Gale Warning 674, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
557 PM AKST Wed Nov 16 2022

.ANALYSIS AND UPPER LEVELS...

A broad upper level ridge extends over the Alaska-Yukon border
along an axis from the Alaska Panhandle northward to the north
slope. Farther south over the Gulf, an upper level low is
positioned near 50N. Several upper level waves propagating around
this low are lifting over Kodiak Island and the Alaska Peninsula.
This feature has generated increased easterly winds, particularly
over the Alaska Peninsula and Bristol Bay coast where occasional
gusts have been occurring during the morning hours. Additionally,
a few light returns on radar suggest scattered showers spreading
across the Alaska Peninsula. Farther west, an upper level trough
in place over the Bering is gradually advancing eastward and
interacting with the feature over the Alaska Peninsula. A sharp
boundary between these two features can be observed on satellite
imagery with a swath of high level cloud cover extending north to
south over the central Bering. Elsewhere over Southcentral, skies
remain generally clear under the ridge of high pressure with the
exception of the Copper River Basin where fog and low level
stratus persist.

&&

.MODEL DISCUSSION...

Overall, synoptic model agreement is good. There are some minor
differences regarding the interaction of the western Bering trough
and the upper level waves associated with the Gulf low, however
the resultant weather will not vary much. By Thursday afternoon,
models are showing differences in an upper level wave over the
eastern Bering that will ultimately affect the timing and duration
of precipitation along the Alaska Peninsula and Southwest coast,
including the Kuskokwim Delta. Currently the 12Z GFS run appears
to be an outlier, suggesting multiple breaks in precipitation,
while the NAM/EC/Canadian solution all suggest less a intermittent
event. By the end of the week, all models have keyed in to a Gulf
low approaching the southern mainland Friday evening into
Saturday. At this time, there are still differences in position
and strength of this low, however there is increasing confidence
in active weather across Southcentral this weekend.

&&

.AVIATION...
PANC...VFR conditions and light northerly winds will persist
through the TAF package.

&&

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

A large and strong upper-level anticyclone centered near the ALCAN
border this evening will slowly shift eastward through the end of
the week. This will promote dry, mostly clear conditions as its
large area of influence continues to span across Southcentral
Alaska. Warm air moving over top of cooler air sitting at/near
the surface will continue to maintain or strengthen existing
temperature inversions. This is typically a great set-up for fog.
However, pressure gradients between surface high pressure over
mainland Alaska and a deep low in the North Pacific will produce
just enough wind to limit fog formation for most locations. Fog
and stratus potential may increase somewhat each night as low-
level flow weakens gradually over the coming days with the
eastward retreat of strong high pressure, though overall it will
remain not favored. The main exception is the Copper River Basin,
where fog and stratus look to remain entrenched until the pattern
changes and breaks down or weakens the inversion. The arrival of
a Gulf low on Friday may herald such a change.

Until then, active weather remains far to the south over the
southwestern Gulf of Alaska as a series of shortwaves rounds the
low in the North Pacific, bringing periods of rain to Kodiak
Island through the remainder of the week. The first main shortwave
exits northwest tonight, which should end the heaviest
precipitation for the island. Thursday morning onward, persistent
easterly upslope flow will maintain low clouds and visibility
along the east side of Kodiak Island and the potential for light
rain showers.

By Friday, the ridge shifts far enough east to allow the trough
over the Pacific to lift northward into the Gulf. There has been
some refinement with the timing and track of this trough and its
associated shortwaves and surface features, but some uncertainty
remains. The main takeaway is that precipitation is likely to
begin along the Gulf coast on Friday evening, with a more well-
defined front arriving by Saturday. Along the front, winds may
increase to gale force with the development of a barrier jet,
while heavy precipitation is expected for the coastal mountains.
Precipitation overrunning the mountains looks to be limited at
this time, with low-level northeasterly flow keeping inland
locations mostly dry through the weekend.

