Small Craft Advisory 121, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 AM AKST Fri Feb 10 2023

.ANALYSIS AND UPPER LEVELS...

A broad upper level trough extends across eastern Russia, the
Bering Sea, and much of Alaska. Several upper level lows are
embedded in this trough, with the most prominent one being a
vertically stacked low currently over the Eastern Aleutians. This
low has been and will continue to be the primary influence on
weather across the forecast area. Strong winds across the Aleutian
Chain and Alaska Peninsula have diminished overnight as the low
and its front progress eastward. Meanwhile, Saint George Island
continues to experience blizzard conditions as gusts up to 70 mph
blow about light falling snow. Southwest Alaska and Kodiak Island
are seeing increasing cloud cover and snow intensity as the front
enters the mainland and Gulf of Alaska, with some locations in
Southwest Alaska recording visibilities as low as 1/4 mile. As
for Southcentral Alaska, the main story continues to be lingering
low stratus at low elevations and flurries/light snow from this
cloud deck, with increasing high clouds portending the arrival of
the front later today.

&&

.MODEL DISCUSSION...

Models are in great synoptic agreement through the short-term for
the stronger lows moving across the forecast area. Models are
having a more difficult time capturing a weaker system moving from
the North Pacific into the Gulf of Alaska on Saturday and Sunday.
The current forecast package leans on the more aggressive
GFS and ECMWF models in contrast to the weaker solutions with the
NAM and Canadian models. Interestingly, the GFS and NAM have been
holding steady in their respective camps for the 00Z and 06Z
runs. Overall, the impacts will mainly concern gap winds through
the Gulf of Alaska and the Alaska Peninsula, as well as
precipitation for Kodiak Island and Prince William Sound.

&&

.AVIATION...
PANC...VFR should persist, with snow not expected again until
tomorrow afternoon. There is the potential for low-level wind
shear in the afternoon as easterly winds aloft develop with the
approaching front. However, current thinking is that strong down-Inlet
flow will keep winds northerly up to 2000 ft.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Friday
through Sunday night)...

Clouds and a few scattered flurries persist across interior
Southcentral this morning due to lingering low-level moisture and
weak flow in the lower and mid-levels of the atmosphere. However,
as these winds shift to the south ahead of an approaching front,
the lingering low clouds are expected to diminish in coverage.

A storm-force front will move from the western Gulf to the
northern Gulf today. Expect widespread easterly gales across the
Gulf with storm-force winds near the Barren Islands this morning
and between Kayak and Montague Islands late this afternoon.
Widespread precipitation will accompany the front, with snow
across Kodiak Island early this morning changing to rain by mid-
morning as easterly winds usher in warmer air from open waters.
Several inches of snow area expected for Kodiak City before the
changeover to rain. The widespread snow will move over the Kenai
Peninsula later this morning and across the rest of the
Southcentral coast by early afternoon. Expect snow and blowing
snow for portions of the eastern Kenai Peninsula, namely Portage
Valley and Turnagain Pass, late this morning through Friday
evening as easterly gap winds increase to between 30 and 40 mph.
Snow and blowing snow will also develop for Cordova later today,
with the potential for blowing snow diminishing this evening as
temperatures warm.

By Saturday, the front will slowly lift onshore with snow
continuing across the higher terrain and a rain/snow mix for
coastal locations. Valdez and Thompson Pass will likely see the
bulk of the snow for Saturday as the front moves north and the
prevailing flow aloft shifts from the east-southeast to a more
southerly direction. Periods of blowing snow are also possible
for Thompson Pass this afternoon and again Saturday as wind
increase first ahead of the front then as the front lifts north
Saturday.

Models then diverge in their respective solutions beginning late
Saturday. While guidance does keep precipitation going along the
coast, there is some disagreement with the orientation of the
attendant upper-level trough as it moves over Southcentral. Given
the amount of moisture and upper-level support, however, it is
likely that locations along Cook Inlet north to the Mat-Su Valleys
see some light snow by late Saturday afternoon or evening, in
addition to some scattered flurries Friday afternoon and evening
coinciding with the initial push of moisture from the frontal
system. There is also model disagreement with the position and
strength of a secondary area of low pressure entering the Gulf
for Sunday. Whatever the track, the big takeaways with this
system will be the intrusion of a much colder air airmass over the
region from the west with colder temperatures and strong winds
for coastal locations along with areas of snow continuing into
next week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Friday
through Sunday night)...

