Gale Warning 669, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
1128 AM AKST Sun Nov 5 2023

.Update...

The upper low and associated trough axis has been slow to pivot
before dropping southward this morning, and the upper low is just
now starting to move into the Kamishak Bay area. This has
resulted in a more prolonged period of moderate snowfall this
morning for much of the Turnagain Arm/western Chugach Mountains,
Anchorage Bowl, and Susitna Valley. Current satellite imagery (as
of 20Z) show the back edge of the heavier snowfall to be north of
Kenai and starting to near the Turnagain Arm. The Anchorage Bowl
up through the Susitna Valley may see another hour or two of
periodic moderate snow, but it looks like most of the heavier
snowfall is starting to wind for these areas. However, light snow
or flurries will likely linger through the afternoon and into the
evening hours for these locations.

&&

.PREV DISCUSSION... /issued 529 AM AKST Sun Nov 5 2023/

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

An upper level low is positioned over interior Bristol Bay this
morning, with a trough digging southeastward across the western
Gulf and into the northeast Pacific. A short-wave tracking
underneath the low this morning has slowed the progression of the
low along the trough axis. As a result, there has been a change in
the synoptic solution for the second day in a row, with the
lingering upper level low leading to heavier precipitation out
ahead of it. As a result, after having trended lower with the snow
accumulation forecast yesterday, have now trended back to closer
to the original forecast amounts.

A band of steady precipitation extends from western Prince
William Sound northwestward across the northern Kenai Peninsula to
Anchorage and the southern Susitna Valley. Colder air has moved
up Cook Inlet changing precipitation to all snow. Rain continues
just north of Anchorage and across most of the eastern Kenai
Peninsula, but cold air will continue to advect north and east
changing precipitation to all snow for these areas.

The band of precipitation will continue to track very slowly
north and east this morning as the low moves into the
northwestern Gulf. As the low continues southeastward into the
Gulf this afternoon and evening, precipitation will diminish.
However, the remaining weak trough will continue to progress
northeastward, so areas of very light snow will linger. One area
to keep an eye on will be Cook Inlet where low level convergence
could lead to a very narrow band of snow somewhere along the
western Kenai and Kachemak Bay coasts. These have been known to
cause very localized snow accumulation.

As we head to Monday the original trough will continue a slow
march northeastward across Southcentral. Meanwhile, a new long-
wave trough over the Bering Sea will quickly make its way toward
Southcentral, with a plethora of short-waves tracking rapidly
eastward in the fast flow aloft. Models typically struggle with
the track and strength of these short-waves in progressive flow,
so don't put a whole lot of faith in the precipitation guidance.
This will be favorable for areas of light precipitation, primarily
in the form of snow, Monday through Monday night.

The upper trough will amplify on Tuesday, leading to development
of a large and deep surface low somewhere south of Kodiak Island.
Rapidly building heights downstream will cause the storm system
to lift northward Tuesday night/Wednesday. This will be the most
significant storm to affect the region in quite some time, with
widespread winds and heavy precipitation impacting the Gulf coast
and some of this likely spreading inland across Southcentral.
There is uncertainty in the details of this system, but high
confidence that it will be impactful.

SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Tuesday night)...

No major changes to the short term forecast as a large mid/upper
level trough extends from the northwest coast of Alaska down
through the Alaska Peninsula this morning, with a deepening
parent low near St. Matthew Island and associated frontal system
draped across the central Aleutians.

Isolated light snow continues across the Kuskokwim Delta through
Bristol Bay this morning as minor mid/upper lvl disturbances work
around the periphery of the trough. The developing St. Matthew
low pressure system will keep an active weather pattern for much
of SW AK into the Aleutian Chain through the short term and into
mid week. Some model discrepancy at this time in regards to storm
track but general consensus is that low pressure system will
gradually deepen and move SE towards the Pribilof Islands through
early next week. As the system moves east and winds turn more SW-
ly, expecting warmer air to push into coastal portions of SW AK,
with high temperatures reaching above freezing from King Salmon
and areas south down the AK Peninsula by Monday into Tuesday. As
this warmer air pushes inland, anticipating a temperature gradient
and resultant rain to rain/snow to snow transition. With the
warmer Pacific air, expecting light rain to a rain/snow mix along
coastal areas with a change to all snow the farther inland and
north you go.

LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...

An deep upper-level low located over the Gulf of Alaska will
anchor a negatively tilted longwave trough that will extend from
Eastern Siberia south and east into the Northern Pacific. This
trough will serve as a conveyor belt for surface lows to move
through Southern Alaska through the next work week and into next
weekend. Several lows will track from the western Bering creating
wet and windy conditions across the Bering and into Southwest
Alaska. As one such low approaches the northern Gulf coast
Wednesday with gale-force winds while another gale force low in
the Central Bering another round of wet and windy conditions
along the Aleutian Chain. There is the potential for both of these
systems to produce storm-force winds if the appropriate barrier
jet or cold air advection sets up. While Southwest and the
Aleutians will likely see a series of periodic downpours, while
Southcentral, largely the Southcentral coastline, is expected to
see persistent moderate to heavy precipitation. The type of
precipitation associated with this system will likely be rain
along the coast, however further inland may see a transition to
snow as cold air moves wraps into the storm system. Timing of
these waves and impacts to typically sheltered areas such as
Anchorage are still in flux as models continue to resolve the
progression of the trough and individual waves. Stay tuned as
Winter makes arrives in earnest in Southcentral.

CC

AVIATION...

PANC...Southerly winds and snow will keep conditions between MVFR
and IFR through approximately 21Z this morning before it lightens
up and clouds begin to lift to predominantly MVFR. There is some
uncertainty in how long snow will continue, but anything past ~2Z
today should be very light with ceilings between 3000ft and
5000ft.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
112 PM AKST Sun Nov 5 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1040 AM     Snow             7 S Anchorage           61.11N 149.86W
11/05/2023  M4.0 inch        Anchorage          AK   Public

            Snowing at time of observation.

&&

PP

Preliminary Local Storm Report
National Weather Service Anchorage AK
113 PM AKST Sun Nov 5 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1051 AM     Snow             Tudor Rd and Seward Hwy 61.18N 149.86W
11/05/2023  E3.0 inch        Anchorage          AK   Public

&&

PP

Preliminary Local Storm Report
National Weather Service Anchorage AK
115 PM AKST Sun Nov 5 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1057 AM     Snow             null                    61.15N 149.82W
11/05/2023  E4.0 inch        Anchorage          AK   Public

            Heavy, wet snow.

&&

PP

Preliminary Local Storm Report
National Weather Service Anchorage AK
117 PM AKST Sun Nov 5 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1113 AM     Snow             11 SE Anchorage         61.07N 149.77W
11/05/2023  M6.0 inch        Anchorage          AK   Public

            Updated snowfall total.

&&

PP

Preliminary Local Storm Report
National Weather Service Anchorage AK
118 PM AKST Sun Nov 5 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1124 AM     Snow             5 SW Anchorage          61.15N 149.93W
11/05/2023  M5.1 inch        Anchorage          AK   Public

            Corrects previous snow report from null.
            Near Birch Lake.

&&

PP

Preliminary Local Storm Report
National Weather Service Anchorage AK
119 PM AKST Sun Nov 5 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1247 PM     Snow             Spenard                 61.18N 149.93W
11/05/2023  E3.0 inch        Anchorage          AK   Public

            Near Jefferson and Northwood Dr.

&&

PP