Gale Warning 6, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
540 AM AKST Fri Jan 5 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Sunday)...

A weak surface trough and upper level wave continue to lift north
over the coastal mountains this morning. These features are
producing snow showers from the eastern Kenai Peninsula east to
Cordova. Rain is mixing in at times at lower elevations, around
Whittier and Cordova. While shower activity is expected to
diminish through the day as the trough and upper level wave both
weaken, an additional 3 to 6 inches of snow is possible from
Turnagain Pass to Moose Pass with 1 to 2 inches possible for
lower elevations such as Seward. A moderately strong southeasterly
flow will continue across the coast mountains this morning,
keeping most of the shower activity confined to the coast.
However, a few showers may develop across Cook Inlet, the
Anchorage Bowl, and the Mat-Su Valleys later today as the flow
weakens. A few isolated showers will remain over the coastal
mountains into Saturday; however, a transient ridge moving
overhead will limit the extent and amount of precipitation with
any showers.

The break will not be long for Kodiak nor the Southcentral
Coastline as a new frontal boundary will extend from the low in
the southern Bering across into the Gulf of Alaska. This front
will sweep northward similarly to the last boundary, reaching
Kodiak Island first by late Saturday morning. For Kodiak City,
precipitation will likely begin as rain, with a transition
possible to a rain/snow mix by Saturday night. For mainland
Southcentral, an initial push of light snowfall will begin across
the southern and eastern sides of the Kenai Peninsula by late
Saturday morning. On the western side of Kenai Peninsula, Homer
and Seldovia will see a similar onset time of snowfall, with
higher accumulation rates expected on the southern side of
Kachemak Bay. Persistent snowfall is expected to continue into
Sunday where the axis of moisture aligns with the flow into
Western Prince William Sound, increasing snowfall potential in
that area. This system does seem to have the potential to linger
significant snow showers across this area into the beginning of
next week. Just the period from Saturday afternoon to Sunday
evening, the higher elevations along western Prince William Sound
may see one to two feet of new snowfall. Further down during this
period, Seward and Whitter may see an additional 1-4 inches of
accumulation with 2-6 inches possible along the Turnagain Pass
corridor. It is currently unclear how much snow makes it through
the downslope hole and enters Anchorage. As the axis aligns with
Turnagain Arm by early Sunday afternoon, this seems like the best
time for some light Anchorage snowfall, however confidence is
currently not high.

-CL/TM

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3/Today through Sunday)...

The forecast remains largely on track. The biggest update with the
overnight package has been to shift the timing and track of a
powerful storm system that will impact Southwest Alaska/Bering
Sea/Aleutian Islands from tonight through Sunday. A High Wind
Watch remains in effect for the Eastern and Central Aleutians,
while a Winter Storm Watch remains in effect for the Kuskokwim
Delta coast and Nunivak Island. While some uncertainties remain,
forecast confidence is steadily increasing, and it's likely that a
decision on whether to upgrade these watches will be made with
the afternoon package.

Here's a quick recap of the synoptics, drawn mostly from the
previous forecast discussion: A 975 mb vertically stacked low near
Bristol Bay will dissipate as it heads inland through today.
Shortwaves associated with this low will bring widespread showers
(mostly snow), leading to light accumulations before precipitation
tapers off Friday night. There will be a brief break in winds and
precipitation behind the low. However, attention will quickly
shift to a rapidly deepening low over the North Pacific. The set-
up looks quite impressive, with interaction of the Polar and
Subtropical jets leading to initial intensification of a low
crossing the North Pacific; a low position between the left exit
region and right entrance region of two jet streaks; and the low
bottoming out in the 940s as it crosses the central Aleutians
tonight/early Saturday. This last point is a key contrast with the
previous system, which bottomed out over the North Pacific and
tracked into the Bering Sea as a fully occluded, vertically
stacked, weakening low. Thus, generally expect stronger winds with
this next storm system and much warmer air to stream northward
out ahead of it. The storm will lift northward across the Bering
Sea and very slowly weaken Saturday through Sunday night. It will
be much like the wake of the current storm, with showers and gusty
winds lingering across the region, but diminishing with time.

- KC/SEB

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

Most of the active weather for the long term forecast period will
take place along the western portion of the state. A longwave
Bering low persists through the early portion of the week,
allowing for precipitation to occur along the frontal boundary as
it extends into central Alaska. Southcentral and western Alaska
will have near or just below freezing temperatures early week, so
mixed precipitation is possible. Some gale-force winds will be
possible as the system moves northward. The trough associated with
the Bering low will generate a couple of shortwave lows that have
the potential of providing precipitation to southcentral Alaska
in the form of snow and a rain/snow mix.

Late Tuesday into Wednesday, a building ridge will begin to
settle into central Alaska, as the main Bering low is forced
northward, providing calmer weather for that portion of the state.
There is some inconsistency with the placement of the ridge, but
most of central Alaska is expected to be covered through the end
of the forecast period. There is model agreement that a new low
pressure system will deepen as it makes its way across the western
Aleutian Islands into the Bering Tuesday- Wednesday, but the
track of the storm relative to the western Alaska coast will be
dependent on the strength of the central Alaska ridge. Strong
gale-force winds with storm-force gusts are possible as the system
traverses the Aleutian chain.

BS

&&

.AVIATION...

PANC...VFR conditions and light northeast winds less than 10 kts
will generally persist. Southeast winds aloft will still have some
chance to produce borderline LLWS until they diminish by early
this afternoon. However, winds above the surface have thus far
remained lower than most model projections have indicated, and
have not been strong enough to produce a shear layer at/below 2000
ft. A few light snow showers could make it into the terminal
later this afternoon and evening as drying southeasterly flow
begins to weaken. This could lead to some brief reductions to MVFR
conditions later this afternoon and evening with passing showers.

-AS

&&