Small Craft Advisory 47, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 PM AKST Mon Jan 17 2022

.ANALYSIS AND UPPER LEVELS...
Southcentral Alaska is seeing quiet weather and seasonable
temperatures today as an upper level ridge passes over the
region. Areas of fog and low stratus continue to linger,
especially across Anchorage, Cook Inlet, Kenai Peninsula, Copper
River Basin, and Susitna Valley. Sunshine and an upper level
shortwave are working together to diminish the areal extent of the
fog and stratus, but this will likely not be strong enough to
completely clear out the region today.

A weakening, stacked low near the Western Aleutians continues
pushing its front east towards Southwest Alaska/Alaska Peninsula
and north towards St. Matthews Island. This front is bringing rain
and a rain/snow mix to locations along the Central and Eastern
Aleutians and across Bering, such as the Pribilof Islands. Ahead
of the weakening front, pockets of fog and low stratus linger
across the Kuskokwim Delta and Bristol Bay coasts, though
increasing winds ahead of the front are working to dissipate the
fog late this morning and early afternoon today.

&&

.MODEL DISCUSSION...

Models are not resolving the current fog/stratus over southern AK well.
With continued mid-upper level ridging tonight, and given the
short days of mid-January, a persistence forecast was used
bringing fog/stratus back in tonight.

Model spread has actually increased for the track of weak, upper
level short waves tracking northeastward along the Alaska
Peninsula and towards the Gulf on Tuesday and Wednesday. Thus,
forecast confidence is low over Southcentral for this time period,
and it’s currently difficult to pinpoint exactly which areas
will and will not see precipitation with these features. There is
good model agreement for a robust positively tilted trough sliding
towards the Alaska Range from the north Interior by Wednesday.
This will serve to ferry more of the moisture from the N
Pacific/Gulf of AK towards Kodiak and the Kenai Peninsula. Out
west, model guidance remains in good agreement on another low
moving north towards the Western Aleutians and a front transiting
over the Central Bering on Tuesday.

&&

.AVIATION...
PANC...IFR/LIFR stratus is expected to drift back in, but timing
remains uncertain. While surface moisture values look lower than
last night, fog off the Knik Arm will remain a threat. Conditions
should improve around daybreak Tue morning with better mixing
moving into the area.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Thursday afternoon)...

While much of the fog has dissipated, the same upper level ridge
remains in place along with weak surface flow. As such, periods of
significantly reduced visibility remain possible for the morning
commute on Tuesday. Patchy fog is also likely over low-lying areas
in the Copper River Delta. A front remains on track to enter the
Gulf early Tuesday morning. Light snow accumulations are possible
in Kodiak, however precipitation should quickly change to a mix or
all rain by afternoon. As the front moves farther north, snow
will extend across the Gulf coast, however as its center remains
well offshore, amounts will not be overly impressive, with highest
totals likely near western Prince William Sound. While much of
Anchorage and the Mat-Su will remain downsloped, snow is still
possible late Tuesday into early Wednesday as an inverted trough
develops at the surface in combination with moist flow aloft. The
synoptic southeasterly surface winds are relatively weak.
Conditions on Thursday will again be quiet over Southcentral as
an upper ridge again builds over the region. The next system will
enter the Gulf on Thursday morning which looks to bring a very
deep fetch of moisture to the Gulf coast by the end of the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Thursday)...

A weakening front ahead of a low in the western Aleutians will
bring a chance of rain along the AKPEN for the rest of tonight as
warmer air remains in place. As the front pushes northward,
expect light snow and gusty winds at times across the coastal
areas of the Kuskokwim Delta and Bristol Bay. Surrounding high
elevations will also get a brief shot of snow before the front
falls apart. Meanwhile, a positively tilted trough moving across
the northern half of the state combined with enough moisture will
also bring a light steady snow in the Lower Kuskokwim Valley
beginning Wednesday afternoon and lasting through Thursday. By
Thursday afternoon, models are hinting a strong North Pacific low
and its associated front to trek across the western Gulf, but
deviate on the overall track, position, and how much moisture is
expected for the coastal and valley regions. Uncertainty emerges
as far as how much warmer air will replace the colder air that
will change the precipitation type and amount as well. Stay tuned
as we refine the forecast later this week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Thursday)...

The main weather driver is associated with a broad trough of low
pressure in the western Bering. A series of upper level waves
pivoting around the eastern periphery of this trough will keep
unsettled conditions for much of the Aleutians Chain and Bering
Sea. Additionally, expect a persistent easterly-northeasterly gale
force winds, elevated seas above 20 ft, and rain/snow mix in the
northern Bering to continue over the next couple of days.
Meanwhile, another North Pacific low with its associated front is
expected to bring small craft to gale force winds and rain for
the rest of the eastern Bering/Aleutians beginning on Thursday.

&&

.MARINE (Days 3 through 5 - Thursday through Saturday)...

Gulf of Alaska: A front will advance northeast across the Gulf on
Thursday, and then approach the North Gulf Coast by Thursday
evening. Expect a narrow zone of easterly gale force winds to
develop just offshore with a barrier jet, or between Prince
William Sound and Middleton Island and south of the Kenai
Peninsula from late Thursday into Friday morning. Northeast winds
to gales will also be possible near the southern Cook Inlet and
near the Barren Islands during the same timeframe. The winds will
diminish on Friday as the front falls apart, with weaker southerly
winds and seas of 15 to 20 ft spreading over the rest of the
Gulf. Another weak front or low will move into the western Gulf on
Saturday, though currently expect winds with this next system to
be under gale force with seas less than 20 ft across the entire
Gulf Saturday. However, forecast confidence is notably lower for
this second system at this time.

Bering Sea: Northeasterly winds will drop below gale force early
in the day on Thursday, with seas less than 20 ft and winds less
than 35 kt overall expected to prevail through Friday. A North
Pacific low will approach the central Aleutians from the south on
Saturday, potentially sending easterly gale force winds into much
of the southern Bering. Confidence through Friday is high, but
becomes much lower for the North Pacific low and any winds to gale
force on Saturday.

&&

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

Struggles with more near-term pattern complexity are keeping much of
the long range out of focus for the moment, although the largest
and most important synoptic driver still looks on track to keep a
warm/wet theme in play for much of the southern mainland. Models
continue to shift wildly around for what will be an ongoing
interaction between two systems at the start of the period on
Friday over the Bering. A polar low drifting out into the northern
Bering from the Seward Peninsula will likely become entangled
with another low pivoting north past the eastern Aleutians and
southern Alaska Peninsula, with the two centers eventually at
least partially merging and moving north and one system towards
the Bering Strait through Saturday. Consistency across models and
between runs for this evolution both remain poor, resulting in
diverging solutions for much of the smaller scale details for
nearly the entire outlook area. One feature that remains better-
resolved is the strong longwave ridge that will develop earlier in
the week over the eastern Gulf and much of the eastern mainland,
with the consensus being that this ridge will remain in place into
early next week. A series of shortwaves will attempt to work
around this ridge from the North Pacific through Monday as they
traverse deep, warm southerly flow, with each system helping to
draw enough warm air north to change snow over to mainly rain
along the immediate Gulf coast. Rounds of mixed precipitation are
also likely for the eastern Aleutians, Alaska Peninsula, and
Southwest as each system moves north around the ridge. However,
precipitation will be more light and showery over parts of
interior Southcentral due to the southerly cross-barrier flow and
downslope drying. Above normal temperatures over Southwest and
Southcentral continue to be anticipated throughout the entire
extended period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 176-178 185.
Heavy freezing spray 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
MARINE/LONG TERM...AS