Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
655 PM EST Wed Jan 03 2024
Valid 12Z Sun Jan 07 2024 - 12Z Thu Jan 11 2024
...Stormy conditions for the Aleutians and western Alaska into the
weekend...
...Overview...
An active pattern is in store for the extended period as strong
low pressure systems track from the North Pacific into the
Aleutians and Bering Sea. This track will be upstream from fairly
persistent Arctic ridging aloft while an eastern Pacific mean
ridge should let a couple shortwaves pass through the northeastern
Pacific with associated waves/frontal systems. The leading low and
associated fronts will usher in a broad area of strong winds,
including parts of the mainland, during the weekend while details
are more uncertain for a potential second system by next
Tuesday-Wednesday. This pattern will likely produce highest
totals of precipitation from the Alaska Peninsula to the Kenai
Peninsula.
...Guidance Evaluation/Preferences...
The past few runs of guidance have been persistent with keeping a
mean trough over the Aleutians/North pacific/Beaufort Sea with
multiple lows tracking through while ridging is in place
downstream and extending into the Arctic Ocean. However, the model
spread with the details have not resolved especially
beyond the strong storm reaching the Aleutians and Bering Sea
during the weekend. The lowest central pressure for the leading
low around Sunday still ranges between the upper 940s and 950s mb
while the ensemble means are expectedly weaker but still in the
upper 950s mb. The spread widens to around 15 mb by mid-week and
beyond for the next low lifting into the region.
The past ECMWF runs have been closest to the middle of the spread,
between the slightly weaker/northward CMC and southward GFS.
There is reasonable agreement that the storm's leading front
should be weakening as it reaches the Gulf of Alaska and offshore
the Panhandle by early Monday. However due to shortwave evolution
sensitivity, guidance has been more diverse and erratic with a
small-scale North Pacific wave which may reach near the Alaska
Peninsula by Monday.
Toward the end of the period next Tuesday-Wednesday there is a
decent signal for upper ridging to rebuild into the northeastern
Pacific and portions of the mainland, but with a fair amount of
spread for details of low pressure to the west. GEFS/ECens mean
continuity has been in favor of another system tracking through
the Aleutians and into the Bering Sea (with latest GFS/CMC runs
falling into this cluster). A couple ECMWF runs were suppressed
and progressive with low pressure, a scenario not reflected in
other guidance. The preference was to maintain a more northward
progression into Wednesday but acknowledging the emerging
potential for a slower trend. As a result heights were rising
across the eastern two-thirds of the Mainland.
The WPC model composite maintained a sense of continuity by
utilizing an initial blend of the ECWMF/GFS/UKMET/CMC for about
the first half of the period then quickly included ensemble means.
...Weather/Hazards Highlights...
Before the start of the period, expect high winds across the
Arctic Coast/North Slope region to persist into Friday and lead to
periods of ground blizzard conditions. Then during the weekend the
deep storm tracking northward through the Aleutians and Bering Sea
will spread a broad area of high winds across those areas as well
as portions of the mainland. Strongest winds over the mainland
should be over parts of the Seward Peninsula and Lower Yukon/Lower
Kuskokwim regions, with blizzard conditions possible there as
well. The combination of the storm's leading front and a potential
trailing wave/front will spread precipitation across and east from
the Aleutians, with the most pronounced focus likely to be along
the Alaska Peninsula and Kenai Peninsula during Saturday-Sunday.
Meaningful totals may also be possible a little farther inland
over the far southwestern mainland. What moisture reaches the
southeast coast/Panhandle will produce much lighter precipitation,
while fairly dry conditions should prevail over the Interior and
North Slope. By next Tuesday-Wednesday another storm system may
bring precipitation and brisk to strong winds to at least the
Aleutians if not the Bering Sea and far western mainland as well.
Monitor forecasts as details for this latter system become better
resolved.
Most of the state will see above to well above normal temperatures
through the period, with highest anomalies likely over northern
and western parts of the mainland. The primary exception will be
over the eastern Interior, where negative anomalies should
moderate after the weekend, and over the central-southern
Panhandle with moderately below normal temperatures.
Campbell/Rausch
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