Storm Warning 195, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 PM AKST Thu Dec 12 2024

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

Discussion:

The low that has moved westward across the northern Kenai
Peninsula throughout the day today continues into the Cook Inlet
where it stalls and weakens tonight, leaving a trough lingering
over the area through mid-morning Friday. Showers continue to
stream into Prince William Sound from the Gulf through tomorrow
morning, with rain near sea level transitioning to a rain/snow mix
or snow this evening through tonight. Elsewhere, steadier
precipitation continues to fill in over the western Kenai
Peninsula this afternoon as the low pulls away to the west,
bringing light rain from Kenai to Seldovia with snow at higher
elevations. Areas near sea level are expected to transition from
rain to a rain/snow mix this evening, while snow continues further
inland and at higher elevations. Precipitation chances across the
Kenai Peninsula will decrease this evening, with the southwestern
Kenai Peninsula hanging on to the greatest chances for rain and
snow into early Friday morning. After the dissipation of the low,
drier conditions are expected through Saturday except for some
light snow showers possible for the Copper River Basin.

By Sunday morning, an upper level low dropping southwest into
Interior Alaska will help reestablish a cooler airmass over
Southcentral and will promote potentially gusty northerly winds
thorough favorable gaps and Thompson Pass. All longer range models
show this feature, but they have yet to converge on a defined
track and placement of the upper low. It is appearing more likely
that the ridge in the Gulf will prevent the upper low from digging
farther south than the Copper River Basin, though shortwaves
rotating around the low may aid in the development of a weak
surface low or trough in the northern Gulf. The current trend
favors the eastern Prince William Sound to see the greatest
precipitation, likely falling as all snow.

-JH

&&

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

The Southwest mainland is mostly quiet with the exception of the
lower Kuskokwim Valley, which is receiving snowfall due to a
shortwave backing into it from the east. Snowfall totals are
expected to be slightly higher than before, now at 3-5 inches. The
snowfall is expected to continue until early afternoon on Friday.
Afterwards, ridging will build into the mainland Saturday through
Sunday, which will diminish chances for precipitation. Cold air
advection will filter into the Southwest Mainland on Saturday,
which will allow high temperatures to drop to the teens in the
northern regions and the 20s in Bristol Bay and the Alaska
Peninsula. At the end of the short term period, a low from the
east will back north of the region and will bring a chance of
snowfall for the northernmost areas of the Kuskokwim Delta.

The Bering is a lot more interesting. A short period of showery
weather is taking place in the Eastern Aleutians and the Southern
Alaska Peninsula due to a frontal system that is passing by.
Ridging follows this front and will diminish chances for
precipitation for Friday. This will be short-lived as another
front pushes in from the west. This front is currently over the
Western Aleutians and is bringing rainfall and gale force winds to
the Shemya region. The front will weaken as it moves east, but
will allow for precipitation across the Aleutians on Saturday.
Gale force winds will reach the Pribilof Islands but elsewhere
will see small craft winds. A North Pacific low rises south of the
Eastern Aleutians on Saturday night, but never reaches the coasts.
However, a band of precipitation from the low will reach the
state and will allow for light precipitation from the Alaska
Peninsula to the Kuskokwim Delta coastline. Finally, a very
strong storm force low will arrive from the southwest into the
Shemya region and will bring heavy rains and gusty winds as it
makes its way east. Wind speeds will weaken as it moves east but
the Shemya and Adak areas could even see hurricane force winds. We
will continue to monitor this low's development, so stay tuned
for updates.

-JAR

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

The long-term forecast on Monday should begin with high pressure
situated over interior Alaska and along the ALCAN border.
Meanwhile, a large occluded low is forecast over the Western and
Central Aleutians with the front extending southeastward from the
Pribilof Islands to across the Alaska Peninsula. Thus, a very
active pattern should continue across the Bering and Aleutians
with windy conditions and numerous showers (a mix of both rain and
snow) to linger through Tuesday.

Forecast confidence is low with resolving the finer details. It
is increasingly likely that one or multiple lows will develop on
the Pacific side of the Aleutians before wrapping north and
northwestward into the parent upper low over the Bering Monday
through Wednesday. A brief break from unsettled conditions may
develop across the Bering on Thursday as high pressure develops
behind a departing trough into the Gulf of Alaska and the next
upper low into the western Bering.

Elsewhere, all indications are that Southcentral will retain
above normal temperatures with continued southerly flow into the
region. After starting out the period relatively dry on Monday, a
series of lows are progged to lift northward into the Gulf Tuesday
and then again on Thursday. This will result in potentially heavy
shower activity at times, especially into the Gulf coast.

-BL

&&.AVIATION...

PANC...The latest forecast backs off on precipitation chances and
maintains VFR ceilings/vis. A low will continue to spin over Cook
Inlet and the Kenai Peninsula tonight through Friday morning
before dissipating. Showers will rotate around the low center,
but it looks less likely for any steady precipitation to affect
the terminal. If precipitation does fall, it would fall in the
form of snow, which could briefly lower ceiling/vis, but there is
a low probability of this occurrence. The upper low and short-wave
will exit southward tomorrow (while the surface low dissipates)
and high pressure will build in aloft. This could trap low level
moisture and lead to lowering of ceilings some time tomorrow
afternoon or evening. For now, will hold off on introducing low
clouds, but will continue to evaluate this potential.

&&