Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
544 PM EST Wed Jan 01 2020
Valid 12Z Sun Jan 05 2020 - 12Z Thu Jan 09 2020
A persistent upper-level mean trough centered across the interior
of Alaska is forecast by most guidance to continue through the
extended forecast period, ensuring a continued period of well
below-average temperatures. Between the trough/upper low across
Alaska and a building ridge across the north central Pacific, an
active storm track should persist from northeast Asia, near/south
of the Aleutians, and into the Gulf of Alaska. The ECMWF/CMC were
the solutions most closely clustered with the ensemble consensus
during days 4-5 (Sun-Mon) with a low pressure system forecast to
enter/cross the Gulf of Alaska as it moves toward Southeast
Alaska. The GFS has shown run-to-run continuity issues and was not
preferred for use in a blend. Thus, a blend of the 12Z ECMWF/CMC
was heavily used during days 4-5, along with a small component of
the 00Z ECENS mean. Model spread was a bit higher with the next in
the series of low pressure systems, forecast to near the western
Aleutians by late Mon/early Tue. Models do show some consensus
that this could be quite deep, with even the ensemble means
showing a low into the 970s by early Tue, but solutions differ on
the track of what appears to be a rather complex and chaotic
evolution, potentially featuring at least a couple areas of low
pressure. Farther north across the Interior and the North Slope,
the ECMWF/CMC and ensemble means showed general consensus that
upper troughing should remain in place, while the GFS attempts to
bring an upper high from the Arctic Ocean southward into Alaska
where it interacts with shortwave ridging in the Gulf to develop a
weak ridge axis across Alaska. The GFS solution was not preferred
here either, and WPC favored the idea shown by the ECMWF/CMC of
keeping the Arctic and North Pacific streams more separate, as the
upper trough over the Interior and the intense cold air at the
lower levels should be somewhat difficult to expel. Thus, the
forecast during days 6-8 (Tue-Thu) made use of gradually
increasing and majority ECENS ensemble mean, along with
diminishing use of the ECMWF/CMC through time.
This pattern should result in a continuation of well below average
temperatures across much of mainland Alaska, with max and min
temperatures, especially across the Interior as well as
southwestern portions of mainland Alaska as much as 20-30 deg F
below average. The active storm track from the Aleutians into the
Gulf of Alaska should keep chances for precipitation fairly high
from extreme southeastern portions of mainland Alaska into the
Panhandle/Southeast Alaska, as well as across the Aleutians,
through the extended forecast period.
Ryan
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:
- Much below normal temperatures across portions of mainland
Alaska, Sat-Wed, Jan 4-Jan 8.
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