Storm Warning 181, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKST Thu Dec 19 2024

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

A storm force low is centered south of Kodiak Island this
afternoon. Gusty winds and heavy rain for the Island will quickly
diminish this evening as the low tracks across the Alaska
Peninsula into the eastern Bering Sea tonight. Its front swings
up along the north Gulf coast, bringing light to moderate
precipitation to Seward and the Kenai Mountains through Friday
morning with gradually rising snow levels as warmer air moves in
from the Gulf. Precipitation for eastern Prince William Sound
will pick up overnight as a trailing shortwave moves over the
area. For the interior and population centers, light northerly
winds will pick up from the Matanuska Valley down through Homer,
but little to no precipitation is expected to make it over the
mountains to the north of Ninilchik. There will then be a brief
break in the weather Friday afternoon/evening in between storms.

The next storm, currently over the North Pacific, is expected to
take a similar track to the current system, moving into the far
southern Gulf, tracking south of Kodiak, and then into Bristol
Bay. The main difference between this system and the one today
will be its overall size. The storm today is fairly compact, but
the front on Saturday's storm is expected to extend farther to
the north, bringing more widespread wind, rain and mountain snow
to the Sound. Strong winds along the Anchorage Hillside continue
to be generally unfavored due to a strong north-south pressure
gradient down the Inlet which will cause the elevated winds
moving through the Arm to sharply bend south. The only caveat to
this will be if a mountaintop inversion sets up and some stronger
winds are trapped, but for now this appears not to be the case.

Precipitation will fall mostly as rain along coastal areas,
though strong shortwaves may spill light precipitation into the
lee-side areas from Palmer south into the western Kenai
Peninsula at times. This precipitation is expected to stick close
to the mountains and diminish further to the west. Timing of
these features will dictate whether or not this falls as rain or
freezing rain. The best chances for overrunning precipitation will
be early Saturday morning with the initial arrival of the front
and again Saturday evening/night with another, messier shortwave
progged to lift across Southcentral. With the initial wave,
precipitation would be more likely to fall as freezing rain with
temperatures in the mid to upper 20s for most locations around
Cook Inlet.

Heading into Saturday, temperatures warm into the low
to mid-30s due to winds mixing in warmer air through the mountain
gaps, decreasing the likelihood of freezing rain. However, areas
that are more sheltered from the wind may continue to receive
light freezing rain. Then of course, there is the ever present
threat of rain falling on snow-covered roadways and the ice it
can generate. For Prince William Sound, Valdez also looks to be
in the freezing rain risk area as colder temperatures have the
potential to stick around Saturday morning during the initial
wave of precipitation. Unsettled weather continues into Sunday as
a series of weak shortwaves continue to lift across the Gulf and
over Southcentral Alaska.

CJ/CQ

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS
(Days 1 through 3: This afternoon through Sunday evening)...

The status quo of unsettled weather continues across the Bering
Sea, Aleutians, and Alaska Peninsula (AKPEN). The broad
negatively- tilted trough remains draped across the Bering this
afternoon and looks to stay there through Saturday. As such, the
Western and Central Aleutians and the western/central Bering will
remain unsettled with bouts of showers and rain/snow mix from
time-to-time.

The more active weather continues to be on the eastern side of the
broad trough and towards the AKPEN and eastern Bering. Another
meso-low is currently southwest of Kodiak Island and is tracking
west-northwest towards the southern AKPEN. the strongest winds
are expected to remain northeasterly out of Bristol Bay and
Shelikof Strait. Gale-force winds are expected with also a brief
period of storm-force winds at the southern exit of Shelikof
Strait along the AKPEN. This system moves into the Bering Friday
morning and tracks to the Pribilof Islands Friday afternoon and
evening. Confidence is higher in the storm track staying east of
the Pribilofs and allowing surface winds to persist with a
northerly component. The result will be wet snow Friday afternoon
into the evening and eventually changing over to rain/snow mix
late Friday night as the storm passes by to the northwest and
winds flip to a southerly component.

The next low pressure system arrives to the AKPEN for Saturday.
Confidence continues to be on the lower end of the spectrum with
regards to track. A more northerly track would equate to greater
precipitation chances across mainland Southwest Alaska, while a
more southerly track would mean precipitation is mainly confined
to the AKPEN. With warmer air coming in aloft along with northerly
winds at the surface, the risk could be there for some freezing
rain or wintry mix to fall; especially for mainland Bristol Bay.
Confidence is low currently with guidance disagreements.

As showery rain/snow mix continues along the Western and Central
Aleutians Saturday, a stronger North Pacific and front low will
approach the area Sunday into next week. Storm-force southeasterly
winds along with moderate to heavy rain look to be on tap for the
beginning of the next work week.

&&

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

The long term forecast begins with a low in the Gulf centered
near Kodiak Island. This low will allow for a Gale or possibly a
Storm Force barrier jet to form along the Southcentral coastline.
Gusty winds could even extend into the Barren Islands, and
Shelikof Strait regions. This will all depend on the exact
location and strength of the low which is still uncertain at this
time. As for the West, A col forms over the central Aleutians near
Adak with a deep low to the west. The low will allow for storm
force winds and precipitation in the Shemya region. As the low
travels east, gale force winds will affect the Bering as well as
gap winds Alaska Peninsula near Cold Bay on Tuesday.

Back to the Gulf for Wednesday has a low pushing in from the
Southwest. There is quite a bit of uncertainty regarding its
track, but gale force winds and precipitation are expected to
accompany the low. Upslope flow along the Southcentral coast and
mountainous regions will likely trigger heavier precipitation, but
areas more inland including the Anchorage Bowl will likely stay
on the dry side due to downsloping. A barrier jet may form with
the passage of the low, but like before, this will depend on the
strength and track it decides to take, which is uncertain at this
time. Winds will die down by Thursday as the low dissipates as it
moves inland. As these winds calm down, downsloping will end and
precipitation will finally be able to make it into the Anchorage
Bowl, but exact QPF is uncertain. In the West for Wednesday, the
low will open into an upper level trough and will funnel cold air
from the north. This will allow gale force winds to linger in the
waters west of the Pribilofs and for widespread light snowfall to
occur across the central Bering and into the Kuskokwim Delta
coast. Thursday has cold air advection continuing to filter down
and the 0F line will pass the Aleutian islands, allowing for
widespread but light snowfall. Also, A low will arrive from the
southeast, which has some implications, but it's track is still
too uncertain to make any hard predictions.

-JAR

&&

.AVIATION...

PANC...VFR conditions and northerly winds will persist.
Strengthening easterly to southeasterly winds to around 20 kt to
25 kt aloft could lead to weak wind shear late tonight through
Friday afternoon.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
956 PM AKST Thu Dec 19 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0226 AM     Coastal Flood    Kwigillingok            59.88N 163.16W
12/18/2024                   Bethel             AK   Tribal Leader

            At 2:26am, Kwigillingoks Tribal Resilience
            Planning Assistant reported coastal
            flooding. No damage or significant impacts.
            Snow and ice jams caused minor ponding on
            boardwalks and filled some dry lakes,
            slowing traffic in affected areas.

&&

ME