Small Craft Advisory 29, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 PM AKST Tue Jan 11 2022

.ANALYSIS AND UPPER LEVELS...

A broad upper low is anchored along the Pacific side of the
Aleutian Chain with an upper-level ridge extending along the
Canadian Rockies. Between these two long wave features, a
southerly flow is helping drive a series of shortwave northward
from the Pacific across the Gulf and over the Southern Mainland.
The first of these waves is draped along the Southcentral coast
is pushing a band of light snow into interior Southcentral. As it
does, light snow is coming to an end across the Kenai Peninsula.
Light snow, however, lingers across the Anchorage Bowl and is also
continuing throughout the Mat-Su Valleys. Farther east, a band of
mixed rain and snow across Prince William Sound is falling apart
and becoming more showery in nature as it, too, moves north and
colder air aloft begins to wrap in behind the shortwave.

Out west, clouds persist across much of Southwest Alaska, as a
transient ridge moves through the region, trapping lingering low-
level moisture in a wake of a shortwave that moved through
yesterday. Conditions also remain unsettled across the Chain as a
vertically stacked low spins near Dutch Harbor. Colder air is
beginning to wrap around this low, with temperature that were in
the lower 40s yesterday across the eastern half of the Chain
slowly falling back into the mid 30s. Temperatures across the
western half of the Chain are slightly cooler, mainly in the upper
20s to lower 30s, with scattered snow showers and northerly
winds.

&&

.MODEL DISCUSSION...

Timing and strength of shortwaves embedded in the long wave
pattern continue to be the main discrepancies in the models. This
issue is most pronounced with the wave moving to the Southcentral
coast for Wednesday afternoon. The NAM continues to be the most
bullish with this feature, but has backed off on the extent of
precipitation with it latest 18z run. Models are also coming into
better agreement with a developing storm-force low moving from the
North Pacific to an area south of Kodiak Island for late Thursday,
although differences remain as to the timing and position of the
front as approaches the coast.

&&

.AVIATION...

PANC...

Any lingering light snow will taper off through the afternoon
hours. Visibilities and ceilings will improve to VFR as snow
comes to an end. Some low stratus is expected to linger across
Cook Inlet and around the terminal through the evening and
overnight hours. The short term forecast challenge is whether
this FEW to SCT deck fills in and results in a return of IFR
ceilings through early Wednesday morning. Given the expanse of
low stratus farther south over the Inlet, the forecast reflects a
return of IFR ceilings this evening, especially after sunset and
the expectant tapering off of the light southerly winds. If this
low ceiling does develop, there is also the potential for periods
of very light drizzle/freezing drizzle. Confidence with this,
however, is low.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Tuesday
evening through Thursday)...

Unsettled weather will continue through the end of the week. A
few weak pulses of energy will move over Southcentral tonight,
allowing rain and showers to linger over coastal areas and the
mountains. Monday morning a more significant wave extending east
from a nearly stationary upper low over the Central Aleutians will
move over the region from south to north. This wave has trended
farther to the east, resulting in likely precipitation over the
western Kenai Peninsula mid to late afternoon. Some solutions
bring some light snow into Anchorage and the Mat Valley as well,
but these remain the outliers. At this time precipitation with
this wave is expected to remain as snow. With the broad south to
southeast flow, another round of heavy mountain snow and coastal
rain is also likely for the Prince William Sound areas.

On Thursday a strong low is expected to slowly move to the south
of Kodiak Island as its front sweeps north to the Gulf Coast.
Precipitation type will begin as snow or rain and snow for
coastal areas and transition to rain below 700 to 1000 ft by
Thursday afternoon. This will likely cause snow covered roadways
along the Seward Highway to become slick once again. In many ways,
this storm will be very similar to the weather over the past 3
days, with heavy snow in the mountains and rain at sea level for
coastal areas. The Cook Inlet Region is expected to remain
downsloped once again. The primary difference will be the absence
of an arctic airmass over the interior, so strong outflow winds
are not expected and freezing rain should be less prevalent,
though rain falling on frozen surfaces may still cause some
issues for the eastern Kenai Peninsula.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 through 3: This
afternoon through Friday)...

Relatively quiet weather tonight but another round of light snow
expected Wednesday.

The next upper level shortwave will push a front through
Southwest Alaska on Wednesday with periods of light snow across
Bristol Bay during the morning and shifting towards the Kuskokwim
Delta Wednesday afternoon and Wednesday night. Most populated
locations will receive 1 to 2 inches of snow. Otherwise expect
temperatures to be a bit warmer on Wednesday. Thursday will be
relatively quiet as another low pressure system develops south of
the AKPen. This system will bring increasing winds Thursday
afternoon for Bristol Bay and slightly warmer temperatures due to
downsloping effects near King Salmon and Iliamna. There will be
some light snow north and west of Dillingham by Thursday afternoon
due to upslope effects with an inch or two of snowfall possible.

A bit of uncertainty on Friday as a low south of the AKPen tracks
towards the area. Models disagree on timing and where the low
will track which will alter where and when snow and rain occurs.
Overall snowfall should be less than three inches for most areas.
Stay tuned as we refine the forecast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Day 1 through 3: This
afternoon through Friday)...

A weakening low near the Central Aleutians will remain nearly
stationary tonight and dissipate by Wednesday with Gales weakening
to small crafts near this low. Gales will develop over the
northern Bering due to cold air moving from the Arctic regions
this will also cause heavy freezing spray, especially in areas
where the crab fishermen like to fish this time of year. Expect
these conditions to continue Wednesday and Thursday before winds
decrease and heavy spray lessens over the northern Bering by
Friday. Otherwise a low pressure system developing over the
northern Pacific will move towards the southern AKPen bringing
Gales and rain Wednesday night and Thursday.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Going into the weekend, an upper trough stretching across Bristol
Bay to the Eastern Gulf will bring periods of unsettled weather
with rain and snow showers to the Southwestern Alaska and Gulf
coastlines through the weekend. Winds will remain below gale force
over the Gulf with seas on Friday around 15 ft subsiding to below
10 ft on Sunday. However, to the west, another cluster of
elongated troughs along the Aleutian chain will very slowly move
east, with gale force winds approaching storm force in the western
Aleutians. These winds will increase seas to around 20 ft at
times south of Aleutians and in the Bering Sea throughout the
weekend.

&&

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

The relatively warmer and wetter pattern experienced this week
will continue through this weekend. Periods of rain and snow
showers, which could be heavy at times will be possible along the
Gulf Coast and Southcentral Saturday. A brief period of dry
weather is possible Sunday through early Monday across
Southcentral. Rain and snow from another elongated low stretching
along the southern portion of the Aleutians into the Bering Sea
will gradually push precipitation east along the Aleutian chain
towards Southwestern Alaska this weekend into early next week.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 130, 132, 138, 150, 155, 177, 185,
         351, 352, 413.
         Heavy Freezing Spray: 185, 412, 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...VR