Gale Warning 723, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
847 AM AKST Sun Nov 13 2022

.ANALYSIS AND UPPER LEVELS...

A closed upper high exists over the northern Bering with a broad
trough to it's south extending from the Kamchatka Peninsula south
to 40N and then due north into Southcentral. Multiple embedded
shortwaves exist within the trough, with the most notable features
being a low over Bristol Bay and a developing low in the North
Pacific south of Kodiak Island. Southerly winds/gap winds
throughout Southcentral have kept overnight temperatures in the
mid 30s to mid 40s despite areas of clear skies. On radar a broad
precipitation shield from the low south of Kodiak has reached the
Gulf Coast. Over Southwest, northerly flow from Togiak north and
west has kept temperatures cold, with wind chill over the
Kuskokwim Delta between -5 and 5 degrees Fahrenheit. Over the
Bering, cold air streaming south through the Bering Strait has
lead to cloud streets and below freezing temperatures for the
Pribilof Islands.

&&

.MODEL DISCUSSION...

Models are in moderate agreement in the short term but continue to
have differences in timing and speed of propagation of a north
Pacific low that is expected to move up the Cook Inlet and into
the Interior this afternoon and into the evening. Upon model
initialization, a narrow low with two centers develops near 50N,
with the faster solutions developing the northern low into the
dominant system and the slower solutions developing the southern
solutions into the dominant system. Overall the models have a
similar overall storm system/structure, but the timing of certain
impacts such as wind and precipitation varies by up to 5 hours
depending on the solution. Out west, models have finally locked in
on a solution for the Bristol Bay low with high confidence the
low will dissipate in place rather than moving inland. After the
Southcentral low, model agreement is good with high confidence of
warmer conditions persisting and a general drying trend for the
Southern Mainland as the northern Bering high shifts east.

&&

.AVIATION...

PANC...VFR conditions will likely persist through the daytime
hours with flow aloft keeping the area downsloped. Turnagain Arm
winds are expected to weaken through the morning before becoming
northerly as a North Pacific low moves South of the Kenai
Peninsula and pulls winds down the inlet through the late
afternoon to evening hours. The low is then expected to pass over
the terminal as it moves north, which will bring a period of
strong southerly winds, rain and MVFR ceilings this evening.
During a short period of time just after the low passes overhead
gusts in the 30 to 35kt range are possible. There is some
uncertainty in the wind forecast in regards to timings and
strength, particularly between 0Z and 6Z as the low moves through.
After the low passes winds will remain southerly while slowly
diminishing.

&&

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

A low just to the south of Kodiak Island this morning will deepen
slightly as it takes a due north track up to the western Kenai Peninsula
midday then inland across the Susitna Valley late this afternoon.
There is some uncertainty in the speed of the low, but confidence
in the track and expected weather is higher. It's important to
note the environment this storm is moving into. As per the 12Z
Anchorage, aside from a shallow inversion near the surface, the
lower levels are well mixed and warm, with a freezing level over
3000 feet. This is quite representative of Southcentral as a
whole, where gusty winds overnight have maintained above freezing
temperatures across much of the region. While pressure gradients
will flip this morning in the Cook Inlet-Susitna Valley corridor,
causing a shift to northerly winds, there will be little change in
the overall environment. Meanwhile, warmer air and strong winds
will move in with the system. As a result, this will be primarily
a rain event for lower elevations of Southcentral.

With an overall fast movement of the low, weather conditions will
be fast changing through the day. The low does look a little
deeper than the previous forecast, so have strengthened winds
across the board, but especially over the northern Gulf and into
the Prince William Sound region. Winds will be further enhanced
through bays and passes and up in the mountains. Precipitation
will be heavy at times, but generally won't be long-lived in any
one location due to the fast northward progression of the low.
Lower elevations of Anchorage and the Mat Valley will largely be
downsloped due to very string low level southeasterly flow ahead
of the low. However, the approach of an upper level short-wave in
due south flow aloft combined with deep moisture transport from
the Pacific, can't completely rule out some light rain this
afternoon. As the low heads inland late this afternoon and
evening, downslope flow will end. Cold air advection induced
instability combined with some weak upper level waves will cause
showers to linger. With persistent strong low level flow, steadier
precipitation will persist tonight in the Susitna Valley and
eastern Prince William Sound (Valdez/Cordova area). Once again,
gusty winds will tend to maintain elevated temperatures. So
despite the cold air advection, the predominant precipitation-
type for areas at sea level will remain rain.

