Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
532 PM EST Sat Nov 21 2020
Valid 12Z Wed Nov 25 2020 - 12Z Sun Nov 29 2020
...Continued stormy pattern next week...
...Overview and Guidance/Predictability Assessment...
Progressive and amplified flow will maintain the barrage of storms
across parts of Alaska next week into next weekend. 12Z
models/ensembles were in decent agreement for the first few days
of the period, with expected track/depth/timing differences. Trend
has been toward a slightly slower/deeper depiction of the systems
but has remained rather steady considering the speed of the jet
(~150kts later next week south of the Aleutians). Utilized a
mostly deterministic blend of the 12Z GFS/ECMWF/Canadian/UKMET
Wed-Fri before trending toward about a 50% ensemble mean blend by
next weekend. The Fri-Sat system showed some spread mostly in the
N-S direction (ECMWF farthest south, Canadian to the north, GFS
more or less in the middle) but still preferred to keep the low
north of the Aleutians through the southern Bering into Bristol
Bay by 12Z next Sat. Front should move into the Gulf then
Panhandle later next weekend per the consensus/ensembles.
...Weather/Threats Highlights...
Lead system along western Alaska/Y-K Delta/AKPen will spread
modest to perhaps locally heavy precipitation along Kodiak across
the southern Kenai Peninsula as the frontal boundary moves
eastward. Triple point will take aim on the northern Panhandle
where precipitation should maximize around Yakutat before
spreading down the Panhandle as the warm front comes ashore and
weakens. Next system in the Bering Fri-Sat will spread
rain/snow/wind across the Aleutians to southwestern Alaska as the
parent low may slowly decay over Bristol Bay to the AKPen.
Precipitation distribution is uncertain as the models differ on
the amount of forcing over water vs land and moisture influx.
Southern to southeastern-facing areas would be favored as is
typical for this evolution. This includes the western side of Cook
Inlet and southeastern Kenai, where several inches of
precipitation are possible. Temperatures will remain well above
normal along northern areas thanks to upper ridging and above
normal lower level temperatures, extending along
western/southwestern areas as well. Southeastern portion of the
mainland into the Panhandle will see varied temperatures within
several degrees of typical late November values.
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