Gale Warning 360, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 PM AKDT Thu Apr 4 2024

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

A high amplitude but progressive pattern is in place aloft, with a
ridge extending from the NE Pacific to the ALCAN border and a deep
trough over much of the Bering Sea/Aleutians and the western
Alaska Mainland. A series of short-waves have been tracking up
and over the west side of the ridge, traversing the western Gulf
and Southcentral. This has resulted in periods of mostly light
precipitation across Southcentral today. Warm air advection has
been enough to change precipitation to rain across portions of the
Kenai Peninsula and Gulf coast. As you head north and inland,
precipitation is falling as all snow. Snow accumulation has been
light, with some melting when snow lightens up. Temperatures are
around or a bit above freezing and despite the overcast skies
enough solar radiation is making it through and helping melt snow.
The pattern looked favorable for a Turnagain wind to bend into
south to west Anchorage and cause snow to mix with rain. However,
that has not occurred and is looking less likely - so
precipitation may stay in the form of snow.

The upper level ridge and trough will progress eastward tonight,
with the tap of deep moisture between the two shifting to the
northeast Gulf and Southeast Alaska. A series of short-waves will
continue to track across Southcentral. One slightly strong wave
will become negatively tilted as it moves over the Kenai Peninsula
Friday. The southern portion of the trough will dig across the
northern Gulf, while the northern portion stalls over the Kenai
Peninsula. The big ramification of this is a more prolonged
period of snow for Anchorage and the Mat Valley, with snow
lingering all the way through Friday afternoon or evening. Have
upped snow totals quite a bit in this region, with highest amounts
along and near the Chugach Mountains, including the Anchorage
Hillside and Eagle River. Snow amounts across the rest of
Southcentral will generally be light. Precipitation will linger
longest from eastern Prince William Sound to the Copper River
Basin as one final short-wave rotates through the area Saturday.

Attention will then quickly shift to a strong front moving out
ahead of a deep low along the Aleutians. A triple point low will
form south of Kodiak Island Saturday morning and track into the
Gulf Saturday night/Sunday. While models do diverge a bit on the
track of the low, there is a trend toward a more southerly track
across the Gulf - driven by a zonal jet aloft. Based on this, the
vast majority of precipitation and wind with this system will be
confined to Kodiak Island and the Gulf, with perhaps some
precipitation for the north Gulf coast/eastern Kenai Peninsula
along the northern periphery of the system this weekend. Dry
conditions will settle in across inland portions of Southcentral
for the weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA, BERING SEA, AND ALEUTIAN
ISLANDS (Days 1 through 3: Tonight through Sunday)...

A broad trough extends its influence across the Bering Sea and
Southwest Alaska this afternoon. A long fetch of southwesterly
winds and weak cold air advection is leading to a mix of rain and
snow showers, particularly along the western slopes of mountains
throughout Southwest Alaska. This general pattern continues
through Friday, with lower elevations likely to see periods of
shower activity with the passage of weak disturbances propagating
through the flow. The strongest of these features, currently
located over the northwestern Bering Sea, will swing eastward to
bring a round of light snow to the Kuskokwim Delta region tonight
into Friday morning. Rain and snow showers transition back to all
snow with gradually cooling surface temperatures into the weekend.
The persistent fetch of southwesterly winds may also generate
some minor coastal storm surge impacts through tonight, with some
potential for water levels reaching 1 to 2 feet above highest
astronomical tide. With shorefast ice along much of the Kuskokwim
Bay coastline, the main impact is likely to be some water pooling
on the icepack.

A strengthening North Pacific low also approaches the western
Aleutians tonight, pushing its warm and occluded fronts across the
chain into Friday. The low strengthens into the upper-960s mb,
with a pressure gradient driving high-end storm force winds along
the south side of the low as it moves into the western Bering Sea
on Friday. Confidence has increased that the swath of strongest
winds moves through the central Aleutians on Friday night, with
high potential for wind gusts of 75 mph or greater in Adak and
Atka. Initially southwesterly winds will gradually shift out of
the west, which is a favored direction for strong wind events in
both of these Aleutian communities. A High Wind Watch has been
issued to highlight this threat.

