Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
606 PM EST Sun Mar 07 2021
Valid 12Z Thu Mar 11 2021 - 12Z Mon Mar 15 2021
...Overview and Guidance/Uncertainty Assessment...
Progressive quasi-zonal flow will trend toward increased troughing
in the Bering Sea, downstream of elongated upper ridging from
eastern Asia (China/Mongolia) into the western Pacific Ocean. Lead
system out of the northeastern Pacific remains tough to pin down
details, owing to continued differences in timing/strength of
northern and southern stream influences. After a
quicker/less-phased shift yesterday, consensus drifted back toward
a bit slower but still not quite robust system. ECMWF ensembles
remained slowest along with the Canadian, hanging back a deep
upper low well south of the Gulf. Again favored the 12Z ECMWF with
some influence from the GFS and then GFS parallel as the
operational version was quickest. This stayed toward the middle of
the spread as a continued hedge against future model shifts.
To the west, deepening troughing will favor increased meridional
flow across the Aleutians and then into western areas of the
Mainland as a system congeals from northern and southern streams
into a stretched frontal system with the parent low well northwest
over northeastern Russia. With differences in the evolution (speed
of southern system into the in-situ front), opted to rely on the
rather agreeable ensemble means (ECMWF EPS and GEFS mean).
Amplifying trough/ridge pattern may slow the system into western
Alaska and the Gulf next weekend/early next week, but downstream
ridging does not look that impressive just yet.
...Weather/Hazards Highlights...
High pressure over northwestern areas will slowly move through the
Interior and Southcentral Thu-Sat, supporting colder temperatures
10-15 degrees below normal. The colder temperatures will make its
way southeastward as the surface high slips into northwestern
Canada/Yukon.
Lead Gulf system will track toward the central/southern Panhandle,
focusing the precipitation there as the front moves into British
Columbia late Fri. Heaviest amounts per the in-house
bias-corrected ensemble QPF should stay south of Juneau. Next
system in the Bering will bring windy conditions and some
rain/snow to the islands as the parent low stays well to the
northwest. Milder temperatures will precede the Bering system on
southerly flow from west to east next weekend, suggesting a
transition to rain for some areas. Wave along the front is
forecast to redevelop into the Gulf, perhaps enhancing the
rain/snow over the AKPen/southwest areas into Kodiak.
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