Small Craft Advisory 68, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 PM AKST Sun Jan 23 2022

.ANALYSIS AND UPPER LEVELS...

The upper level pattern features a longwave trough across the
Bering Sea extending into the western Gulf and Southcentral Alaska.
While a blocking ridge persists across the eastern Pacific extending
to the ALCAN border. Satellite shows a short-wave supporting a
weak front moving across the northern Gulf and inland this
afternoon. This short-wave is bringing some areas of light rain
near the coast and snow to the higher elevations. Inland valley
areas may see a brief period of rain or snow with no accumulations
expected. Farther south a deep low pressure system south of the
AKPen is moving north with a warm front pushing from the North
Pacific into the Gulf later today. Radar shows some light rain
over the northern Gulf pushing into Prince William Sound. Also a
band of rain and snow is moving north from the Cook Inlet brushing
the western Kenai Peninsula and into the southwest part of the
Susitna valley. Across Bristol Bay radar is showing snow and rain
moving in ahead of the deep low to the south. Temperatures are
mostly in the 30s and 40s with the warmest areas being along the
Turnagain arm and west Anchorage as the Turnagain winds continue
this morning. Gusty winds and warm temperatures also continue
across the Matanuska Valley, with the Knik River Valley winds
kicking in this morning. Most inland valleys are in the 30s
currently with light winds. Across Bristol Bay temperatures are
above freezing from King Salmon to Iliamna as downsloping and
gusty easterly flow has warmed the area. Across the Kuskokwim
Delta temperatures are in the teens with northerly winds up to 25
mph. Across the western Bering northerly flow dominates with snow
showers, while the eastern Bering and AKPen are warmer as warm,
moist flow from the low pressure system to the south brings
increasing winds and rain.

&&

.MODEL DISCUSSION...

Models are in good agreement through the short term and have come
into better agreement with the low pressure system moving north
towards southern Alaska. Precipitation types will still be a
challenge mainly for Southwest Alaska, but may also be a challenge
across Anchorage and the Matanuska Valley as timing the Turnagain
winds and Knik Winds will determine if the precipitation is rain
or snow. Either way precipitation should remain light through
Monday. Finally as mentioned above, timing the down inlet winds
and the Turnagain winds bending into Anchorage could be tricky
this evening through tomorrow afternoon as the next low pressure
system tracks north.

&&

.AVIATION...

PANC...VFR conditions are expected through the TAF period. Winds
will be tricky due to subtle changes in the north-south pressure
gradient sin Cook Inlet, which will affect whether the southeasterly
Turnagain winds bend into the terminal. With the deep low crossing
the Alaska Peninsula and moving into the far eastern bering Sea
this evening and its associated front crossing the western Gulf,
pressure gradients will favor the Turnagain winds bending just
south of the terminal. Exact timing is hard to determine, but
expect sometime between 06Z and 12Z. Surface winds will likely
shift to light northwest while strong southeasterlies persist
above the surface, so low level wind shear is likely. Southeast
winds will then move back in with frontal passage, which is
expected between 18Z and 22Z on Monday.

&&

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

Significantly warmer temperatures as a result of downsloping are
seen across Anchorage and the Matanuska Valley today, with highs
well into the 40s. As a low tracks northward across Bristol Bay,
its associated front in combination with a deep southerly fetch of
moisture aloft will lead to rain along the Gulf coast and the
development of high winds along Turnagain Arm. A High Wind Warning
is in effect from late this evening through Monday morning for
west Turnagain Arm and higher elevations of Anchorage. Winds will
gradually diminish through the day Monday as the aforementioned
low tracks northward, however precipitation will continue along
the coast. As temperatures cool aloft, lingering moisture from the
front may briefly fall as light snow late Monday into early
Tuesday across Anchorage and the Matanuska Valley. Skies will
clear from west to east Tuesday into Wednesday as a more offshore
synoptic flow pattern develops. This will significantly cool
temperatures and allow for the first appearance of prolonged
sunshine in several days.

&&

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

A band of mixed precipitation is now spreading north across
nearly the entire Southwest as a large low pressure system begins
to cross over the southern Alaska Peninsula into the far eastern
Bering. Strong winds gusting over 50 mph at times have already
picked up across Bristol Bay, with downslope warming and warm air
advection with these winds pushing temperatures above freezing and
changing ongoing precipitation over to rain. These winds will
continue overnight tonight, with gusts over 60 mph possible
through tomorrow morning, particularly near the western Alaska
Range and through the Kamishak Gap. Farther to the north, winds
have yet to reach into the Middle Kuskokwim Valley, where colder
temperatures and mainly snow is expected through tonight.
Temperatures will similarly rapidly warm above freezing with the
onset of the southeast winds early in the day on Monday, with a
transition briefly to sleet and freezing rain possible before a
changeover to all rain likely for the rest of the morning as
surface temperatures warm above freezing.

Out across the Kuskokwim Delta, precipitation will likely remain
all (or mostly) snow west of Bethel, where colder air wrapping
into the low from the north should be enough to keep low level
temperatures from warming above freezing. Gusty winds along the
Kuskokwim Delta Coast will cause periods of blowing snow, though
the heavy, wet nature of the falling snow should reduce the
potential for more significant blowing and drifting and any
extended periods of low visibility. Some mixing with or even a
changeover to rain is possible for a brief period near and east of
Bethel, with brief mixing with sleet and freezing rain again
possible during the morning where warm air just above freezing
manages to overrun the cold air sitting in place at ground level.
A Winter Weather Advisory has been issued for the Kuskokwim Delta,
mainly due to the potential for heavy snowfall amounts up to 10
inches along the Kuskokwim Delta Coast through Monday afternoon.

Late in the day on Monday, a strong cold front will work much
colder air in from the west as the parent low moves up towards the
Seward Peninsula. This will quickly change any remaining rain or
mixed precipitation over to all snow, with the snow ending from
west to east through Monday night. Quieter and drier conditions
will continue from there for most of the outlook area through
Wednesday, with bitter but not excessively cold temperatures
ranging from a few degrees below 0F to the low teens above.

&&

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

Two main storm systems will impact parts of the Bering region
through midweek, with the first system now in the process of
crossing over the Alaska Peninsula into the eastern Bering.
Northerly winds up to gale force will continue near the low as it
tracks north towards the Y-K Delta through Monday. The northerly
winds will advect much colder air around the low as it departs to
the north, changing areas of rain and snow mix over to all snow
before clearing out by Monday afternoon.

Farther west, ambient conditions will remain quiet up until
Wednesday as scattered snow showers follow weak waves of energy
working around a high pressure ridge drifting over the central
Bering. Early Wednesday, a deep low pressure system will send a
front into the western Aleutians, sending a corridor of easterly
winds to storm force across along with a band of rain and snow
becoming all rain by Wednesday evening. The strongest winds should
remain generally west of Adak, with gusts near Hurricane force
possible farther west near Shemya early on Wednesday morning.

&&

.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 Sea/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 phase 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...High Wind Warning 101.
         Winter Weather Advisory 155.
MARINE...Gale Warning 119 120 125 130 131 132 136 137 138 139 141
                      150 160 170 172 174 180.
         Heavy Freezing Spray Warning 160 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
MARINE/LONG TERM...MF