&&

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

The main story for Southwest Alaska will be the potential for
freezing rain or freezing drizzle from tonight through Thursday
afternoon. A Special Weather Statement has been issued to
highlight this hazard, with little to no ice accumulations
expected. Freezing rain/drizzle potential tonight will hinge on
how quickly temperatures increase above freezing. Surface
temperatures today increased very quickly, suggesting that warm
air advection may be strong enough to preclude freezing rain
altogether. However, with low temperatures hovering around
freezing for parts of the Kuskokwim Delta and along the
Kuskokwim Mountains, freezing rain is not out of the question.

The other puzzle piece in the freezing rain puzzle will be where
precipitation occurs. Shortwaves transiting along a ridge over
Mainland Alaska are expected to bring light precipitation along
the Southwest Alaska coast. The placement and strength of these
upper level shortwaves depends on how strong the ridge is, and
model representation of shortwave-driven precipitation tends to be
poorer as compared to well-defined surface features. This forecast
package differs from the previous by shifting the band of
precipitation further east, increasing precipitation chances and
amounts where the vertical temperature profile favors freezing
rain. Overall confidence in where freezing rain/drizzle will occur
is on the lower side, but the totality of factors (strong warm
air advection, lighter precipitation) point towards little to no
ice accumulations.

Quieter weather should be in store for Friday and Saturday. Though
precipitation chances will linger over the Kuskokwim Delta through
Friday, most of Southwest Alaska should see clearing skies and
cooling temperatures.

&&

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

A shortwave over the Pribilof Islands is merging with a
stationary front over the Central Bering Sea. The interaction of
these features is currently bringing a resurgence of rain over the
Central Bering and Pribilof Islands. However, winds and
precipitation should begin to diminish by Thursday morning as the
merged low moves north into the Bering Strait. The next feature to
watch will be a North Pacific low that moves towards the Western
Aleutians on Thursday night. Expect small craft to gale force
winds along the Western and Central Bering and Aleutians, with
rain transitioning to a rain/snow mix along its front.

&&

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

Looking ahead in the extended forecast, the latest model runs and
ensemble guidance are in fairly decent agreement with the
evolution and progression of the synoptic features. The
anomalously strong upper ridge over Alaska breaks down on Sunday.
In the short term, the main storm track will stay to the south
with low pressure systems tracking northward into the Gulf of
Alaska. Although there are positional and track differences with
these features, a couple of upper level shortwaves and surface
lows brings precipitation and gusty winds along the coastal areas
of Southcentral. As the aforementioned ridge shifts east early
next week, moisture and precipitation increases further inland and
into Southwest Alaska.

Out west, a deep trough and strong upper low over eastern Russia
moves southward into the Bering Sea between Monday and Tuesday.
For the eastern Aleutians and Alaska Peninsula, the main feature
to note is the colder air advection promoting localized gusty
winds out of the bays and passes. Cold, northerly flow over the
relatively warm waters will also help generate widespread showers
over the Pribilof Islands and along the Aleutian Chain. By
midweek, a ridge will build across the western Aleutians with a
brief break of drier conditions.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales: 131, 138, 150, 180, 181
FIRE WEATHER...NONE.

&&

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

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
142 AM AKST Thu Nov 17 2022

AKZ152-155-161-171145-
Lower Kuskokwim Valley-Kuskokwim Delta-Bristol Bay-
Including the cities of Aniak, Sleetmute, Bethel, Nunivak Island,
King Salmon, Dillingham, Naknek, and Pilot Point
142 AM AKST Thu Nov 17 2022

...FREEZING PRECIPITATION NO LONGER EXPECTED TONIGHT THROUGH
THURSDAY AFTERNOON...

Temperatures across the Kuskokwim Delta and inland areas along
the Kuskokwim Mountains are too warm to expect freezing
rain/drizzle from the remainder of tonight into tomorrow
afternoon.