Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
600 PM EST Tue Feb 16 2021
Valid 12Z Sat Feb 20 2021 - 12Z Wed Feb 24 2021
...Overview and Guidance/Uncertainty Assessment...
Ensembles show upper troughing or a weak upper low swinging
through the Interior and Southcentral next week on the southwest
side of a parent/deeper upper low near the Canadian Archipelago.
As the child upper feature continues eastward into the Yukon next
Monday, the parent upper low will continue its slow march westward
through the Arctic Ocean. This will maintain cold temperatures
over the interior of the state with a storm track over the
Aleutians and across the Gulf into the Panhandle. This will lead
to bouts of modest to locally heavier rain/snow to the Panhandle
for the period, especially this weekend.
Broad consensus served as a reasonable starting point though with
uncertainty in timing of smaller-scale features in the rather
quick west-to-east flow along 55N Sat-Mon. 12Z GFS was a bit off
in timing compared to the 12Z ECMWF and ensembles, but was not
necessarily implausible. Agreement was good on the deepening of
the system into the Gulf by early Sunday as the system pushes
through the Panhandle. Thereafter, quick and weak to modest
intensity systems will fly through the Bering/Aleutians next
Mon-Wed with little predictability downstream of a fast W Pac jet.
Ensembles diverged as well with the ECMWF/Canadian ensembles
leading the slower GEFS ensembles. Given the strong jet upstream
translating eastward, relied mostly on the quicker ensembles but
with the caveat that a deeper system upstream could buckle the
flow enough to slow things down in future runs.
...Weather/Hazards Highlights...
Defined system into the Gulf (lead weaker system Saturday then the
stronger one by Sunday) will yield modest to perhaps locally heavy
rain/snow over the Panhandle followed by showery precipitation
Monday as the upper trough moves through. Next week, weaker system
in the flow will produce generally light rain/snow to the
Aleutians and into southwestern Alaska as they progress eastward.
Well below normal temperatures are likely for much of the Interior
and into Southcentral by Monday as the sub-500 dm heights rotate
through the region. The North Slope and Panhandle will see near to
below normal temperatures through the period. Some moderation is
possible over the Aleutians to southwestern Alaska by the middle
of next week as heights rise in advance of troughing in the far
western Bering Sea.
Fracasso
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle,
Sat-Mon, Feb 20-Feb 22.
- Much below normal temperatures across portions of mainland
Alaska, Sat-Tue, Feb 20-Feb 23.
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