Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
657 PM EST Fri Jan 14 2022
Valid 12Z Tue Jan 18 2022 - 12Z Sat Jan 22 2022
...Overview...
Today's guidance generally shows an eventual transition toward a
pattern that is warmer, and across the far southern
mainland/Panhandle wetter as well, by late next week as upper
ridging becomes more prominent from near the British Columbia
coast northwest into the mainland. However there is considerable
uncertainty over some of the specifics of this trend in light of
very poor model agreement/continuity in recent days for upper flow
details over and near the mainland. Meanwhile over the North
Pacific there is a general consensus for an axis of relatively low
heights aloft and low pressure at the surface. At least a couple
individual individual features within this area will tend to
maintain breezy and somewhat unsettled conditions along the
Aleutians.
...Guidance/Uncertainty Assessment...
Operational runs of the GFS/ECMWF/CMC in the past couple days or
so have been all over the place with respect to what becomes of
upper trough/low energy currently expected to be near the
northwest coast of the mainland as of the start of the period
early Tuesday. This suggests below average confidence in any
specific solution until guidance can improve its clustering and
maintain some run-to-run continuity. Early in the period there is
a signal from latest models that some energy within the initial
feature may shear eastward while a combination of
remaining/additional energy may reinforce the trough and form
another upper low over or near the northwestern mainland. The
past two ECMWF runs and 12Z CMC (jumping well south of its 00Z
run) are most aggressive in bringing a deep upper low into the
west-central mainland. The 12Z UKMET is not quite as deep or
southeast while the 00Z/06Z/12Z GFS runs pull the energy farther
west into the Bering Sea. In contrast the ensemble means show
mere troughing over the northwestern mainland after early Tuesday.
Interestingly the ECMWF mean has been steadily trending toward
lower heights within this trough, or at least delaying how much
heights rise on the northern periphery of the upper ridge that
builds in from the southeast late in the week, while the GEFS mean
has been fairly steady with a stronger ridge extending into the
mainland. Overall preference was to start with a blend of
operational guidance (GFS represented by the 06Z run since its
overall pattern fit better with consensus than the 12Z version)
Tuesday into early Wednesday and then start incorporating 12Z
GEFS/00Z ECens input so that days 7-8 Friday-Saturday consisted of
60 percent total ensemble weight. Versus yesterday's continuity,
the resulting forecast yields a deeper trough/upper low over the
northwestern mainland into Thursday but not to the depth and
southeastward position of the ECMWF/CMC. Then the feature
retrogrades into the Bering Sea in a manner hinted at by the
means. The new 12Z ECMWF mean still shows more modest troughing
over the northwestern mainland while the 18Z GFS now shows a deep
upper low wobbling just south of the Bering Strait after
midweek--somewhat east of where the prior GFS runs positioned
their features.
The aforementioned blend provides reasonable continuity for a
system that may track toward or south of the Alaska Peninsula and
possibly into or near the Gulf of Alaska around
Wednesday-Thursday. GFS/CMC runs show the farthest north/west
track for the parent low, with the intermediate blend having the
support in principle from the less defined ensemble means.
Farther west, an initial system south of the Aleutians should
retrograde out of the picture after Tuesday while another system
tracking south of it reaches closer to the Aleutians late in the
week. There is still quite a bit of spread for specifics of the
latter system, favoring the model/mean blend approach.
...Weather/Hazard Highlights...
Depending on specifics of the leading North Pacific system, some
moisture may reach the Alaska Peninsula already by Tuesday or so.
With somewhat less sensitivity to details there should be an
increase of precipitation across the southern coast and Panhandle
by late in the week as the associated front reaches the area and
then flow ahead of an upstream Pacific system brings additional
moisture into the region. Amounts could be moderate to heavy over
some areas while wind speeds may pick up as well. Elsewhere,
portions of the Interior may see light snow in the vicinity of a
front draped across the area while North Pacific systems will
produce periods of brisk to strong winds and some precipitation
along the Aleutians.
Currently expect the North Slope and Seward Peninsula to see below
normal temperatures for most of the period while above normal
readings prevail farther south. In general anomalies for min
temperatures should be somewhat warmer than those for max
readings. Most areas should see a noticeable warming trend toward
Friday or Saturday with the best potential for highest anomalies
over Southcentral. The forecast over parts of the central/western
mainland is uncertain, with potential for colder readings if the
deeper and southeastward side of the guidance spread for the upper
trough/low over the northwestern mainland ends up gaining more
credibility.
Rausch
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Fri, Jan 21.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Fri, Jan 21.
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