Small Craft Advisory 22, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKST Fri Jan 6 2023

.ANALYSIS AND UPPER LEVELS...

A longwave trough extends from the Bering to Southcentral Alaska
with the jet core continuing to remain south of the Aleutian
chain near 35N latitude. The jet core has an estimated magnitude
of 175 knots. There are numerous shortwaves embedded within the
pattern spanning from Kamchatka to Prince William Sound. The
the King Salmon radar has pinged into isolated light returns
early this morning while the Bethel and Middleton Island radars
remain out of service. On satellite imagery, there is a front over
the Western and Central Aleutians.

&&

.MODEL DISCUSSION...

The run to run continuity with the models has been decent
regarding activity over the Aleutians and the concept of bringing
an inverted trough into the Gulf Of Alaska. Generally speaking,
there has been some level of improvement with the models but there
are some minor discrepancies regarding the timing of shortwaves
and the precipitation fields.

&&

.AVIATION...
PANC...On nighttime microphysics imagery there is some fog/low
stratus near PANC. It is actively being monitored. By 18z, expect
VFR conditions and light winds will persist.

&&

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

Overall clear and cold conditions are occurring over Southcentral
Alaska this morning. Some areas of fog have developed in the
Anchorage area as well eastern Turnagain Arm and lower elevations
of the Copper River Basin. This pattern is creating some gusty
northerly winds through channeled terrain for the north Gulf coast
so Seward, Whittier and Valdez will see some gusty winds today.,
However, these winds will diminish when the inverted trough moves
through on Saturday afternoon or Saturday night depending on
location and speed of passage for this feature.

Some high cirrus clouds can be seen on satellite moving toward
the far eastern portions of Prince William Sound and the Copper
River Basin. That batch of cirrus will not produce any
precipitation as the low they emanate from will dissipate over the
next day. However, that dissipating low will become an inverted
trough that the strong low to the southeast of the Gulf of Alaska
will merge into and bring in more precipitation to the north Gulf
coast this weekend. Precipitation will start off as snow but
southern parts of Prince William Sound will turn to rain and we
will need to wait and see how far the warm air can make it
westward and whether that will make it to places like Whittier and
Seward. For areas to the lee of the coastal mountains such as
Anchorage, it does look to remain mostly dry with this trough.
There is a slight chance for some snow Saturday night or Sunday,
but it would be a very brief period of snow as it typical in a
warm advection scenario like this one and then the downsloping
will kick in quickly ending and more snow. There is not great
model agreement on this low and trough, but what is discernible
is that models are all taking a farther south track than indicated
yesterday or the day before so it is possible the precipitation
stays farther south and northeasterly flow aloft would then start
to clear the area out again by Sunday or Sunday night.

&&

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

Very weak upper level flow will continue to support rather
benign conditions across most of Southwest through at least the
first half of the weekend. A large blanket of low stratus has
formed overnight across just about everywhere away from higher
terrain, although a few spots could still still see periods of
fog through this afternoon. One small region of slightly more
active conditions will be focused near a pair of upper level waves
drifting near southern portions of Bristol Bay and the northern
Alaska Peninsula (AKPen). A band of snow showers with the more
northern feature will continue to affect portions of Bristol Bay
through at least the rest of this morning, mainly to the west of
King Salmon, including Dillingham. Farther south, a slightly more
potent shortwave and an associated mesoscale low will move north
into the AKPen through this afternoon, sending light to moderate
snowfall into areas around Chignik and Port Heiden. Depending on
the exact track of this small low, Chignik could see several new
inches of snowfall accumulation through tonight before the low
dissipates.

For Saturday, continued quiet conditions are again anticipated as
weak ridging moves overhead and prevailing winds both near the
surface and aloft remain light. Offshore flow should begin to
develop and strengthen through Saturday evening, and this may
encourage any remaining low cloud cover to break up as cool, dry
air filters in from the Interior. By Sunday, forecast confidence
decreases considerably. Models are still struggling with the
handing of a low expected to move northwest into the Gulf, with
farther westward progress into the AKPen and Bristol Bay area
possible by Sunday evening. This could allow areas of snow to
spread into parts of Bristol Bay and the Lower Kuskokwim Valley
as early as Sunday evening as the low approaches the AKPen.
However, some solutions are still showing the low move much slower
and farther south, and this could allow the stretch of dry, cool
conditions to persist through at least Sunday night.

&&

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

An active but slow to progress pattern will remain in place across
the Bering for the next few days. A complex low with several
embedded smaller waves/centers will send intermittent periods of
gale force winds and a mix of rain and snow across the central and
western portions of the Chain, with the first main round of
stronger winds and heavier precipitation expected today as a North
Pacific low embedded in the broader area of cyclonic flow moves
into the southern Bering and pivots to the west towards Shemya by
tonight. The low's front will also send a quick round of rain and
snow showers across the Pribilofs early Saturday morning before
the front shears apart to the northeast. Forecast uncertainty
picks up dramatically by Saturday, with models still struggling
with the numerous embedded upper waves composing the larger,
complex low drifting over the western Bering/Aleutians. Smaller
lows will likely continue to rotate across the Aleutians and
focus smaller areas of winds up to gale force as the move past
through at least Sunday. However, the track, timing an intensity
of these  features remains highly unclear, and forecast
confidence from Saturday through Sunday night is suboptimal.

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

The long term forecast begins on Monday with an upper ridge over
western Canada, an upper trough near the western Aleutians, and a
mid-latitude low pressure system in the Pacific. Forecast
confidence is relatively low for Monday due to uncertainty in the
Mainland pattern, various northeast Pacific shortwaves, and the
flow around the mid-latitude Pacific system. There is general
consensus for the Pacific low to track south of the Aleutians on
Tuesday, although confidence in this feature decreases on
Wednesday when the Canadian and EC continue tracking east while
the GFS stalls south of the eastern Aleutians and merges with
another low from the west. Despite these discrepancies, the
Aleutians should see minimal influences from the system while the
Alaska Peninsula/Kodiak Island area could see some active weather
on Wednesday if the GFS solution wins.

The general synoptic pattern on Wednesday and Thursday will
likely be an upper trough near the western coast of the Mainland,
ridging over eastern Siberia, and a low approaching the western
Aleutians from the west. Unlike the GFS, the Canadian and EC
solutions support active weather (stronger winds and heavy
precipitation) across the Bering and Aleutians for Days 6 and 7.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray 185. Gale 175 176 173 174 177 178
179 185 411 412 413 414.
FIRE WEATHER...NONE.

&&

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