Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
652 PM EST Tue Mar 08 2022
Valid 12Z Sat Mar 12 2022 - 12Z Wed Mar 16 2022
...Overview...
Latest guidance maintains the idea that a strong shortwave
rounding the top of a Siberia upper ridge during the weekend will
drop southward into the mainland early next week, leading to a
northeast-southwest oriented upper trough. This feature and
possibly additional energy arriving from the northeast may
ultimately lead to an embedded upper low reaching near the
southern coast/southwestern mainland by the middle of next week.
Farther south and within fairly active Pacific flow, a strong
mid-latitude system should weaken somewhat as it approaches the
Panhandle early next week. At the same time a trailing system
will likely track just south of the Aleutians, but with some
uncertainty over what interaction may occur between it and initial
low pressure/upper dynamics lingering over the Aleutians. Some
details of these Pacific systems will depend on exactly how the
upper trough over the mainland evolves.
...Guidance/Predictability Assessment...
Deeper ensemble mean trends for the developing mainland upper
trough early next week, most noticeable starting with the daytime
runs from Monday, are adding support to the recent operational
model consensus that has been showing a rather deep trough. The
primary forecast considerations are that the 12Z and new 18Z GFS
runs ultimately pull the embedded upper low farther southwest than
most other guidance (leading to a greater westward extent of
precipitation along the southern coast late in the period) and the
UKMET being a little slow with the arriving feature through the
end of its run early Monday. The 06Z GFS compared much better to
the model/mean majority through the period. At the moment the
latest ensemble means and ECMWF/CMC/06Z GFS are quite similar by
day 8 Wednesday in showing an upper low around the far southwest
corner of the mainland.
Regarding Pacific systems, there are still important
track/evolution differences for the leading low tracking toward
the Panhandle early next week. The past couple ECMWF runs have
been on the southern side of the spread at that time but the 12Z
run did at least trend north of its previous run. Remaining
models and means show a somewhat farther north track and/or
northward elongation or redevelopment in response to the
amplifying mainland upper trough. Meanwhile guidance has been
inconsistent with some details of the system tracking south of the
Aleutians, partially due to uncertainty over how much interaction
may occur with residual dynamics/low pressure over or near the
Aleutians. The 12Z ECMWF is somewhat on the northern side of the
spread. By late in the period the ensemble means agree that the
primary focus for low pressure should eventually gravitate to the
northeastern Pacific/Gulf of Alaska due to the mainland upper
trough.
Guidance comparisons led to starting the first half of the
forecast with the 06Z GFS and 12Z ECMWF/CMC/UKMET, with least
weight on the UKMET. Mixing in 30 percent total weight of the 12Z
GEFS/00Z ECMWF means for days 7-8 Tuesday-Wednesday provided a
reasonable balance of accounting for increasing detail
uncertainties while reflecting recently increasing support for a
mainland trough tilted somewhat more to an operational model
consensus.
...Weather/Hazard Highlights...
The primary precipitation focus during the period should be along
the southern coast and Panhandle. Initial light to locally
moderate activity will likely trend gradually lighter and more
scattered during the weekend. Then expect low pressure tracking
toward the Panhandle by Monday to increase precipitation over at
least parts of the region, with moisture possibly expanding back
along the southern coast depending on how the mainland upper
trough evolves. Current forecast preference would lead to less
westward extent along the southern coast than indicated by the
12Z/18Z GFS runs. Another system reaching the Northeast
Pacific/Gulf of Alaska may enhance precipitation around Wednesday.
It will take additional time to resolve the finer details of
precipitation coverage and intensity during Monday-Wednesday. The
Aleutians may see periods of mostly light precipitation and there
is still uncertainty over the effects of low pressure forecast to
track to the south early in the week. Guidance consensus shows
brisk to strong northerly winds spreading across the Bering Sea
and Aleutians by Tuesday-Wednesday.
During the weekend, above normal temperatures will prevail over
the southern mainland and North Slope with below normal readings
(especially for highs) in-between and over the eastern mainland.
The upper trough settling into the mainland by early next week
should promote a colder trend with expanding coverage of below
normal anomalies. Some pockets of above normal readings could
linger over the North Slope and for min temperatures in the far
south. Expect most of the Panhandle to see below normal highs
through the period and a mix of above or below normal lows.
Rausch
No significant hazards are expected over Alaska during this
forecast period.
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