Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
625 PM EST Tue Jan 19 2021
Valid 12Z Sat Jan 23 2021 - 12Z Wed Jan 27 2021
...Overview and Guidance/Uncertainty Assessment...
Upper ridging over the northeastern Pacific on Saturday will
transition westward and southwestward next week, favoring
troughing in the Bering Sea. Several shortwaves will be blocked
over the Mainland and split either toward the Bering Strait and/or
into the Gulf. The models/ensembles showed reasonable agreement to
start the period this weekend, but then diverged in
timing/amplitude.
Lead system will sink southeastward Saturday out of the Gulf as
the first Bering system moves northeastward past the Dateline by
Sunday. Blend of the 12Z GFS/ECMWF/UKMET offered a good starting
point. Thereafter, the guidance split between a quicker and slower
cluster. The quicker models included the GFS/Canadian and most
GEFS/CMC ensembles. The slower camp included the 12Z ECMWF/UKMET
and most ECMWF ensembles. The slower camp was preferred due to the
fairly strong, though transient, ridging downstream Monday over
the Gulf as well as upstream over the western Pacific. Continuity
was on the slower rather than quicker side as well. However,
utilized the 00Z ECMWF ensemble mean fully by later in the period
as it was not as slow as the 12Z ECMWF. This would slow the system
on Sunday in the Bering and allow for a surface wave to develop
but eventually split to the southeast as it system tries to
maneuver through the upper ridge in weakened fashion around next
Tue. Next Bering system would move into the central part of the
Sea by next Wed per the ECMWF ensemble mean (and actually the 12Z
GEFS mean as well).
...Weather/Hazards Highlights...
Gulf system on Sat will bring light to modest precipitation to
areas of the Panhandle and far southeastern Alaska as it slips
southeastward. Bering system on Sunday will bring breezy
conditions and light to modest precipitation to the Aleutians,
enhanced around the wave along the front where precipitation could
be heavy (more than one inch). This could spread along the western
coast of Alaska as the front pivots and redevelops to the
southeast, across the AKPen, late Mon into Tue. Next system could
spread additional rain/snow to the Aleutians Tue-Wed next week,
along with windy conditions as the guidance shows potential for a
modestly deep system.
The majority of the state will see above to much above normal
temperatures this weekend, with the most extreme anomalies likely
to be over northern and western areas. Temperatures should cool
back toward more typical late January values next week. The
Panhandle may see a larger area of below normal readings after the
weekend system departs and offshore flow increases.
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
No significant hazards are expected over Alaska during this
forecast period.
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