Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
605 PM EST Sun Jan 31 2021
Valid 12Z Thu Feb 04 2021 - 12Z Mon Feb 08 2021
...Overview and Guidance/Uncertainty Assessment...
A rather changeable upper pattern will be loosely driven by
troughing in the Bering Sea and ridging over the northeastern
Pacific that will, at times, poke into the mainland. The models
and even ensembles have shifted early in the period (Tue-Wed) with
the flow off Asia as well as to the south of the Aleutians. This
had a downstream affect to increase the southerly extent of
troughing south of 50N around Fri as well as a more northerly
extent of mid-latitude energy along 160W (previously forecast to
stay south of 50N). Net result is a more developed/phased system
lifting out of the mid-latitudes Fri into the eastern Aleutians
and perhaps Bristol Bay (GEFS/CMCE consensus) or just east of the
AKPen (ECMWF/ECMWF ensembles). This could then be enough to erode
the upper ridge enough over the Gulf to allow lower heights to
invade from the northeast (NW Canada) next weekend into Mon 8 Feb.
GFS/GEFS were most aggressive with this scenario while the
Canadian/ECMWF and their ensembles were farther northeast over
Banks Island or the Beaufort Sea. Finally, flow over the western
Pacific into the Bering and/or Aleutians remains quite uncertain
with little predictability. Thus, weighed heavily on the ensemble
means after a general deterministic blend Thu. This included
majority ECMWF/Canadian ensembles and minority GEFS ensembles.
...Weather/Hazards Highlights...
Precipitation will focus around the central to eastern Aleutians
as the low pressure lifts northward Friday, spreading light to
modest snow and some coastal rain to southwestern areas of the
mainland eastward across coastal Southcentral and into the
Panhandle late Fri into Sat. Warm front may bring enhanced
rain/snow to southeastern areas per the guidance, but this varies
in space and time. Ensembles focus around Yakutat but encompass
anywhere from PWC to the southern Panhandle. Another system may
spread more rain/snow to the Aleutians next weekend and into the
Gulf next Monday. Temperatures will be near to above normal over
the southwestern half of the state and near to below normal over
the northern/northeastern portions as well as over the Panhandle.
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
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