The front extending off a storm force low in the Bering Sea moves
across Southwest Alaska today. Busy weather continues across the
region, with blowing snow conditions beginning across Bristol Bay
from Dillingham north and west, and blizzard conditions being
observed along the Kuskokwim Delta coast. A Blizzard Warning has
been issued for the Kuskokwim Delta and the Winter Weather
Advisory for Blowing Snow in Bristol Bay remains in effect. Snow
and gusty northeasterly winds will persist into this afternoon;
anticipate visibility issues to begin and/or continue until then.
Cold wind chills will also be a factor today, with 30 to 40 below
possible across Bristol Bay and the Kuskokwim Delta. Conditions
should begin to improve as the low pushes onshore later this
evening. Winds are expected to weaken and snow will begin to taper
off.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Friday through Sunday night)...

Storm force low lingers in the Bering Sea today, weakening and
pushing onshore later tonight. An area of storm force winds sits
within widespread gale force winds in the Bering Sea south of the
Pribilof Islands through this morning. Storm force winds will
diminish by late morning, but gales will hold on into this
evening. By tonight, winds will drop to small craft and continue
weakening through tomorrow. Cold air advection follows in its
wake, forcing the large area of heavy freezing spray to extend
southward along the eastern Bering Sea pushing into Bristol Bay
and nudging along the southern Alaska Peninsula. Areas of extreme
freezing spray are expected along the ice edge over the next few
days as well. Additionally, winds will ramp up through the gaps
and passed south of the Alaska Peninsula with the onset of cold
air advection.

Blizzard conditions have been observed overnight in Saint George
and are expected to continue into the early afternoon. Saint Paul
has managed to stay above Blizzard Warning criteria, but the gusty
winds and light snowfall that has been observed in Saint Paul
will continue through the morning hours.

&&

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

Active weather continues next week with a series of strong lows
forecast to track across the region. Forecast confidence continues
to be above average as models have been relatively consistent
with the depiction of several strong features. Models are in
better agreement with the handling of a cut-off low which will aid
in bringing colder temperatures to Southwest Alaska. While GFS
has shifted to depict a more consolidated feature, the consensus
has moved it north over the Bering Strait, which suggests that
temperatures may not get quite as cold. However, 850 mb
temperatures as low as -24C are still expected to work in over
Southwest Alaska for Monday. Remnant low pressure in the Gulf of
Alaska will continue to help draw this dense, cold air through
gaps along the coast of the western Gulf of Alaska. These winds
are likely to gust to storm force, with localized areas of
sustained storm force winds. A weak front tracking east from
Southwest Alaska combined with a strong shortwave passing aloft
will likely contribute to light snow for Southcentral Monday
morning. Accumulations inland look to be only a few inches at
most, and are likely to be greatest over the western half of
Southcentral. Gap winds diminish Monday night as the low in the
Gulf weakens. Shower activity decreases along the north Gulf coast
as well, with snow over inland Southcentral tapering off as cold,
dry air filters in on Monday.

At the same time, a strong storm or hurricane force low in the
North Pacific passes south of the Aleutian Islands. The low looks
most likely to track south of the island chain, dipping back south
over the North Pacific as it occludes on Tuesday. However, some
model solutions have suggested potential for the low to track
toward Bristol Bay, but this is not currently a favored solution.
The low pushes its front across the central and eastern Aleutians
early on Monday, bringing easterly winds as strong as storm force.
This also has the potential to bring snowfall to some of the
islands, though recent model solutions are a tad warmer with the
low compared to yesterday. Precipitation moves up along the Alaska
Peninsula into Bristol Bay and over Kodiak Island Monday evening
into Monday night. A weak triple point low then develops in the
Gulf of Alaska as the front pushes to the north Gulf coast by
Tuesday, bringing another round of precipitation there. A potent
shortwave tracking north into the Interior with the front may be
sufficient for much of southern mainland Alaska to see some snow
on Tuesday. Little warm air is expected with this system, but
there is some potential for rain at low elevations along the
immediate coast. Inland locations can expect to see all snow.
Precipitation gradually tapers off for Wednesday as the surface
low weakens and the broader upper-level trough lifts north.

Out west, a deep low near Kamchatka pushes a storm force front
into the western Aleutians late on Tuesday. Along with it comes a
southerly push of warmer air, which is likely to switch
precipitation over to rain as the front sweeps from the western
Aleutians to the eastern Aleutians through Wednesday. Uncertainty
grows by Thursday regarding how quickly the front progresses
eastward and whether it moves in over Southwest Alaska. A triple
point low looks more likely to drive north across the eastern
Aleutians/AKPEN into Southwest Alaska late on Thursday, bringing
warmer temperatures and a slight chance of mixed precipitation by
Friday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155 195.
         Winter Weather Advisory 125 161 171.
MARINE...Heavy Freezing Spray Warning 130 139-140 160 179-180 185
                      411-412 414.
         Storm Warning 119 130 139 155 413-414.
         Gale Warning 120 125 130 131-132 136-138 150 160 170
                      172-176 178-181 351-352 412.
FIRE WEATHER...NONE.

&&

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

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