Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
617 PM EST Tue Nov 17 2020
Valid 12Z Sat Nov 21 2020 - 12Z Wed Nov 25 2020
...Overview and Guidance/Predictability Assessment...
Active pattern across the high latitudes this weekend into next
week as an upper high near far northeastern Alaska splits WNW-ESE.
This favors continued/reinforced troughing across the Bering into
the Gulf via several systems. Lead system will translate through
the Gulf (old parent low in the Bering) early Saturday and into
the Panhandle. Next system will follow behind, astride the
Aleutians and into the Gulf by early Monday. Last system will move
into the western Bering next Tuesday and toward the AKPen around
next Wednesday. The 12Z models/ensembles were in decent agreement
to start with the first system, though the GFS/UKMET were a bit
different than the ECMWF/Canadian. Favored the ECMWF-led consensus
nearer to the ensemble means. For the 2nd system (Sun-Mon), GFS
appeared too quick given the slower trend overall, so favored the
ECMWF/Canadian/UKMET which were displaced just a bit south of the
slower ensemble means. This would keep that surface low a bit
farther off the coast, perhaps with greater affect to the
Panhandle late Monday. For the final system in the Bering next
Tuesday, models were spread in each direction so trended
completely to the ensemble means as a course of least regret. To
the north, upper ridging will give way to lower heights with time
in weak southeasterly mid-level flow.
...Weather/Threats Highlights...
Focus for heavier precipitation will lie along southern coastal
areas into the Panhandle every 1-2 days or so with each system.
Given the slightly different approaches for each system, appears
that the precipitation could be spatially spread out. First system
will bring windy conditions and heavy rain/snow to coastal
Southcentral into the Panhandle, followed by the second system
Monday that may shift that axis to the central/southern Panhandle
as the triple point may head toward Haida Gwaii. Last system may
have a less favorable moisture source connection, but still could
spread some modest rain to the Aleutians next week.
Fracasso
Hazards:
- Heavy precipitation across portions of mainland Alaska and the
Aleutians, Sat, Nov 21.
- High winds across portions of mainland Alaska and the Aleutians,
Fri-Sat, Nov 20-Nov 21.
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