Small Craft Advisory 70, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKST Mon Jan 24 2022

.ANALYSIS AND UPPER LEVELS...

A large, slow moving and weakening low moves over Southwest Alaska
later this morning. Meanwhile, its front, also slow moving, pushes
onshore over the North Gulf Coast and into Anchorage. There is a
long moisture fetch associated with the front, forcing copious
amounts of precipitation across the Gulf and along the Coast. Anchorage
will remain downsloped out of any significant precipitation on
Monday but may see some light snow by early Tuesday morning.
Above freezing temperatures will persist across almost the
entirety of Southern Alaska, with the exception of the Kuskokwim
Delta Coast (specifically, areas west of Bethel), through at least
late Monday night, or until the low pushes north of Bethel. Cold,
arctic air will be reintroduced over Southwest Alaska by Tuesday
morning and then filter into Southcentral by Tuesday night. Areas
of snowfall are likely across the Susitna Valley and Anchorage
areas once the cold air moves in.

&&

.MODEL DISCUSSION...

Models are in good overall synoptic agreement through the short
term. There are some discrepancies regarding the possible
development of a triple point low west of the Barren Islands on
Monday night. The GFS/Canadian hint at one forming, while the
EC/NAM remain as an open wave. The NAM eventually develops a
surface low within PWS by Tuesday morning, which the Canadian is
further south and the GFS even further south still. Solutions
have a rather good handle on the large low approaching the western
Bering on Wednesday, with only some minor differences on center
location and system strength. Additionally, models are gradually
nudging a North Pacific low further northwards over the past few
runs as it approaches the Gulf of Alaska on Wednesday.

&&

.AVIATION...

PANC...VFR conditions will persist through today. Northerly winds
will continue through the morning hours and then transition to
gusty southeasterly winds for the afternoon and evening. Cloud
ceilings are expected to drop below 5000' by this evening and
continue to gradually lower through the night and winds will begin
diminishing. Additionally, expect some light snow and periods of
reduced visibilities late tonight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

The warm temperatures will continue today and into tonight over
Southcentral as the tap of warm air that can be traced back on
satellite to almost 25N remain over the area. The surface low is
in Bristol Bay and weakening as the main front will move
northward over the region this morning. The winds along the front
have been gusty but a bit less overnight than had been advertised
by the high resolution models. The old-school pressure nomograms
did a better job with getting the winds correct for Turnagain Arm
and the Anchorage Hillside winds.

Moving into the upcoming forecast for this afternoon
through tonight, there is a tricky situation setting up in the
northern Cook Inlet area and into the Susitna Valley. Cold air
will begin to filter in through the Kamishak Gap this evening and
overnight, but the main pool of cold air will remain dammed up
behind that Alaska Range until tomorrow. Models do want to cool
down the temperatures enough to turn precipitation from rain to
snow from southwest to northeast up Cook Inlet as the night
progresses. The only problem is that the change in precipitation
type may not happen nearly as quickly as models are indicating.
The problem is that it has been warm and into the 40s the past few
days with many locations not even getting back below freezing at
night. The southerly winds will persist tonight and especially in
the Anchorage area. When these antecedent conditions occur, the
precipitation often ends before the airmass can cool enough to
turn to snow. Therefore kept the rain in the forecast overnight
and then turned it to snow late tonight as southerly winds start
to die down. Could it still turn to snow earlier and cause a few
inch accumulation? Yes, and that is the forecast challenge and
potential bust. However, it looks most likely to remain mostly
rain from the Kenai Peninsula northward through the Matanuska
Valley. The Susitna Valley will be more of a transition area with
rain in the south and snow farther north.

The colder air moves in Tuesday and temperature will cool
noticeably from where they have been to more seasonal values
through the remainder of the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

The longwave pattern features a broad trough over the central Bering
and Western Alaska. There is a surface low near Kuskokwim Bay
this morning and it has a post frontal trough that is over the
Alaska Peninsula this morning. The surface low will move inland
later this morning bringing additional snow, a wintry mix or rain
to Southwest Alaska today. The low will lose its gusto as it moves
inland but expect moisture to work its way towards the western
Alaska Range. In the wake of the frontal passage, a transient high
will move into Southwest Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

The longwave pattern features a broad trough over the central Bering
and the North Pacific and it has worked its way into the Gulf Of
Alaska. The models are all trending towards an active pattern
with back to back North Pacific lows impacting the Aleutians. The
first surface low is near Kuskokwim Bay this morning and it has a
post frontal trough that is over the Alaska Peninsula this
morning. The surface low will move inland later this morning but
there is still moisture and a tight pressure gradient that will
impact the Eastern Aleutians into the evening. There is a weak
ridge behind this system. By Tuesday morning a 950 mb low will be
south of Shemya. The models track this low towards the Western
Aleutians Tuesday evening. And at least one of the models is
showing this system to further intensify to 948 mb Tuesday night.
Impacts-wise expect storm force winds (hurricane force gusts) and
enhanced seas along with a robust precipitation shield. Stay tuned
for more updates.

&&

.MARINE (Days 3 through 5 - Wednesday through Friday)...

Gulf of Alaska: A front extending from a North Pacific low will
advance toward the northern gulf coast beginning on Wednesday.
Expect localized areas of gale force winds to develop from Cook
Inlet through Shelikof Strait and continuing through Friday.
Forecast confidence is moderate.

Bering / Aleutians: A strong North Pacific low with an associated
gale force front will approach the southern Bering early
Wednesday morning. Widespread gale force winds with a potential of
storm force gusts and elevated seas above 20 ft will extend from
the western Aleutians to the northern Bering through Thursday
afternoon. Model guidance are in good agreement with keeping most
of the active weather west of the Pribilof Islands and central
Aleutians as the low pushes northwestward. A second North Pacific
low will approach the southern Bering on Friday morning. There is
a potential for another round of gales and elevated seas extending
across the same regions for the rest of day Friday. However,
there is model uncertainty with the overall track, position, and
strength associated with this low. Therefore, forecast confidence
is low to moderate.

&&

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

Looking ahead into the extended forecast, the latest operational
model runs are in decent agreement with the synoptic scale
features in the short term, but begin to diverge toward the end of
the period. Synoptically, an omega blocking ridge will setup in
the eastern Bering Sea. Downstream of the ridge, an Arctic trough
over the Alaska mainland will move southward beginning on Friday
and eventually phases with an upper level low in the Gulf.
Although there is uncertainty in the details as far as the timing,
the consolidated low will push east and south towards the
Panhandle. As the low exits out of the area, precipitation will
taper off for Southcentral, especially along the northern Gulf
coast from Saturday to Sunday. Benign conditions with temperatures
near to or below normal will prevail for the southern mainland as
the aforementioned ridge shifts over the state. Out west, a
series of North Pacific lows will move north across the Western
Aleutians, bringing periods of wind, rain/snow mix, and elevated
seas at times for the northern Bering Sea. Some of the
precipitation and wind may extend across the Pribilof Islands and
the Central/Eastern Aleutians as we head late into the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155
MARINE...Gale Warning 119 125 130 178 180 414
		 Heavy Freezing Spray Warning 160 185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...MF