Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
754 PM EDT Fri Oct 22 2021
Valid 12Z Tue Oct 26 2021 - 12Z Sat Oct 30 2021
...Overview and Guidance/Predictability Assessment...
Model spread does not appear excessive today near the Alaskan
landmass. However, toward the latter part of next week, the ECMWF
and GFS are completely out of phase near and west of the
Aleutians. The ECMWF and EC mean are more compatible with
yesterday's forecasts, as a low pressure system/wave riding
through the top of the subtropical high in lower latitudes is
forecast to head northeastward toward the Gulf of Alaska next
weekend. The CMC mean agrees with the ECMWF solutions in the broad
sense. The GFS, on the other hand, keeps a strong high pressure
system in place south of the Aleutians when a large low pressure
system is forecast to approach the western Aleutians during the
latter part of next week--a scenario in stark contradiction to the
ECMWF and WPC continuity.
Therefore, the WPC medium-range forecast grids for Alaska begin
with an even blend of the 12Z GFS & GEFS, the 12Z ECMWF/12Z EC
mean, together with smaller contributions from the 12Z CMC/CMC
mean. The blend is then quickly weighed toward the ECMWF
solutions by Day 5 and then progressively trended toward the EC
ensemble mean beyond Day 5, together with relatively small
percentages from the GEFS mean and the CMC mean.
...Weather/Hazard Highlights...
The medium-range period should begin with a frontal wave
developing over the northern portion of the Bering Sea next
Tuesday. As the frontal wave tracks eastward, precipitation
should increase somewhat from the eastern Aleutians to
southwestern mainland Wednesday into early Thursday together with
gusty winds. Meanwhile, generally quiet conditions are expected
for much of mainland Alaska, with occasional snow showers along
the North Slope and the Arctic Coastal Plain. The southern coast
and Panhandle should see a modest increase of rain/snow through
midweek as a broad cyclonic circulation with surface troughs is
forecast to meander over the Gulf of Alaska.
Expect above normal temperatures to dominate much of interior
Alaska to start the medium-range period next Tuesday. A slow
cooling trend is anticipated for the entire area as heights aloft
are forecast to slowly decline due to the slow approach of the
broad cyclonic circulation over the Gulf. This will lead to
progressively colder readings along the southern periphery of
mainland Alaska and into the Alaska Panhandle for the medium-range
period and into next weekend.
Kong
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
- No significant hazards are expected over Alaska during this
forecast period.
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