Gale Warning 947, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
517 AM AKST Wed Dec 18 2024

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

A shortwave ridge is currently over the region, leading to partly
sunny skies, mostly calm winds and overall dry conditions. This
will persist for most areas through Thursday morning. The next
storm to impact the region can be seen on Satellite in the
Pacific, due south of Southcentral near 40N. This storm will
rapidly move north, reaching the southern Gulf of AK Thursday
morning before pivoting west into or near Kodiak Island. Model
guidance is in exceptionally poor agreement and has differences of
hundreds of miles in storm position by Friday afternoon. This is
due to a large baroclinic zone in the north Pacific right now,
with multiple lows developing along the front, in a region that is
poorly sampled. However, the aforementioned storm is likely to
bring moderate precipitation and strong winds to Kodiak Island
and the Gulf Coast/PWS areas Thursday and Friday as it pivots into
the eastern Bering and/or Bristol Bay. The onset of precipitation
may be snow for the Kenai Peninsula, but easterly winds will
quickly raise snow levels to 1000 to 1500 ft by Friday morning.
Little to no precipitation is expected inland, but cloud cover and
increasing winds through the mountain gaps will increase
temperatures.

The storm on Saturday is also poorly resolved, as differences in
weather models will compound with time. In comparison to guidance
yesterday, there as been a notable shift to the south in the storm
track, with the deterministic model envelop between Kodiak Island
and the southern Gulf, with ensemble multi-member clusters fairly
well grouped to the south of Kodiak. Strong winds and moderate to
heavy precipitation is still expected for Kodiak and the western
Prince William Sound, with chances for rain and/or freezing rain
making over the mountains and into the Cook Inlet areas at times.
Overall model run-to-run consistency is terrible, so pinpointing
weather impacts is difficult at this time, but the signals for
warm and wet weather are ample for this weekend.

-CJ

&&

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

A longwave trough is persisting over the Bering and Aleutians
this morning. The deep occluded low at the heart of the trough,
which is responsible for unsettled conditions throughout the
region, is also persisting. Impressively, an occluded front arcs
from out of the North Pacific, through the Alaska Peninsula, over
the Pribilof Islands and southward through the Central Aleutians
back into the low, which currently sits roughly 40 nm southwest of
Nikolski. It is this front which delineates a baroclinic zone
stretching from the eastern Bering down across the AKPEN into the
North Pacific. Satellite imagery reveals several smaller mesoscale
lows are lifting northward along the front, each with a region of
accompanying gales. A High Wind Warning will be allowed to expire
for the southern Alaska Peninsula shortly as winds are quickly
subsiding with the departure of mesolow departing the AKPEN. Cold
Bay saw peak gusts of around 62 knots (71 mph) during the early
morning hours, with a quick look at recent observations showing
gusts down to around 30 knots.

Model agreement has been substandard as of late with any
similarities amongst model solutions diverging beyond 24 hours.
This has been a headache in the forecast process, with low
certainty in the small scale details, specifically with the
development and movement of each mesolow along the front. Instead,
a broad brush approach has been leaned heavily upon, and this
approach was also used for the morning forecast package.
Essentially, gusty conditions, as well as areas of widespread
showers, will continue along the occluded front. Areas of
southeasterly gales will likely accompany each passing mesolow
from the AKPEN and Eastern Aleutians up into Saint Matthew Island
through tonight.

The occluded low near Nikolski finally lifts northwestward
Thursday morning as it weakens and surface pressure rises to
around 970 mb, which should see winds finally begin to relax over
the eastern Bering. A new trough is forecast to pivot from the
Gulf of Alaska into the Alaska Peninsula on Thursday with flow
over the Greater Bristol Bay region becoming northeasterly. The
biggest concern with the new wind direction will be for elevated
winds, including gales, to exit the Shelikof Strait as far south
as Sutwik Island. A bigger low lifts out of the North Pacific and
into the Alaska Peninsula on Friday, with potential for another
round of elevated winds, though a more easterly wind direction
should preclude a threat of any high winds.

Finally, we are monitoring the potential for coastal flooding
along the Kuskokwim Delta coast. Persistent onshore winds could
see elevated water levels coincide with high tide. There is a high
amount of uncertainty if winds will be strong enough to cause any
impacts.

BL

&&

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

An unsettled weather pattern continues as a North Pacific low
moves into the southeast Gulf late Thursday, crossing the Gulf to
east of Kodiak Island by Saturday morning. This will be followed
by a shortwave on Saturday afternoon, and a second low entering
the Gulf by Sunday afternoon.

Rain will be enhanced by terrain at low elevations and mountain
snows possible for coastal regions, while downsloping should
reduce the amount of precipitation that reaches inland locations.
This pattern is expected to persist through the weekend, with the
strongest winds coming from the east, affecting areas which
include the Barren Islands, Kodiak Island, and Eastern Kenai
Peninsula.

-Baker

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&