Gale Warning 70, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
534 AM AKST Sat Jan 18 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
the 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 Matanuska 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 Valleys, 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 (Saturday to Monday)...

Gusty southerly winds diminish through the day on Saturday as the
responsible low continues north over the Bering Strait. A
compact low crossing the Alaska Peninsula this afternoon will
aid in sustaining moderate to heavy precipitation across the
higher elevations of the Alaska Peninsula and Wood River
mountains, while lighter more showery precipitation will be
possible for much of the rest of Southwest Alaska.

Sunday morning, a North Pacific low tracking eastward, just south
of the Aleutian Chain, will bring another series of shortwaves
north into the Bering Sea, enhancing winds and precipitation along
its path. Colder air will sweep eastward across the Bering,
changing precipitation from rain to snow for the Pribilof Islands
early Sunday morning, followed by the Kuskokwim Delta by Sunday
afternoon.

By the time this system reaches the Alaska Peninsula on Monday
morning, light rain and snow could be possible for all of Bristol
Bay, with inland locations favoring snow. As warm air is drawn in
from the North Pacific, the rain/snow line moves north across
Bristol Bay on Monday. Confidence is high as model agreement
remains good through 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 Sunday.
Ceilings remain VFR. Sunday afternoon, a short period of
precipitation is likely with a front lifting across the terminal.
This is more likely to be snow than rain, but precipitation type
is uncertain at this time. Visibility and ceilings may drop as
low as IFR for a few hours if precipitation falls as snow before
improving back to VFR in the evening as a light southeasterly wind
kicks in behind the front.

Quesada

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
120 PM AKST Sat Jan 18 2025

AKZ102-103-190800-
Anchorage-East Turnagain Arm-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Girdwood, and Portage
120 PM AKST Sat Jan 18 2025

...STRONG EASTERLY WINDS POSSIBLE FOR PORTAGE VALLEY, TURNAGAIN
ARM, AND THE ANCHORAGE HILLSIDE FROM LATE TONIGHT THROUGH SUNDAY
MORNING...

Easterly winds will increase tonight as a system approaches the
region from the south. Expect winds to begin increasing late
tonight and continuing through mid to late morning Sunday before
gradually decreasing. Portage Valley and along the Turnagain Arm
could see sustained easterly winds of 25 to 35 mph with gusts of
45 to 60 mph. Strong winds of 30 to 45 mph with gusts of 50 to 70
mph are possible along the Upper Anchorage Hillside, including
Bear Valley and Upper Potter Valley areas.