Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
557 PM EDT Sat Apr 25 2020
Valid 12Z Wed Apr 29 2020 - 12Z Sun May 03 2020
...Guidance/Predictability Assessment...
Upper pattern across Alaska during the extended forecast period
shows ridging near the Bering Strait slowly migrating toward the
North Slope as a trough splits a piece off southward into
Southcentral Wednesday into Thursday. Additional troughing out of
the Bering is forecast to move east-southeastward by next weekend
with a defined system south of the Gulf. The 12Z GFS/ECMWF (and
UKMET through Friday) showed relatively good consensus with the
ensemble means during the period, and a blend of these solutions
was used as a forecast starting point.
Aleutian system on Wed will split to the southeast as its old
parent low weakens through the week. That system to the south is
forecast to lift back toward the southern Panhandle by next
weekend but the main low may stay offshore. Upper pattern would
prevent much northern movement as the upper high shows no signs of
budging by then. Over the Interior, models have wavered on how
strong an upper trough may dive into Southcentral which would
bring another shot of cooler air all the way to the Gulf. 12Z
guidance somewhat splits this trough, allowing a portion (perhaps
the majority) to run eastward into Canada with only weaker
troughing sinking to the Gulf. Ensembles have yet to form a
consensus or a defined trend as the shape/orientation of the
forcing upper high is uncertain.
...Weather/Threats Highlights...
Pattern remains rather unsettled for the Panhandle with lingering
rain/snow Wed-Thu as an old parent low weakens in the Gulf. System
next weekend to the south would bring in at least some
precipitation near/ahead of the occlusion with the heavier
rain/snow likely being forced into British Columbia but perhaps
into the southern Panhandle, too. The Interior, by contrast, will
be much nearly precipitation-free owing to the upper and sfc high.
The Aleutians will see generally lighter rain after Wednesday as
the sfc low slowly weakens. After a cooler than normal period at
the start of the week over most of the mainland, temperatures will
moderate back to within several degrees of normal for most of the
state with the better chance of sustained above average
temperatures near the Bering Sea near the upper ridge axis.
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