growing
forecast spread. This methodology also maintains good WPC
continuity.
...Weather/Hazards Highlights...
A moderating Bering Sea lead system with still favorable upper
support will work over the interior into the weekend and support
periods of locally enhanced snows and unsettled conditions. Ample
downstream energy transference will increasingly focus weekend
storminess over the northern then northeastern Gulf of Alaska to
support a threat for terrain focusing heavy precipitation into
Southeast Alaska before exiting the region.
Upstream, a powerhouse low is expected to emerge back into the
Bering Sea over the weekend and provide a significant maritime and
Aleutians threat. The storm is expected to reach/spread highly
unsettled conditions in earnest over the mainland then Gulf of
Alaska later weekend through early-mid next week. This would
include a substantial threat for enhanced wrapping precipitation
and high winds/waves. This has a strong guidance signal to be a
major storm.
Schichtel
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Fri-Sat, Mar 26-Mar 27.
- High winds across portions of mainland Alaska and the Aleutians,
Sun-Mon, Mar 28-Mar 29.
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards 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