While the storm exits to the Alaska Interior tonight, upper level
cyclonic flow will persist through Monday, with precipitation
lingering in the aforementioned upslope areas. Still, expect most
of the region to dry out on Monday and winds to diminish. High
pressure will then build over mainland Alaska Monday night through
Tuesday, leading to offshore flow and cooling temperatures. A
warm front extending from a deep low over the Pacific will lift
north and west across the Gulf of Alaska Monday night through
Tuesday night. The front looks pretty weak, so winds and
precipitation with this are highly unimpressive. Most likely this
will produce a brief period of rain for Kodiak Island. Some
precipitation could reach the Kenai Peninsula, depending on the
position of the ridge. With warming temperatures aloft, expect
strengthening temperature inversions over Southcentral and
increased chance for fog as we continue through the week.

&&

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

Morning satellite reveals a weak trough of low pressure remains
just offshore of Bristol Bay. Areas of rain and snow continue lift
northward across Southwest as a result. Temperatures have been
warm enough from King Salmon to Iliamna to maintain rain while
snow has been observed from Dillingham to Bethel to Aniak. Light
precipitation chances will linger through tonight before gradually
tapering off by Monday afternoon as low pressure over Bristol Bay
fills in and dissipates. Meaningful snow accumulations are not
anticipated. Finally, as high pressure over the Bering eventually
slides into Central Alaska by Tuesday, precipitation chances for
Southwest should come to an end.

&&

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

A longwave ridge of high pressure continues over much of the
Bering Sea with a persistent weak trough of low pressure remaining
offshore of Bristol Bay. Between these two features a belt of
northeasterly small craft and gale force winds will continue to
stream over the YK Delta, across Nunivak Island, and into the
Pribilof Islands through tonight. Winds are forecast to diminish
later on Monday as the low over Bristol Bay fills in and
dissipates. Of greater significance, a strong upper low is
expected to move into the western Bering early on Monday. With its
arrival increasing gales are forecast to expand across much of
the western Bering and Western Aleutians along with developing
storm force winds west of Saint Matthew Island through Tuesday
night. Resultant peak seas of 20+ feet are forecast from the
Western Aleutians, northward.

&&

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

Looking ahead at the longterm forecast, a strong ridge builds
over the southern Mainland while a cutoff low lingers south of the
Gulf of Alaska. Benign conditions under the stagnant ridge and
across the southern Mainland are expected to persist into the
weekend though this pattern may lead to widespread fog at lower
elevations. Above average daytime highs and overnight lows are
also anticipated through the long term. There is average
confidence that a front may clip the north Gulf coast on Saturday
morning.

Out west, an upper-level trough and attendant surface low inhabit
the western Bering and Aleutians on Wednesday. However, decent
model spread still exists with the low track and strength which
will affect associated impacts. The GFS and Canadian solutions are
currently the strongest as they advertise winds up to storm force
between Shemya and Adak and over parts of the Bering. The
Canadian low is much quicker in lifting to the north to Russia
already by Wednesday morning, while the GFS low does not reach
Russia until Thursday. The EC is overall the slowest and weakest
solution as it produces only small crafts by the time it tracks
near Adak late Wednesday morning, weakening as it moves into the
Bering thereafter. Fortunately, there is better model agreement on
another low set to reach the western Aleutians for Friday and
Saturday. At this time, there is consensus between the GFS and
Canadian for widespread rain and gale force winds to accompany the
low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 119 120 125 131 139 351 352 177 178 180 181
411 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CJ
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
LONG TERM...AF

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
224 PM AKST Sun Nov 13 2022

AKZ101-111-142100-
Anchorage-Matanuska Valley-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Palmer, Wasilla, Sutton, and Chickaloon
224 PM AKST Sun Nov 13 2022

...ICE JAMS IN THE ANCHORAGE BOWL AND MAT-SU VALLEY...

The abnormally cold temperatures the past few weeks caused ice
formation on area rivers and streams across the Anchorage and Mat-
Su valleys. This ice formation is causing ice jams, and has led
to localized overflow flooding in the vicinity of the jam. Warming
weather this weekend has continued to enhance ice movement on the
waterways, and continued low land overflows are expected through
the first part of this week.

Currently, widespread ice jams are being reported on streams in
Anchorage and across other waterways including Wasilla Creek.

With temperatures at or above freezing, water levels may rise
further due to runoff from snow melt. As the week progresses, ice
jam issues should begin to subside as the warmer temperatures
erode lingering ice cover, which will allow water levels to
decrease.