Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
759 PM EDT Tue Mar 10 2020
Valid 12Z Sat Mar 14 2020 - 12Z Wed Mar 18 2020
...Overview and Guidance/Predictability Assessment...
The forecast period begins on Saturday with an impressive upper
level ridge and surface high anchored over the northern Gulf of
Alaska, and should persist through the weekend. A storm system
south of the central Aleutians will begin to erode the ridge some
by early next week with the greatest height anomalies shunted
southward, and the models are still have difficulty resolving the
eventual track and evolution of that surface low and thus its
impacts on the Aleutians. The 12Z UKMET was a northern outlier by
Day 4 and did not appear to be a plausible solution, so it was not
incorporated into the forecast. This is noted to a lesser degree
with the 18Z GFS, and the ensemble means support a solution closer
to the CMC and ECMWF that are more suppressed and eventual evolve
into an open wave.
By Tuesday the models are indicating the potential for a strong
low pressure system to approach the western Aleutians and
potentially affect the Bering Sea region by Wednesday. Given that
the GFS, ECMWF, and CMC all indicate sub-970 mb lows by 12Z
Wednesday, 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 main uncertainties exist with
latitudinal placement, with the CMC south of the GFS/ECMWF and the
ensemble means, and the GFS and ECMWF somewhat slower than the
ensemble means. There will also be a weaker storm tracking north
of the Arctic Coast early next week, with the latest GFS
suggesting a more northward trajectory and the CMC more
progressive.
...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 central and eastern Interior, and
extending to the Panhandle region, should be mainly dry during
this time. The other story will be the 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,
Fri-Sat, Mar 13-Mar 14.
- Much above normal temperatures across portions of northern
mainland Alaska, Fri-Tue, Mar 13-Mar 17.
- Much above normal temperatures across portions of central
mainland Alaska, Sat-Tue, Mar 14-Mar 17.
- Much below normal temperatures across portions of the Alaska
Panhandle and mainland Alaska, Fri-Sat, Mar 13-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