Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
601 PM EDT Mon Mar 29 2021
Valid 12Z Fri Apr 02 2021 - 12Z Tue Apr 06 2021
...Guidance/Uncertainty Assessment...
The 12 UTC GFS/ECMWF solutions seem reasonably clustered and have
decent ensemble support into day 4/Friday. Model solutions diverge
quickly after that, still due to upstream sensitivities in both
the amplitude evolution and stream interaction without a clear
signal for any singular solution. Accordingly, a 12 UTC GFS/ECMWF
and GEFS/ECMWF ensemble mean composite was used as a basis for the
day 4/Friday forecast before quickly transitioning to a 50-50
composite of the GEFS/ECMWF ensemble means days 5-8 (Saturday-next
Tuesday). The ensemble means are decently compatible considering
the rapidly increasing forecast spread and maintain better WPC
continuity than the models.
...Weather/Hazards Highlights...
Lingering upper trough support over the Interior may favor
unsettled and cooled weather to include some locally enhanced
snows Friday. Meanwhile to the south, an amplified upper trough
dug over the eastern Gulf of Alaska will support a lingering
precipitation focus into the Panhandle.
Upstream, an unsettling northern Bering Sea system Friday will
progress into the mainland by the weekend. This should support
some threat of enhanced snows from western and southwestern Alaska
into the central mainland. There is additional but uncertain
western Bering Sea system potential by early next week that could
effect the Aleutians. These system energies may tend to dig to the
lee of a mean upper ridge built up through the Aleutians. This
pattern may favor periodic reinforcement of surface lows from the
northern to eastern Gulf of Alaska that would offer a recurring
threat for lead flow to fuel periods of moderate terrain enhancing
precipitation for southeast Alaska.
Schichtel
Hazards:
- Heavy snow across portions of mainland Alaska, Fri-Sat, Apr
2-Apr 3.
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