Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
740 PM EDT Sat Sep 04 2021
Valid 12Z Wed Sep 08 2021 - 12Z Sun Sep 12 2021
...Pattern Overview and Model Guidance...
The latest suite of model and ensemble guidance continues to show
very good agreement on the overall large scale synoptic pattern
through much of the Alaska extended range period which features a
broad upper level low which should drift south and eastward into
the Bering Sea by the latter part of next week. This should send a
couple of low pressure systems south of the Aleutians and into the
Gulf of Alaska, Wed-Fri, and again by Sat-Sun. With the first one,
which could become a fairly deep cyclone (several solutions
suggesting a central pressure as low 980mb), the deterministic
guidance has shown better agreement compared to previous days on
this, but some uncertainty remains on exact placement of the low,
the details of which should get ironed out as we get closer in
time. The 12z ECMWF was displaced north of the best consensus and
closer to the southern AK coast, which would obviously have
stronger weather hazard impacts for the southern coast into the
Panhandle region. At this time, WPC preferred a more southerly
solution, closer to the 12z GFS and CMC, which also fit well with
the ensemble means and previous WPC continuity. The next shortwave
moves into the region next weekend but the deterministic guidance
shows bigger timing and strength issues. There is good agreement
in placement with the ensemble means, but obviously in a much
weaker state. The WPC forecast for days 7 and 8 leaned more
heavily on the ensemble means, while still maintaining some modest
percentages of the ECMWF and GFS just for a little bit of added
system definition.
...Sensible Weather...
A wet pattern will remain through next week across the Panhandle
region as one system exits into western Canada on Wednesday and
the next one moves into the Gulf. Moderate to locally heavy
rainfall is likely from this main low Thursday and Friday not only
across the Panhandle, but also along parts of the southern and
southeast mainland coast. A track closer to the coast could mean
greater impacts so there's plenty of uncertainty regarding exact
locations and timing of heaviest precipitation. Regardless though,
many models suggest a modestly deep surface low which likely will
bring marine hazards and gusty winds to coastal locations as well
later next week. A cold front pushing through western Alaska will
likely bring some enhanced precipitation as well, especially for
terrain areas, with some precipitation in the form of snow. With
general southerly moist flow, cloudy conditions are likely through
the period over much of the state. High temperatures should trend
cooler through the week as the upper low becomes established over
the Bering Sea, but morning lows should remain above normal across
almost all of Alaska, with the warmest anomalies across the
northern half of the mainland.
Santorelli
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
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