Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
529 PM EST Fri Nov 20 2020
Valid 12Z Tue Nov 24 2020 - 12Z Sat Nov 28 2020
...Continued stormy pattern next week...
...Overview and Guidance/Predictability Assessment...
Energetic Pacific flow will keep the parade of systems coming into
Alaska from the southwest through next week. 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 the GFS idea from 24 hrs ago with a more defined southern
system across the Aleutians Tue into the eastern Bering/Bristol
Bay (from along the front attached to the parent low in the NW
Bering). With support from all models and ensemble means, depicted
this as a modest ~970mb low 12Z Wed. That will move into the
Gulf/Panhandle as previously forecast as the pattern remains
progressive. Trailing systems have been trending toward being more
defined as well, with a potentially quick-hitting but strong
system around next Friday. Given that just 24 hrs ago there was
little support for more than a weak/modest cold front, opted to
rely on a model/ensemble blend and take this astride the Aleutians
into Bristol Bay next Sat, with the caveat that this will likely
shift in details. Deterministic models later next week
(GFS/ECMWF/Canadian) represented plausible solutions but
confidence will increase if/when we see persistence in the
guidance.
...Weather/Threats Highlights...
Each system in the pattern will spread light to moderate
precipitation over much of the state except for northern and
northeastern areas on the edge of upper ridging. Focus for most of
the precipitation will be along western areas Tue/Wed as the lead
Bering system wanes, followed by southwestern areas (AKPen/Y-K
Delta) as the southern low wraps up in Bristol Bay at the same
time. Eastward movement across the Gulf should largely spare
Southcentral from significant precipitation and instead bring most
of it to the Panhandle with little break. Depending on the details
of the system next Fri, heavy precip and windy conditions could
again overspread the eastern Aleutians to the AKPen and Y-K Delta
region should the forecast unfold as depicted. Temperatures will
remain well above normal along northern areas thanks to upper
ridging and above normal lower level temperatures, perhaps
extending along western areas as well. Southeastern third of the
mainland into the Panhandle will see varied temperatures with
several degrees of typical late November values.
Fracasso
Hazards:
- Heavy precipitation across portions of mainland Alaska, Wed, Nov
25.
- Heavy precipitation across portions of the Alaska Panhandle,
Mon, Nov 23 and Thu, Nov 26.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Mon-Tue, Nov 23-Nov 24.
- High significant wave heights for coastal portions of the Alaska
Panhandle and mainland Alaska, Mon, Nov 23.
- High significant wave heights for coastal portions of the Alaska
Panhandle, Tue, Nov 24.
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