Gale Warning 62, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
553 PM AKST Thu Jan 19 2023

.ANALYSIS AND UPPER LEVELS...
The state is under a large upper level trough with the axis
extending from over the Bering Sea, across the Alaska Peninsula,
and then south of the Gulf of Alaska. This is bringing overall
warm, southerly flow aloft over Southcentral and cold air
advection across the Bering Sea. The main surface low in the east
is close to Kodiak Island this afternoon and bringing rain and
snow to Gulf coastal areas. Satellite imagery also shows another
surface low is spinning near Attu with convective snow showers
wrapped around it. Worth noting is the jet stream running in a
south-to-north orientation up the 150 meridian well to the south
of the Gulf of Alaska. This is the next system to watch and,
though the main energy from this system will head into Southeast
Alaska, it will usher in a more active weather pattern.

&&

.MODEL DISCUSSION...
Models are in reasonable synoptic agreement through the weekend.
However, as has been the case recently, the complex lows are
causing them difficulties. This is mainly impacting the areas
closer to the center of the low complex which mostly means the
Alaska Peninsula through Central Aleutians early next week.
In the shorter term, there is also some smaller embedded lows in
the North Gulf region. Hi-resolution models are indicating some
light snow overnight for Anchorage while larger scale ones such
as the GFS continue to keep the area dry. Anchorage is not the
only place affected, but this discrepancy between model types
has caused the HRRR, NamNest and others to be favored for the
next 24 to 36 hours in Southcentral.

&&

.AVIATION...
PANC...A marginally stronger short-wave trough will approach
Anchorage from the Gulf this evening. While there is some
southeasterly flow coming across the mountains, it doesn't look
strong enough to inhibit precipitation. It's hard to nail down
the exact timing of precipitation, but generally expect periods of
light snow late this afternoon through evening, with MVFR
conditions. There is a chance of IFR conditions if snow comes in
heavier than expected, but it would be very brief. Ceilings will
quickly lift behind the short-wave overnight, with VFR conditions
then persisting through Friday.

&&

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

An elongated trough continues to swing over the Gulf this evening
with multiple shortwaves embedded within. These shortwaves have
been traversing through the area and have caused precipitation
along coastal areas this evening. A band of snow is likely to
develop and track northward towards Anchorage this evening into
tonight. Accumulations with this band will be relatively light
with only a coating to around an inch or so of snow expected.
Tonight through Friday morning, winds will be more southeasterly
and areas along the Gulf coast and through Turnagain Arm could see
a mix of rain and snow and then turn to all snow for Friday night.
Uncertainty rises in relation to what type of precipitation will
fall due to the variability on when the warmer air will move into
those areas and stay. A North Pacific low will track into the Gulf
Friday into Saturday accompanied by gale force winds wrapping
around the aforementioned low's center. Precipitation will remain
mainly along the coast. The exception will be the Copper River
Basin as snow will work its way into the basin late Friday evening
through Friday night. Accumulations are expected to stay relatively
light and any higher accumulations should remain confined to
mountain areas. By the end of the weekend, winds will become more
northerly across the forecast area and will trend temperatures
cooler.

&&

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

An upper-level trough with embedded shortwaves will maintain
light snow showers across portions of Southwest Alaska through
Saturday morning. An upper ridge from the Bering Sea will follow
in the wake of the trough and build across the domain, resulting
in dry and clear conditions for the Southwest on Saturday. Clouds
and precipitation return to the Alaska Peninsula starting Saturday
night as a North Pacific low extends its front to the north Gulf
coast. By Sunday afternoon, clouds and increased chances for snow
will spread north into the Southwest mainland, where precipitation
should be lighter and showery in nature. The Alaska Peninsula,
however, can expect to see the heaviest (and steady) snowfall with
this system, especially on the Pacific side due to northeasterly
flow.

Strong northerly cold air advection preceding the ridge will
maintain elevated winds across the Kuskokwim Delta, Bristol Bay,
and Alaska Peninsula tonight into Saturday. Later Saturday
morning, winds will shift northeasterly as the ridge exits to the
northeast and a large North Pacific low lifts into the Bering.
This resulting offshore flow will be quite strong across the
Kuskokwim Delta and Bristol Bay area through Sunday, so the
possibility for winds transporting already existing snow is not
out of the question. In general, cold air combined with stronger
winds will continue to promote very cold apparent temperature
values for the Kuskokwim Delta through Sunday.

&&

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

The Bering Sea and Aleutians can expect to see continued active
weather through the short-term forecast. A front currently over
the Western and Southern Bering will weaken through Friday morning
as a compact North Pacific low tracks across the Central Aleutians.
The low will will exit the Western Bering towards Russia on
Saturday morning, with its occluded front lingering over the
Western Bering. With this system, expect rain and/or mixed
precipitation and sustained winds up to storm-force across much of
the western and central domain. A second North Pacific low (this
one still looking stronger than the first) is advertised to lift
north to the Aleutian Chain on Saturday afternoon. Expect rain to
blanket the Chain and Southern Bering on Sunday, as well as strong
winds with gusts up to hurricane-force for the Eastern Aleutians
(likely between Adak and Dutch Harbor on Saturday).

&&.

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

The overall pattern in the extended range continues to be
difficult to resolve, with even some of the larger scale players
in the pattern evolution shifting around considerably in terms of
the run-to-run continuity. One of the biggest changes is that
newer model runs from today are no longer showing the Arctic low
near Siberia moving as far south as it heads towards northern
Alaska over the weekend, resulting in a very different looking
setup across the Bering and Southwest at the start of the extended
period on Monday. Most solutions now keep the low and most of the
bitterly cold Arctic air well removed from the outlook area over
the Interior and North Slope, with the projections showing the low
stretching out to the south and allowing very cold air to spread
into the eastern Bering and Southwest losing support. The lack of
cold, dense air and higher pressure developing across the same
region has resulted in a big shift for the track of a large area
of low pressure expected to move past the Aleutians into the
southern Bering early next week. The consensus from 12z guidance
has shifted the low track significantly north, now showing the low
and a deep upper trough lifting well into the Bering on Monday
and Tuesday rather than staying along or south of the Aleutian
Chain.

The potential for precipitation east of the low extending across
Southwest and Southcentral has shifted notably north as well, with
much higher potential for interior parts of the southern Mainland
to see periods of snow or even rain as deep, southerly flow
pushes warm air and multiple shortwaves inland from the Gulf
through midweek. All of the large, wild shifts in even the broader
scale pattern make it nearly impossible to hash out details for
individual systems, but it does look like a clear tilt towards a
warmer/wetter period for much of next week. There is also an
emerging signal for a very potent low to enter the far western
Bering by Thursday, possibly impacting the western fringes of the
Aleutians/Bering with storm force winds, and perhaps even stronger.
The GFS is by far the most bullish with this scenario, currently
depicting a 930-940 mb Hurricane force low move west of Attu by
Thursday afternoon. The ECMWF/Canadian are much weaker with this
system and are showing the low move much farther west.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray Warning 160 179 180 185.
         Storm Warning 178.
         Gale Warning 119 130 131 132 150 170 172
                      173 174 175 176 177 185.
FIRE WEATHER...NONE.

&&

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