Small Craft Advisory 25, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 AM AKST Sat Jan 7 2023

.ANALYSIS AND UPPER LEVELS...

A longwave trough extends from the Bering to North Pacific with
the jet core continuing to remain south of the Aleutian chain near
36 latitude. The jet core has an estimated magnitude of 16 knots.
At 500mb and 700 mb there is an an inordinate amount of
shortwaves spanning from Kamchatka to the Gulf Of Alaska. On
satellite imagery, there are a pair of back to back fronts over
the Western and Central Aleutians. Rain and gusty conditions were
detected from Atka to Dutch, while a mix of rain and snow is being
seen through Shemya. Inversions keep setting up over Southcentral
and Southwest Alaska. Early this morning, on the "Nighttime
Microphysics" there is a patch of fog/low stratus over portions of
Cook Inlet.

&&

.MODEL DISCUSSION...

The models continue to struggle with the placement of the surface
lows early in the forecast period. These discrepancies amplify
with time. Generally speaking at the synoptic scale, the models
show the longwave trough residing over the Bering and into the
North Pacific. The models all show the lows over the Western and
Central Bering and the inverted trough that is moving up towards
the Gulf Of Alaska.

&&

.AVIATION...

PANC...On nighttime microphysics imagery there is some fog/low
stratus near PANC. It is actively being monitored. Absent fog,
expect VFR conditions and light winds will persist. Amendments
will be made as needed.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3/Today through Monday)...

Areas of fog will continue over Cook Inlet and parts of the
western Kenai Peninsula through today and may expand across Cook
Inlet tonight. However, drier air has advected into Anchorage and
the Mat-Su valleys which has kept this area mostly clear and fog
free except patchy areas of fog are possible over the Knik River
through today. Areas of fog will continue across the Copper River
Basin today and may briefly lift for a few hours this afternoon
before redeveloping tonight.

Models have come into a bit better agreement with a shortwave
moving towards the northern Gulf which is supporting an inverted
trough at the surface. This feature will spread snow across Prince
William Sound and southern parts of the Copper River Basin late
Saturday and into Sunday. The GFS is the fastest at bringing this
inverted trough towards the eastern Kenai Peninsula and northward
on Sunday, but has trended slower and is closer to most other
models on the latest model run. Thus confidence has increased in
the wind and precipitation forecast through Sunday with this
feature. Light snow is expected to move across the Chugach
mountains and into the Anchorage and Mat-Su valleys on Sunday with
light snowfall accumulations possible of an inch or two. However,
it is difficult at this point to pinpoint the exact timing of
this snowfall as there are differences in the models moving the
precipitation eastward. Some models suggest a brief period of snow
Sunday morning and then another period of snow Sunday afternoon
and evening.

Another stronger low pressure system will move from the north
Pacific into the southern Gulf and Kodiak Island on Sunday into
Monday bringing rain and snow to Kodiak Island and southern parts
of the Kenai Peninsula. However, there is quite a bit of model
spread on the movement and position of this system so forecast
confidence is low on the timing of the precipitation. But we have
high confidence that this low pressure system will bring
precipitation to Kodiak Island and the Kenai Peninsula Sunday or
Monday. Stay tuned...

&&

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

The pattern will remain quiet for the next day or so before the
next system begins to encroach on at least the eastern portions of
the outlook area at the start of next week. In the near term
through tonight, areas of low stratus and patchy fog will hold on
through much of the day today over valleys as a weak upper ridge
initially remains in place. A few light snow showers or flurries
are possible in the vicinity of Dillingham and Togiak this morning
near a weak upper shortwave, but this activity should end by this
afternoon as the trough axis shifts northeast. Most of the low
stratus deck in place should start to mix out by tonight as drier,
offshore flow develops out ahead of a low and inverted trough
axis approaching the Alaska Peninsula (AKPen) from the east.

Looking out into Sunday and beyond, the forecast details are still
fairly uncertain as the low moving west across the Gulf approaches
and perhaps eventually crosses the AKPen into the eastern Bering
Sea by Monday. There is still quite a bit of model spread in the
progression of the low towards the northwest, resulting in timing
differences for bands of mostly light precipitation expected to
expand into the Middle Kuskokwim Valley and Bristol Bay from the
east between Sunday evening and Monday morning. Light snow could
eventually work its way all the way up to the Kuskokwim Delta late
on Monday, depending on how far and how quickly the low is able to
advance into the AKPen/Bering. There may be enough warm air
advecting past the Alaska/Aleutian Ranges north of the low to
allow for snow to mix with rain across parts of Bristol Bay on
Monday. However, even with the outlined uncertainty, it appears
likely rain and snow will stay rather light and intermittent for
most areas through Monday evening.

&&

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

A broad area of low pressure with a myriad of embedded centers
rotating around one another will continue to impact much of the
western Bering and central/western Aleutians through Sunday. One
of the stronger gale force lows is now lifting north of Adak and
Atka, with it's front pushing a band of rain and snow towards
Nikolski. By this afternoon and evening, another compact low is
expected to cross into the Bering from the southeast, briefly
vaulting winds up to gale force along the central Aleutians along
with bringing a period of moderate rain to areas between Atka and
Nikolski. As this next center continues northwest into the Bering
on Sunday, it should weaken along with the broader upper low as
the entire circulation shifts northwest and begins to fill in.
This should give way to calmer conditions for Monday, with calmer
winds along the Chain and little precipitation aside from widely
scattered snow and rain showers.

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

Key features in the long term include an upper level trough over
the western half of the state Tuesday morning. This will quickly
lift northward, generating snow showers across the Kuskokwim Delta
Coast. On the eastern side of this feature, several upper level
waves over the Gulf will lift northward over Southcentral,
introducing the possibility for precipitation, especially for
areas along the coast. Meanwhile the more significant feature of
note is a broad upper level low that moves from the North Pacific
into the Bering on Wednesday. Models have been far more
consistent with this feature, and are advertising a fairly deep
and broad low to impact the Bering and Aleutians Wednesday into
Thursday. If this pans out, would expect widespread precipitation
and gusty winds, especially along the Chain. Farther east during
this time, a broad upper level ridge over the Alaska- Yukon border
seeks to build across the mainland along an axis oriented from
southeast to northwest. This would introduce generally fair and
calm conditions for Southcentral. Currently, this pattern is looking
fairly progressive. By Friday, the Bering low will lift
northward, allowing several additional upper level shortwaves to
traverse south to north across the Bering and over the Southwest
Alaska coast by next weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray 180 185. Gale 352 130 132 138 139
172 173 174 178 185 412 413.
FIRE WEATHER...NONE.

&&

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