Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
748 PM EDT Wed Mar 11 2020
Valid 12Z Sun Mar 15 2020 - 12Z Thu Mar 19 2020
...Overview and Guidance/Predictability Assessment...
The forecast period begins on Sunday with an impressive upper
level ridge and surface high anchored over the northern Gulf of
Alaska, with 500mb heights approaching 576 dm. A storm system
just south of the central Aleutians is forecast to weaken and then
evolve into an open wave by Tuesday as it slowly lifts northward
towards the western Alaska mainland. This will also serve to
weaken the pronounced ridge over the Gulf some and shunt the ridge
axis southward. Around the same time, a disturbance is progged to
track eastward just north of the Arctic Coast, with the CMC and
ECMWF tracking closest to the coast.
There will be two noteworthy storm systems that will likely affect
the Bering Sea region and the western Aleutians, with the first
storm expected to affect mainly eastern Siberia and then weaken as
it passes well to the northwest of the Alaska mainland. The
second and potentially more impactful storm may impinge on the
western Aleutians by early Wednesday and then reach the Bering by
Wednesday night and into Thursday. Given that the GFS and ECMWF
are indicating surface pressures near 970 mb and the CMC even
stronger, along with good ensemble support, it is reasonable to
expect that this will be the next major storm system to eventually
affect the Alaska domain. The deterministic guidance has improved
with the position of the storm, and the ECMWF is a little south of
the model consensus.
...Weather Highlights/Threats...
Western Alaska appears to be most favored for above normal
precipitation for this time period as moisture advects northward
around the western side of the large high pressure ridge, with
several inches of snow likely for northwest portions of the state
this weekend. Much of the eastern half of the state, and
extending to the Panhandle region, should be mainly dry during
this time. The other story will be the well above normal
temperatures across inland sections of the state owing to the
strong upper level ridge in place.
Hamrick
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
Hazards:
- Heavy snow across portions of northwest mainland Alaska, Wed,
Mar 18.
- Much above normal temperatures across portions of northern
mainland Alaska, Sat-Wed, Mar 14-Mar 18.
- Much below normal temperatures across portions of southeast
mainland Alaska, Sat, Mar 14.
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