Brisk Wind Advisory 85, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
537 AM AKST Tue Dec 27 2022

.ANALYSIS AND UPPER LEVELS...

A surface low is situated south of Seward and will weaken through
tonight, dissipating by Wednesday morning. Winds have diminished
for most areas and precipitation has tapered out across Anchorage
and the Mat Valley. There remains some light snow across the
southern portions of the Kenai Peninsula, shown on Radar
overnight, and Valdez. There is some wrap around colder air
pushing into Southcentral and winds aloft are shifting
southeasterly.

A separate low exists out west over the Western Aleutians that
will shift into the north Pacific over the next few days, pulled
southward by yet another low developing in the north Pacific that
is approaching the southern Alaska Peninsula. An elongated trough
extends into the southern Gulf of Alaska. The low looks to stall
briefly south of Unalaska on Wednesday before moving north.
Discrepancies amongst models increases as the low shift track. How
far north the low ends up will be the determining factor for
precipitation in the Pribilof Islands.

By Wednesday night, a second north Pacific low develops in the
base of the trough and pushes north towards the north Gulf coast
through Thursday night, bringing active weather back to the
region.

&&

.MODEL DISCUSSION...

There is better model agreement with the north Pacific low moving
towards the southern Alaska Peninsula over the next few days.
Since yesterday, models have trended more towards what the
Canadian has been showing, with the low stalling briefly south of
Unalaska on Wednesday. Model spread grows significantly by
Thursday, the biggest inconsistency being how far north the low
travels. The main challenge with that is in the precipitation
forecast for the Pribilof Islands. The forecast challenge on the
east side is chance for more freezing rain possibilities across
Anchorage and the Kenai Peninsula this morning as a series of
shortwaves move across the area.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. There is a
chance for periods of light freezing drizzle in the morning,
and a chance for very light snow in the afternoon. Additionally,
cloud ceilings will drop below 5000 feet in the afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 2: This
morning through Wednesday afternoon)...

An upper level trough in place over the northern Gulf is
lifting multiple rounds of upper level waves from south to north
across Southcentral. The associated surface low currently centered
south of the Kenai Peninsula will gradually track northeastward
today toward Prince William Sound. One change to the forecast is
a slightly more southerly track than previously advertised,
however by Wednesday, this low still looks to lift northward
(inland) and dissipate. The bulk of the precipitation between now
and Wednesday is still expected to fall along coastal locations -
especially eastern Kenai Peninsula, Prince William Sound, and the
northern Gulf coast including Valdez and Cordova.

The biggest challenge this morning is precipitation type,
especially along the western Kenai Peninsula, Anchorage Bowl, and
Matanuska Valley. A warm layer still remains near 1,000-1,500 feet
above the ground this morning. As moisture associated with the
Gulf low moves from east to west, there is a chance for freezing
drizzle to develop over the Anchorage Bowl and Matanuska Valley
this morning. Meanwhile the western Kenai Peninsula has seen a mix
of precipitation overnight, and surface observations for Homer in
particular have been indicating periods of freezing rain mixed
with snow.

As this low continues to weaken, colder air will wrap around and
any lingering precipitation should change to snow, with the
exception of warmer locations along the coast. Additionally, an
upper level wave arriving over the southern Susitna Valley
this afternoon may help to enhance snowfall tonight, particularly
west of the Parks Highway along the foothills of the Alaska
Range.

By Wednesday afternoon, attention shifts to a North Pacific low
lifting northward toward Southcentral bringing a relatively warmer
airmass, and another chance for precipitation.

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

Light snow will continue for the Bristol Bay region tonight into
Tuesday morning as a front lifts northward across Southwest
Alaska. A shortwave ridge will build into the region today,
bringing clearer and drier conditions. Offshore flow will return
tonight as a deep North Pacific low approaches the southern
Alaska Peninsula. This, in combination with clearer skies, will
help aide in making temperatures colder tonight with overall nighttime
lows in the single positive digits and single negative digits for
the Kuskokwim Valley. However, this will be short-lived as
another front approaches the region for Wednesday associated with
the aforementioned North Pacific low. Easterly flow will develop
across Southwest Alaska Wednesday morning, causing a quick rise in
temperatures into the mid 20s and 30s for Bristol Bay region and
in the lee side of mountain areas. Models are having a hard time
resolving the evolution of this system and how it will impact the
region into the weekend. Be sure to check back with the forecast
as further refinements are made.

&&

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

An upper-level low will continue to track southward across the
western and central Aleutians through Wednesday as cold air and
snow showers stream southward across the Bering Sea. The
aforementioned low will help bring a North Pacific low up to the
eastern Aleutians and southern portion of the Alaska Peninsula
late today. Warmer air and moderate to strong easterly winds will
accompany the aforementioned low through Wednesday. This feature
becomes the dominant low as the upper-level trough elongates
along the Aleutian Chain. Wednesday night, uncertainty increases
as to whether the low tracks across the Chain and into the Bering
or if it remains over the North Pacific. The positioning of this
low will determine where the heaviest precipitation will be, where
blowing snow could occur, and where the strongest winds will be.
Be sure to check back with the forecast as further refinements and
updates are made.

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

The latest operational models and ensemble means are in fairly
decent agreement with an upper closed low over the eastern
Aleutians and Alaska Peninsula. While the upper low sits nearly
stationary over the weekend, a strong North Pacific low rotates
around the low, moving northeastward past the Aleutians and into
the Gulf of Alaska. This will bring an unsettled pattern for all
of the coastal areas of Southcentral heading into early next week.
While specific details still need to ironed out, persistent
onshore flow will favor moderate to heavy precipitation for the
coast, while much of the mainland will be relatively dry during
the period. For Southwest AK, precipitation looks to be favorable
for the AKPEN, while much of the inland areas will be downsloped
due to the southeasterly flow. A general troughing pattern out
west will result in a wet pattern for much of the Bering Sea and
Aleutians. Cold, northerly flow over the relatively warm waters
will also help generate widespread showers over the Pribilof
Islands and along the Aleutian Chain.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 131
MARINE...Gale Warning: 155 165 170 172
		 Heavy Freezing Spray Warning: 160 180 181 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...MF