Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
642 PM EST Mon Feb 01 2021
Valid 12Z Fri Feb 05 2021 - 12Z Tue Feb 09 2021
...Overview and Guidance/Uncertainty Assessment...
Upper ridging between Siberia and the North Pole will slowly spill
over into the Canadian Archipelago, allowing a closed low
initially near Banks Island to migrate westward toward the North
Slope/Beaufort Sea. Farther south, ridging over the northeastern
Pacific/Gulf of Alaska will weaken with time, opening up the flow
along 50N out of the northern Pacific. After a sizable change in
the guidance yesterday, the models/ensembles had a better handle
on the forecast for at least the Fri-Sun period. Used a blend of
the 12Z GFS/Canadian/ECMWF and the GEFS/ECMWF ensembles which take
an initial system nearing the central/eastern Aleutians Friday
eastward atop the ridge as it collapses to the southeast. By
Sunday, GFS started to become rather aggressive with height falls
into northeastern Alaska to the southwest of the ensemble
consensus (closer to the ECMWF at least for Sunday). After Sunday,
deterministic models diverged rather quickly out of the north
central Pacific in the quasi-zonal flow ahead of a deepening upper
low off Kamchatka, suggesting a full use of the ensembles for next
Mon-Tue to mitigate errors in the timing of a system into the Gulf
around next Monday and into the Bering next Tuesday.
...Weather/Hazards Highlights...
Northerly to northeasterly track of the lead system out of the
mid-latitudes Friday will bring a modest surge of moisture into
the eastern Aleutians and along the coast of Southcentral Alaska
as it translates into the Gulf. Some locally heavy snow and
coastal rain are possible, expanding into at least the northern
Panhandle ahead of the warm front. Thereafter, precipitation will
generally be light except around the system Sun-Mon from the
Aleutians to the Gulf which may be enhanced a bit around the
surface low. Temperatures will initially be near to above average
over much of Southcentral as the system moves through. Below
normal temperatures over northeastern areas will expand
southwestward as heights lower out of northwestern Canada this
weekend. Much of the state may see below normal temperatures by
next week by about 5-15 degrees.
Fracasso
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
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Fri-Sat, Feb 5-Feb 6.
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