Small Craft Advisory 57, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 PM AKST Fri Jan 17 2025

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

The primary weather focus through the short term remains the slow
progression of the frontal system and a series of shortwave
troughs and the evolution of a potential low development along
this boundary. Model guidance has trended toward slower
progression of the front into Southcentral Alaska, with broad
support for a developing low near Prince William Sound (PWS) or
eastern Kenai Peninsula Sunday into Monday. This slower evolution
increases confidence in prolonged precipitation along the coastal
areas but introduces significant uncertainty in the timing,
intensity, and inland penetration of precipitation and associated
impacts.

Strong easterly to southeasterly winds this afternoon,
particularly along the Anchorage Hillside and Turnagain Arm, are
expected to persist as a coastal ridge remains along the coast.
While the HRRR (and previously the NAM nest) depicts stronger
winds reaching lower further into Anchorage, other guidance (GFS,
NAM) suggests the pressure gradient will reorient down Cook Inlet
as the low forms. Coastal areas, including Seward and Whittier,
will see steady precipitation as the front lingers offshore.
Precipitation rates will likely increase through Sunday as the low
deepens. Inland areas will remain marginally cold enough for
snow, particularly in locations like Portage through Turnagain
Pass, where low-level thicknesses and temperatures support snow
through the event’s early stages. Portage could see several inches
of snow by Sunday evening, though warm air advection will
gradually erode the cold air, introducing the potential for
rain/snow mix or a changeover to rain. However, downslope effects
along the coastal mountains will continue to limit inland
precipitation, with areas like Anchorage and the Mat Valley
remaining largely dry through much of Saturday. Winds will also
strengthen to near storm-force in the northern Gulf as the front
progresses northward by Sunday morning.

As the trough becomes negatively tilted and the low develops,
precipitation will begin to overspread inland areas late Sunday
into Monday in the Mat-Su Valley, and potentially into the
Anchorage Bowl as well. However, timing discrepancies remain
notable among model guidance. For Anchorage, snowfall remains
uncertain as surface temperatures hover near freezing. Minor snow
accumulations are possible late Sunday into Monday. Marginal
temperatures could lead to variability depending on the timing and
intensity of the precipitation. Valdez will see snow early on
Sunday but will warm with increasing south to southeasterly flow,
with significant snowfall expected for Thompson Pass into Monday.

Overall, the exact timing and strength of the developing low in
the Gulf remain variable across models. The extent of inland
precipitation is tied to how quickly the trough progresses and the
intensity of the cross-barrier flow.

Eovino

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (Friday to Sunday)...

A trough traversing northward across the Eastern Aleutians this
afternoon will continue the gusty southerly winds present in
Alaska Peninsula (AKPEN) bays and passes through tonight.
Locations such Cold Bay and False Pass could see gusts up to 60
mph tonight before a gradual decline through tomorrow. As the low
pressure system moves north, the Southwest coast will see enhanced
southeasterly flow, prompting a Coastal Flood Advisory for the
Kuskokwim Delta Coast through tomorrow afternoon. The highest
threat is especially for the communities of Kwigillingok and
Kongiganak, where the timing of the strongest onshore winds
coincide with high tide.

Moderate to heavy precipitation is likely for the higher
elevations of the AKPEN and Wood River mountains while lighter
more showery precip is possible for much of the rest of Southwest.
Another low crossing the AKPEN tomorrow night will help a
resurgence of weather for the Bristol Bay region.

On Sunday morning a North Pacific low will send its front across
the Western Aleutians. There is some model disagreement about
exact track, but it is looking like multiple shortwaves will
rotate around the low center, bringing enhanced winds and
precipitation to the Aleutian chain as it moves east, making it to
the southern end of the AKPEN sometime Monday morning.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...

The high amplitude weather pattern over Alaska for the past few
days will become more energetic as a number of upper level
shortwaves rotate across the region through the forecast period.
Stormy weather continues through Friday across the Southern
portions of Alaska. An elongated Bering trough reorients across
Mainland Alaska, briefly eroding the the downstream ridge before
continuing into Canada. Additional energy from transient North
Pacific low add to the movement. The ridge reestablishes itself
over the Interior as another trough deepens across the Bering for
Thursday, but back-to-back lows continue through the windflow. The
ECMWF and the EC mean solutions are preferred to cover both
synoptic features and the uncertainty with the finer details.

Some lingering areas of rain occur across the Southcentral coasts
with gusty winds over the Gulf of Alaska. The next low brings
locally moderate rains or rain and snow mixed and gusty winds from
the Central Aleutians to Kodiak Island and Kamishak Bay into
Southwest Alaska Tuesday. Locally heavy rain or rain and snow
mixed spreads Eastward along the Eastern Kenai Peninsula into
Prince William Sound Wednesday, and continuing to the Canadian
Border through Thursday before diminishing. In the West, a well
developed low and front bring heavy rain and gusty winds to the
Western Aleutians Tuesday. This system marches over the Aleutians
and Bering, spreading into Southwest Alaska, Northern AKPEN and
Kodiak Island for Friday

&&.AVIATION...

PANC...Light north to northwesterly winds at the surface with
southeasterly winds of 30-40 kt at or above 1500 ft will
contribute to continued low-level wind shear through Saturday.
Ceilings remain VFR with only a low chance for ceilings to lower
below 5000 ft at times.

&&