Small Craft Advisory 12, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 AM AKST Wed Jan 4 2023

.ANALYSIS AND UPPER LEVELS...

A longwave trough extends from the Bering to the Gulf of Alaska
and the jet core is well south of the Aleutian chain near 35N
latitude. There are numerous major and minor shortwaves embedded
within the pattern. There is a gale force low over the northern
Gulf of Alaska. The Kenai and the King Salmon radars have been
active early this morning. On satellite imagery, there is a broad
swath of cold air stratocumulus from the North Pacific into the
Bering with an occlusion over the Gulf and another occluded system
over the Western Aleutians. The ice shield continues to grow over
the Northern Bering through Bristol Bay.

&&

.MODEL DISCUSSION...

At the onset of the forecast period there are some minor
differences with the placement of the surface low in the northern
Gulf and with the lows over the Western Aleutians. By 12z Thursday
the divergence in solutions amplifies. This creates some
uncertainty. Hoever, even with the vagaries of the models, the
trend is toward stronger lows the remainder of the week.

&&

.AVIATION...
PANC...There is a surface low south of Homer and the models bring
precipitation into the northern Cook Inlet. Showers will be
possible at PANC. As the low passes just south of the Kenai
Peninsula early tomorrow, strong easterly winds will begin to
cross the Chugach and Kenai Mountains, which should lead to a
brief period of low level wind shear. VFR conditions expected much
of the TAF package although a period of MVFR conditions is
possible. Amendments will be made as needed.

&&

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

The strong low that was in the Gulf of Alaska yesterday has
weakened considerably and is tracking westward over the Barren
Islands region (between the southern tip of the Kenai Peninsula
and Kodiak Island) early this morning. This low is bringing a
rain/snow mix to Kodiak Island as well as the Kachemak Bay area
with rain along the eastern Kenai Peninsula in the warmest sector
of the low. Areas to the lee of the Chugach and Kenai Mountains
are mainly dry this morning due to the downsloping from cross-
barrier flow overriding the lifting from the low. For the Copper
River Basin., there has been large areas of clear skies which has
dropped temperatures below zero across much of that region this
morning.

After this low moves westward and dissipates tonight, Southcentral
will be in generally southeasterly flow aloft. However this flow
is not associated with a warm tap of moisture from the south and
is actually wrapping in cooler air that originated in the Bering
Sea that too k the long way around into the Gulf of Alaska and
Southcentral. Therefore, temperatures will creep lower the next
few days especially during any overnight periods of clear skies.
The item to keep and eye on the next few days will be the
potential for a shortwave to develop and ride up the southeasterly
flow and bring an area or two of snow showers. There is nothing
that looks very likely to develop and do this at this time, but it
is certainly possible in this overall pattern. Other than that,
Thursday should have rather mild weather and temperatures for
most of Southcentral with cooler conditions shaping up for the
weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Friday night)...

An active pattern for Southwest Alaska looks to continue through
the workweek as a low pressure system approaches the Alaska
Peninsula (AKPen) from the Gulf of Alaska. This low has already
sent high clouds over the mountains into Southwest and a
deformation band along the leading edge of the low will breach the
AKPen into the Greater Bristol Bay area by this afternoon. This
will bring steady snowfall from Iliamna to Igiugig and from King
Salmon to Koliganek from this afternoon until tomorrow morning.
Snow is likely to reach Dillingham during this similar timeframe,
however precipitation will likely be showery in nature.
Accumulations across the Greater Bristol Bay area will be light,
1-2 inches. As this system moves northward it will weaken,
bringing only a slight chance of snowfall to places like Bethel on
Thursday.

Steady offshore flow into Bristol Bay will ease with the exit of
the low Wednesday. Calm winds are expected throughout much of
Southwest through Thursday. Areas of fog are expected to set up
across coastal Southwest through Wednesday morning. Temperatures
are expected to steadily grow colder as the weekend approaches.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Today through Friday night)...

An unsettled weather pattern persists across the Aleutians and
Bering. A decaying low pressure system in the Eastern Bering as
well as a trough extending from the Kamchatka Peninsula into the
Central Aleutians have, and will continue to, promote an
unsettled, unorganized regime through the end of the workweek.
Multiple embedded lows within the aforementioned extended trough
have broken up the structure of what was once a frontal boundary
and are pushing mild showery conditions from the Western Aleutians
eastward. Precipitation associated with this complex system is
expected to remain as snow. Periods of Small Craft Advisory winds
will accompany the weak low complex during its eastward
advancement. These lows will reach Atka by Thursday morning before
pushing showers northward towards the Central Bering. The next
system to enter the fray will be a North Pacific low that will
approach the Western/Central Aleutians by Thursday evening
bringing mixed precipitation and snow to this area that will
persist through the start of the weekend.

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

The general consensus in the long-term points to a longwave trough
pattern with a series of weakening low pressure systems moving
along the northeast Pacific and the Bering Sea, with high pressure
building over Siberia and Interior Alaska. There is quite a bit
of disagreement this far out in time, with the GFS being the
biggest outlier currently, with a deeper low dragging south of the
Aleutian Chain. As it stands now, precipitation impacts look to
be primarily along the coast, with the bulk of it along the
Southeast Panhandle. But due to inconsistencies among the models,
confidence remains on the lower end. Further inland is likely to
see a drier trend as high pressure lingers over the Interior. The
Aleutians may see more unsettled weather, especially with the
further north GFS trend, later in the week. Overall, patterns look
to be relatively climatologically normal.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray 185. Gale 120 130 131 139.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CL
LONG TERM...KM