The low's triple point dips south and east as the low occludes
through Saturday, meaning that the warmest air will remain across
only the furthest south portions of the domain. As a result, the
Pribilof Islands are likely to see blowing snow with the passage of
the front, though temperatures above or near freezing will likely
limit its ability to reduce visibility as low as one half mile.
While precipitation falls as rain along the Aleutians for Friday,
snow mixes in Friday night for the southern Alaska Peninsula, and
precipitation likely falls as all snow for the northern Alaska
Peninsula and Bristol Bay on Saturday. Temperatures will be colder
further north, so there remains some potential for blowing snow
along the northern coast of Bristol Bay, particularly near
Platinum and Goodnews Bay, where easterly winds may gust as high
as 35 to 40 mph.

By Saturday night, the weakening low sinks south across the
eastern Aleutians/Alaska Peninsula into the North Pacific,
bringing widespread rain and snow showers to these areas as its
front weakens along the northern Bristol Bay coast. Behind the
low, colder air filters south across the Bering Sea for Sunday,
allowing for some light freezing spray along the ice edge as
precipitation trends down across the forecast area.

&&

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

The upper level trough extending from the Arctic through the
Mainland into the Gulf of Alaska gets a reinforcing boost by
Tuesday. A Chukchi Sea low rides along with Western Alaska Arctic
air to intensify the Gulf low through midweek. This uptick will be
brief as the low becomes an open wave and moves into the Yukon
Territory by the end of the week. A moderate amplitude ridge over
the Bering will flatten out in the Western Gulf by the end of the
forecast period as another low out of Eastern Asia drives into the
Western Bering by Thursday. Good deterministic model handling
continues through the transition to ensemble means by the end of
the forecast period.

The Chukchi low brings another round of Arctic air over Western
Alaska that is expected to spread further inland through the
period. Gusty Northerly winds along the West coast may affect ice
coverage over the Eastern Bering through Thursday. Gusty winds
spread over Southwest Alaska and the Alaska Peninsula and over
Kodiak Island and the Southern Kenai Peninsula through Wednesday.
Widespread precipitation starts as snow that becoming mixed with
rain across Kodiak Island and Southcentral Alaska through
Wednesday. Rain extends across the Southcentral coasts, with snow
more likely inland. A new front moving over the Western Aleutians
and Bering Tuesday strengthens during its Eastward push into
Western Alaska and the AKPEN by Thursday. Snow is expected over
the Bering, mixed rain and snow for the Aleutians and AKPEN.

Kutz

&&

.AVIATION...

PANC...Snow, possibly mixed with rain during the late afternoon
and early evening, is expected to continue through the TAF
period. Timing of the heaviest precipitation is difficult today.
At this time, it appears to be late afternoon into evening,
however there are concerns of a band of precip setting up
somewhere across the region overnight. CIG/VIS will generally be
MVFR, except during periods of heavier precip. Turnagain arm
winds are expected to affect the terminal from time to time late
this afternoon/evening.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1159 PM AKDT Thu Apr 4 2024

AKZ102-060600-
Anchorage-
Including the cities of Anchorage, Eagle River, Indian,
and Eklutna
1159 PM AKDT Thu Apr 4 2024

...AREAS OF LIGHT TO MODERATE SNOWFALL EXPECTED TO CONTINUE
THROUGH FRIDAY AFTERNOON...

A band of steady snow has developed over Anchorage this evening
and is expected to persist through much of the day on Friday.
Snowfall may gradually taper off as early as Friday morning on the
west side of town, but will likely persist well into Friday
afternoon across East Anchorage.

Additional snowfall accumulation through Friday afternoon of 2 to
5 inches is expected, with higher amounts up to 9 inches possible
across the Anchorage Hillside. Expect difficult travel conditions
across Anchorage where heavier snowfall persists, especially
during the Friday morning commute and towards the east side of
town.