Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
612 PM EST Mon Mar 08 2021
Valid 12Z Fri Mar 12 2021 - 12Z Tue Mar 16 2021
...Overview and Guidance/Uncertainty Assessment...
Progressive quasi-zonal flow in the mid- and higher latitudes will
trend toward increased troughing in the Bering Sea, downstream of
elongated upper ridging from eastern Asia (China/Mongolia) into
the western Pacific Ocean between 35-45N. Coupled with increasing
ridging over the Canadian Archipelago, this may act to at least
temporarily slow the pattern as a couple closed systems try to
develop south of Alaska.
Lead system out of the northeastern Pacific will still be subject
to adjustments into the short range, owing to continued
differences in timing/strength of northern and southern stream
influences. Non-Canadian consensus was preferred as the Canadian
remained most aggressive with a closed low likely too far north
(~45N) compared to the ECMWF/GFS (~30N). Trailing shortwave may
help linger at least part of the front near the southern Panhandle
early Saturday.
To the west, deepening troughing will favor increased meridional
flow across the Aleutians and then into western areas of the
Mainland as a robust southern stream low lifts into the Bering Sea
late Fri into early Sat. Guidance has trended stronger with this
low compared to the in-situ surface low over the NW Bering, but
otherwise maintained the same idea as the past several days.
Trended toward an even deterministic/ensemble blend between the
GFS/ECMWF given enough agreement overall. System should break
apart, stretched in the flow, with its southern portion moving
into the Gulf and perhaps slowing as the pattern may amplify over
the Northeastern Pacific into Northwestern Canada.
...Weather/Hazards Highlights...
High pressure over the Interior Friday will drift eastward then
southeastward this weekend, supporting colder temperatures 10-20
degrees below normal from Southcentral Fri to southeastern areas
and the Panhandle by the weekend. Ahead of the Bering system,
temperatures will rise to well above normal values along western
coastal areas, perhaps 10-25 degrees (actual temperatures 10s/20s
north, 30s over southwestern areas). After the system weakens and
translates into the Gulf, cooler air will move back into western
areas.
Lingering rain/snow will exit the Panhandle Friday (timing
differences to be resolved in the short range), focusing the
precipitation mostly south of Juneau. Next system in the Bering
will bring windy conditions and some rain/snow to the islands,
enhanced around the incoming southern surface low. Milder
temperatures suggest a transition from snow to rain for some
areas. Another wave along the front is forecast to redevelop into
the Gulf, perhaps enhancing the rain/snow over the
AKPen/southwest/coastal Southcentral areas and Kodiak.
Fracasso
Hazards:
- High winds possible for the western portions of the Aleutians,
Sat, Mar 13.
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