Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
651 PM EST Tue Feb 23 2021
Valid 12Z Sat Feb 27 2021 - 12Z Wed Mar 03 2021
...Active Pattern from the Bering Sea/Aleutians to the
Mainland/Gulf of Alaska...
...Overview and Guidance/Uncertainty Assessment...
Upper pattern will be driven by a strong positive height anomaly
moving off Hokkaido this weekend (+3.5 sigma 500mb heights per the
ECMWF ensemble mean) will eventually translate eastward to the
western Bering Sea by the middle of next week. This will favor
downstream robust yet progressive troughing through the Bering to
the Gulf of Alaska in general west-to-east flow. With a rather
defined wavelength, the models/ensembles were in good agreement
overall except for the UKMET. There were timing differences
between the GEFS/ECMWF ensembles but a middle ground solution was
preferred absent any notable trends. This fit close to continuity
as well. Increased ensemble weighting by later in the period due
to uncertainty in smaller-scale features that may or may not
deepen (or even exist) within the flow.
...Weather/Hazards Highlights...
Mild temperatures late this week over southwestern areas will be
replaced by cooler than normal temperatures after the lead front
pushes through and heads swiftly through the Gulf/Panhandle
Saturday into early Sunday. GFS was much wetter than the ECMWF
(Canadian near the middle) but a blended solution should suffice
as the progressive pattern should limit excessive precipitation
totals, but amounts could top a couple inches (liquid) with this
system. Next system will bring another round of wind to the
Aleutians/Bering into southwestern areas late Sun through Mon then
into the Gulf around next Tue. The ECMWF was much wetter than the
GFS with that system but the Canadian was near the middle. Again,
system should be progressive to limit excessive amounts but still
1-3" (liquid) may be possible from Southeastern areas into the
Panhandle. Temperatures will trend toward normal and then below
normal over much of the state by the middle of next week as the
upper low moves through.
Fracasso
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sat-Sun, Feb 27-Feb 28.
- High winds across portions of mainland Alaska and the Aleutians,
Mon-Tue, Mar 1-Mar 2.
- High winds across portions of the Aleutians, Sun-Tue, Feb 28-Mar
2.
- Much above normal temperatures across portions of mainland
Alaska, Fri-Sat, Feb 26-Feb 27.
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