Gale Warning 863, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
420 PM AKST Fri Dec 30 2022

.ANALYSIS AND UPPER LEVELS...

A long-wave trough remains firmly entrenched across Alaska and the
North Pacific, with a complex series of lows and short-waves rotating
around the anchor low along the Aleutians. For today, there are
mostly weak features across the forecast area producing low impact
weather. A short-wave lifting northward across southern Alaska is
leading to widespread cloud cover and areas of light snow, except
areas at sea level along the north Gulf coast/Prince William Sound
where it is just warm enough to fall as rain. A weak vertically
stacked low south of Kodiak Island and the Alaska Peninsula is
lifting slowly northward, with rain spreading northward across
Kodiak Island and snow spreading across the Alaska Peninsula in
the vicinity of Port Heiden. A short-wave tracking southward
across the Bering Sea is focusing snow showers and gusty northerly
winds across the central to western Aleutians.

Meanwhile, further south over the North Pacific, a buckle has
developed in what had been a zonal subtropical jet stream. A new
low keeps forming along this buckle in the jet, leading to a
strung out series of multiple low centers. This low complex is
tracking east-northeast toward the Alaska Peninsula, Kodiak Island
and the Gulf of Alaska. Further amplification of the flow is
leading to development of an atmospheric river. These is the set-
up for what will be the next significant storm to affect southern
Alaska in the coming days.

&&

.MODEL DISCUSSION...

Model guidance has a decent handle on current features, but
continues to struggle mightily with the complex series of lows
crossing the Gulf of Alaska the next couple days and progression
of the leading occluded front onshore of Southcentral. This is
no surprise as models typically struggle with this pattern of
numerous short-waves rotating around a single large center. This
does make it quite a challenge to hone in on the details of the
wind and precipitation forecast. However, based on the pattern,
strength of dynamics, and presence of an atmospheric river, we
are able to highlight some likely impacts across the region.
Today's forecast changes attempt to depict the general expected
weather across the forecast area while advisory/watch/warning
products and social media highlight most likely impacts and
areas of uncertainty.

&&

.AVIATION...
PANC...Flurries remain a possibility this afternoon/evening as
a weak short-wave passes overhead. However, VFR conditions and
light winds will persist.

&&

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

A very active weather pattern is expected for this weekend as a
storm system moves in from the North Pacific. This storm will
bring strong winds and a mix of wintry precipitation across
Southcentral. Widespread precipitation will move across the area
Saturday evening and night. Precipitation is expected to begin as
snow across Southcentral with the exception of immediate coastal
areas along Kodiak Island, southern Kenai Peninsula and Prince
William Sound as temperatures will be warmer in those locations.
Warmer air will move northward overnight and thus result in a mix
of wintry precipitation, specifically snow and freezing rain. Snow
is likely to begin mixing with freezing rain after 3am AKST across
the Anchorage Bowl, Matanuska Valley, western Kenai Peninsula and
in the Susitna Valley south of Talkeetna. Temperatures aloft will
continue rising and this will allow for the mix of snow and
freezing rain to transition to all freezing rain across the
Anchorage Bowl, Matanuska Valley, western Kenai Peninsula and the
lower elevations of the Copper Basin south of Copper Center midday
Sunday. Freezing rain and a mix of snow and freezing rain will
continue through those aforementioned locations until midday
Monday before turning back to all snow.

The other story is the strong winds as widespread gale force winds
with areas of storm force winds are expected in the Gulf of
Alaska. A Turnagain Arm wind is expected Saturday night through
Monday. Pressure gradients support this Turnagain Arm wind bending
down-inlet and away from Anchorage.

&&

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

An elongated trough of low pressure situated over the Bering Sea
continues to be the main weather driver for Southwest Alaska. A
weakening low located south of the eastern Aleutians will bring
another round of light precipitation along the Alaska Peninsula
(AKPEN) and northward into coastal Bristol Bay. A band of rain
showers will be south of King Salmon, while snow showers will
push north and west of Dillingham tonight and taper off sometime
Saturday afternoon. The rest of the mainland will be relatively
dry due to downsloping southeasterly flow.

