Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
657 PM EST Tue Feb 06 2024
Valid 12Z Sat Feb 10 2024 - 12Z Wed Feb 14 2024
...Overview...
From the weekend into next week, the best clustering of guidance
shows a steadily building/amplifying upper ridge from the Alaska
Panhandle/western Canada into the mainland while a broad cyclonic
circulation with potentially multiple upper lows should prevail
from the Aleutians/Bering Sea through Kamchatka. Behind a strong
short-term system likely to be near the southeastern coast of the
mainland by the start of the period early Saturday, dynamics
embedded within North Pacific flow should generate some surface
systems that could initially track toward the southern coast. The
storm track should transition more northward into the Aleutians as
the downstream upper ridge builds. System specifics have low
confidence at this time but the most likely pattern evolution
should favor southerly to southeasterly low level winds and best
precipitation emphasis directed at the southern coast.
...Guidance Evaluation/Preferences...
In relative terms the most confident aspect of the forecast
continues to be with the building upper ridge over the
Panhandle/western Canada and extending increasingly northwestward
with time. Thus far the GEFS/ECens means have been remarkably
agreeable and consistent with this ridge through day 8 Wednesday,
both in terms of alignment/position and strength. There is still
the occasional stray solutions that eventually close off a high
center, such as the 12Z ECMWF or 00Z GFS. The new 18Z GFS closes
off a high but to the east of the Panhandle, leading to a
consensus ridge position overall. The latest ECMWF-initialized
machine learning models favor an open ridge like the means and
operational model majority. There is also some spread for
westward extent of the upper ridge which affects surface low
track/timing but has low predictability at this time.
While the upper ridge is still fairly flat during the weekend, the
operational models show a general signal for one or more fairly
small-scale North Pacific systems to track into a broad range
between the Alaska Peninsula and Gulf of Alaska. However
continuity and agreement have been very poor in recent operational
model runs and ensemble spread is great enough for the means to
show no well defined waves. Thus preference favors a conservative
blend approach reflecting a modest leading feature.
Farther west there is an indication of a potentially strong system
reaching near the Aleutians by the Sunday-Tuesday time frame but
again poor agreement/continuity for details. The 12Z
ECMWF/CMC/UKMET all bring the strong storm to the Aleutians by
early Monday (12Z CMCens mean even a little farther north). In
contrast the 06Z/12Z GFS and 00Z ECMWF as well as 12Z GEFS/00Z
ECens are farther south at that time. Thereafter, the operational
models generally continue to track the system northward into the
Bering Sea at their respective speeds--depending on upper ridge
details to the north/northeast--while the ensemble means dampen
out this system in deference to another system to the south of the
Aleutians. Latest machine learning models are all over the place
for North Pacific through Bering Sea details as well, highlighting
the uncertainty of the forecast. A blended preference
incorporates the range of guidance, bringing a parent low to the
Aleutians with a triple point wave that consolidates with the low
to the north, followed by some northward progression. The new 12Z
ECens mean (arriving after forecast preparation) sort of fits into
this template before again dampening the Aleutians system in favor
of another low farther south.
Low pressure expected to reach near the southwestern coast of the
mainland by early Saturday exhibits some spread for its ultimate
track as well, but the spread still yields a similar pattern
overall with some degree of low pressure lifting northward along
the western coast into Monday while an axis of low pressure
lingers to the southwest.
Guidance comparisons led to a starting blend consisting of the 12Z
ECMWF, GFS, and UKMET/CMC in order from more to less weight early
in the period. Detail divergence in 00Z/12Z ECMWF runs by
mid-late period favored splitting ECMWF input between the two runs
from day 6 Monday onward while adding in 20-40 percent of the 12Z
GEFS/00Z ECens means by days 7-8 Tuesday-Wednesday. The blend
maintained some 12Z GFS and a little CMC at that time.
...Weather/Hazards Highlights...
Southerly low level flow and one or more compact surface waves
should focus coastal rain and inland/higher elevation snow along
most of the southern coast and Panhandle during the weekend. Some
of this precipitation may be heavy, adding to the heavy
precipitation forecast along and near the Kenai Peninsula on
Friday (before the start of the extended period, and focused ahead
of the system reaching the southwestern mainland by early
Saturday). As upper ridging likely builds with time and the storm
track should shift westward, expect the best precipitation focus
to shift somewhat westward as well by the early-middle part of
next week--most likely the Alaska Peninsula with some leeway to
the west or east. Low level winds over the Northeast
Pacific/Alaska Peninsula should trend southeasterly while their
strength will depend on how deeply individual storm systems
develop. Some lighter precipitation may extend farther north over
the mainland, with a drier trend over the east. In general the
pattern should promote above normal temperatures over most
locations with highest anomalies over the west and north. Some
pockets of near to slightly below normal readings will be possible
over the eastern mainland and Panhandle.
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