Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
749 PM EDT Mon Mar 28 2022
Valid 12Z Fri Apr 01 2022 - 12Z Tue Apr 05 2022
...Overview...
Latest forecast guidance for late this week into early next week
provides a combination of continuity and adjustments, along with
some lingering uncertainty for a potentially strong system
tracking along the Aleutians into the Gulf of Alaska. The
majority solution cluster still depicts a tightly wound system
near the Alaska Peninsula as of early Friday with arriving North
Pacific energy helping to pull low pressure southeastward before
dissipating, followed by a strong system tracking along the
Aleutians into the Gulf during the weekend into early next week.
There are still ongoing trends and meaningful spread for details
of this latter system. Based on the most likely scenario, the
combination of these systems would lead to multiple days of
precipitation from the Aleutians through the southern coast and
Panhandle. Farther north, the northwestward retreat of an upper
high over the Arctic should allow some shortwave energy to
retrograde across the northern mainland and into the northern
Bering Sea. Expect the mainland to stay in a persistent gradient
between surface high pressure over the Arctic and low pressure to
the south.
...Guidance/Predictability Assessment...
From late week into the weekend an average of the 12Z
GFS/ECMWF/CMC provided the best overall cluster to serve as the
basis for the forecast, with reasonable support from the ensemble
means for the depiction of initial low pressure over/south of the
Alaska Peninsula and the upstream system expected to track along
the Aleutians. The leading system is still sensitive to small
scale details that tend to have lower predictability a few days
out in time. Recent UKMET runs have been on the eastern side of
the envelope for this system. The primary trend with the
potential Aleutians system is for faster progression of the main
low (a nod to recent ECMWF runs), with this low ultimately
reaching the Gulf of Alaska--in contrast to the parent low hanging
back over the Bering Sea while a leading frontal wave reaches the
Gulf. Although there has been decent clustering with fairly
incremental trends among the means and majority of models, there
has almost always been at least one very different solution to
cast some doubt on the consensus. Lately it has been UKMET runs
which have depicted a fast and southward extreme, and now the 18Z
GFS (as did isolated GFS runs in prior days) shows a similar idea.
Thus confidence in a specific solution is lower than would
typically be the case for a system of its size and ensemble mean
agreement/continuity.
After early Sunday, the recent trends away from the slower side of
the spread for the Aleutians system recommended replacing the CMC
component of the blend with the 12Z GEFS/00Z ECMWF means to
maintain a coherent evolution for low pressure tracking into the
Gulf of Alaska. Consensus suggests this system should shear out
after early next Tuesday.
Aside from the specifics there is reasonable continuity from
yesterday for the idea of energy retrograding across the northern
mainland during the first half of the period. While the
similarity of the 12Z GFS/ECMWF both eventually having an upper
low reaching the northern Bering Sea may be mere coincidence,
preference was to keep a significant operational model weight
through late in the period to maintain reasonable detail for low
pressure to the south. Upper flow over the mainland may become
fairly ill-defined by late in the period.
...Weather/Hazard Highlights...
Heaviest precipitation and strongest winds with the system
forecast to be near the Alaska Peninsula as of early Friday should
occur before the start of the extended forecast period. Some
rain/snow should linger over the area into Friday while fronts
associated with this system and an immediately trailing feature
will likely produce precipitation of varying intensity along the
southern coast and Panhandle. A strong upstream system should
track along the Aleutians and into the Gulf of Alaska, producing
organized precipitation and brisk to strong winds. However there
is still meaningful uncertainty with specifics of this system, and
precise effects along the Aleutians and into areas near the Gulf
will be very sensitive to the system's track/strength. Also of
note, the gradient south of Arctic high pressure may support a
period of strong winds across the North Slope.
Above normal temperatures should be most common over the
southwestern half of the mainland, with greatest anomalies being
for morning lows over far southwestern areas late this week into
the weekend. The northeastern half of the mainland should see a
mix of above/below normal readings, with below normal temperatures
most likely over the North Slope and central-northeast interior.
The general transition of the mean pattern toward lower heights
aloft may lead to a gradual cooling trend over some areas, in
particular expanding the coverage of below normal highs. Expect
the Panhandle to see below normal highs and near to above normal
lows through the period.
Rausch
Hazards:
- Heavy precipitation across portions of mainland Alaska, Thu, Mar
31.
- High winds across portions of mainland Alaska, Thu, Mar 31.
- High winds across portions of mainland Alaska, Thu-Sat, Mar
31-Apr 2.
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