Heading into the Holiday weekend, attention turns to a stronger
low pressure system tracking across the AKPEN and into the eastern
Bering Sea. There is quite a bit uncertainty in the track of this
storm, so exact timing and amount of precipitation could change.
Depending on the exact track of the aforementioned low,
increasing easterly winds will coincide with light to
occasionally moderate snow showers across the region. This will
promote a threat for blowing snow and potentially reduce
visibility from late Saturday to Sunday across Bristol Bay. The
forecast package continues to be updated, including potential
impacts encompassing from Naknek to Dillingham to Koliganek. As
the low stalls out over the eastern Bering, unsettled conditions
continues well into early next week. Stay tuned for any
adjustments as the situation develops.

&&

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

An elongated trough of low pressure situated over the Bering Sea
continues to be the main weather driver. Widespread east to
northeast small craft winds with some pockets of gales will be
over the northern and western Bering throughout the Holiday
weekend. These winds will also slowly expand into the eastern
Bering/Aleutians as a strong low tracks across the Alaska
Peninsula. By Sunday, a broad swath of northerly small craft winds
will blanket the Bering from Saint Matthew Island into the
Aleutian Chain, with seas of 8 to 12 feet expected.

Cold, northerly flow over the relatively warm waters will also
help generate widespread showers over the western Bering and
Aleutians. Any shower activity across the eastern Aleutians is
expected to fall as rain through Saturday while snow will be
possible further west into early next week.

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

Going into the long term, the low forecast to bring this
weekend's active weather to southern mainland Alaska will have
weakened significantly, elongating along the Southwest coast and
across the Alaska Peninsula on Tuesday. By that point, mainly
only upslope precipitation will be lingering along the Gulf coast
as southerly flow continues to wrap around the weakening low.
Scattered, showery precipitation may also continue to be present
in Bristol Bay and along the Alaska Peninsula in the vicinity of
the decaying low. Any precipitation is likely to be all snow.
Elsewhere, inland locations will be mostly dry. Beyond Tuesday,
uncertainty increases, with large spread in the timing and track
of various features. One of the higher confidence features is a
potentially gale-force low entering the eastern Gulf of Alaska
Tuesday night and tracking toward the western Gulf coast by
Wednesday night. Several other lows look to take a similar track
following this one, however, models disagree on where the energy
is focused, meaning the strength of this feature is highly
uncertain. Its impacts, primarily another round of coastal
precipitation, are most likely to be focused between Kodiak
Island and the eastern Kenai Peninsula Wednesday into Wednesday
night. Some light overrunning precipitation may move into the
Cook Inlet region and Southwest Alaska, but it is likely to be all
snow. As the low weakens into Thursday, southern mainland Alaska
looks to dry out with weak flow and no major source of moisture
available, though some upslope shower activity may continue along
the coastal mountains.

Out west, northerly flow prevails across the central and eastern
Bering Sea at the beginning of the period, with scattered snow
showers moving into the Aleutians. In the western Bering, a large
upper-level low supported by a cold air mass moving out of East
Asia begins to encroach. It is led by a front, which appears to
bring mostly snow to the western and central Aleutians through
Tuesday night. The Pacific jet will retain a primarily zonal
orientation far south of the forecast area, meaning that as the
upper low slowly moves over the Bering/Aleutians, it will bring
with it many embedded hard to resolve, weak-to-moderate intensity
lows. This will keep relatively cold air in place and bring
periodic chances for snow reaching as far east as the eastern
Bering/Aleutians by Friday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WATCH 125
         WINTER WEATHER ADVISORY 101 111 121 141 145
MARINE...STORM WARNING 119 120 130 131 138 139.
         GALE WARNING 125 132 136 137 140 150 160 178 351 352 411.
         HEAVY FREEZING SPRAY 180 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...ED
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
LONG TERM...CQ