Gale Warning 953, NWS Anchorage, AK

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

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

A broad trough extends from the Bering into the southern Gulf while
a ridge exists over the Mainland. A strong low is currently
moving into the southern Gulf and will swing west into Bristol Bay
through Friday morning, passing just south of Kodiak Island.
Gusty winds will continue to pick up on the Island today with
increasingly heavy rain. For the Southcentral Mainland, this
front will swing into the Sound, bringing light to moderate
precipitation to Seward and the Kenai Mountains over the next 24
hours with gradually raising snow levels as warmer air moves in
from the Gulf. Precipitation for the eastern 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 in between storms.

The next storm is expected to take a similar track, moving from
the far southern Gulf, south of Kodiak and then into Bristol Bay.
The overall trend with this system over the past few days has
been to take a more southerly track. 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. With the track being
farther to the south, it's looking like the potential for strong
winds along the Anchorage Hillside have diminished due to a strong
north-south pressure gradient down the Inlet. This 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 and generally speaking the pattern has become less and
less favorable for this scenario.

For precipitation, most of the rain will fall along coastal areas,
though strong shortwaves may spill light precipitation into the
lee-side areas from Palmer south into the western Kenai Peninsula.
Timing of these features will dictate whether or not this falls
as freezing rain or rain. Current forecast thinking is that
temperatures will be in the mid-30s due to winds mixing in warmer
air through the mountain gaps prior to the onset of precipitation
later in the day on Saturday. However, areas that are more
sheltered from the wind may still 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. One other area
to note will be Valdez. If winds fail to warm the Fjord from the
Lowe Valley, increasingly warm air aloft may cause precipitation
to fall as freezing rain. This is always a hard forecast to make
due to the poor resolution within the complex terrain and the fact
that Valdez tends to hold onto cold air better than most areas.

-CJ

&&

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

There is a broad trough currently stretching across the
Aleutians, bringing gusty winds and rain/snow shower activity to
the chain. Multiple shortwaves embedded within it will rotate
around cyclonically, locally enhancing wind and precipitation as
it traverses westward into Saturday.

A Coastal Flood Advisory is in effect through 11 AM AKST this
morning to address minor flooding in low-lying areas around
Kwigillingok. With lowering tides and decreasing winds pushing
further offshore in the coming days, we do not expect any further
flooding for the Northern Kuskokwim Bay.

A low pressure system currently in the Gulf of Alaska will cross
over the Alaska Peninsula (AKPEN) into the southeastern Bering Sea
Thursday night. Model agreement regarding this system has
improved with the last few runs, and we expect gale-force winds
and rain showers across the Bristol Bay marine zone Thursday night
into Friday morning. Steady easterly winds should limit the
threat of freezing rain for mainland Bristol Bay, but we can't
totally rule out the possibility of some light precip. Upslope
flow against the Wood River Mountains will increase chances for
nearby communities.

The next big player in Southwest Alaska weather comes in the form
of a poorly resolved low moving south of Kodiak Island Saturday
morning. The finer details are fuzzy, but the general
northwestward track across the AKPEN will bring elevated winds to
the Bristol Bay mainland and marine zones for the majority of the
day Saturday. The highest amounts of precipitation will fall on
the Aleutian and Alaska Ranges while the AKPEN and Aleutian
Islands will continue to see shower activity through the weekend.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

The persistent pattern of troughing across the AKPEN continues
early in the period. The pattern weakens and allows a North
Pacific low to move into the central Gulf by Monday, pushing into
the northern Gulf on Tuesday and Wednesday.

As the low organizes over the northern Gulf, rain, snow and windy
conditions can be expected. Precipitation will be enhanced by
terrain for coastal regions. Some downsloping should reduce the
amount of precipitation that reaches inland locations, with the
pattern forecast to persist late in the week.

Baker

&&

.AVIATION...

PANC...VFR conditions and northerly winds will persist.
Strengthening easterly to southeasterly winds aloft of about 20
kt could lead to weak wind shear though Friday afternoon.

&&