Small Craft Advisory 306, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
538 AM AKDT Thu Apr 7 2022

.ANALYSIS AND UPPER LEVELS...
A cold upper level low continues its slow southward movement
through the Bering Strait. Ahead of the low several smaller
disturbances are tracking southeastward toward the Alaska
Peninsula as well as a southward moving front currently over the
Pribilofs. Very little snow if any has been observed with the
front's passage at Saint Paul and the front is expected to
gradually weaken upon reaching the Aleutians. A surface trough
extends over the Alaska Peninsula and into the Pacific side just
south of Kodiak Island. Light snow showers are lifting northward
from the trough and across King Salmon this morning. Much of the
Susitna Valley from Sparrevohn to Sleetmute is also experiencing
light snow, though accumulations should remain minimal. Further
east, a 992 mb low over the eastern Gulf is gradually lifting
northward toward the Gulf Coast. While precipitation chances may
increase somewhat on Friday, much of Southcentral is experiencing
dry conditions as general high pressure currently sits over the
region.

&&

.MODEL DISCUSSION...
While models are in good synoptic agreement this morning, subtle
differences exist with how models handle the progression of a
current upper level low situated over the eastern Gulf through the
next 24 hours. Placement of the low is different between each
model by Thursday night. Models agree that the low will steadily
weaken as it approaches the coast, with a trough south of Kodiak
Island eventually absorbing what remains of the low to the east
Friday morning. Despite initial differences in surface low
placement late Thursday, effects on the overall forecast should
remain minimal. High pressure builds into the southern Bering on
Friday while scattered snow chances develop across parts of
Southcentral Friday into Saturday.

&&

.AVIATION...
PANC...VFR conditions and calmer winds will prevail over
Anchorage on Thursday. Weak high pressure is expected to precede
the approach of the next upper level low. The low will see snow
chances return to the forecast Friday morning. Forecast confidence
in snow across PANC is below average; however, IFR conditions may
develop if snow manages to move off the Hillside.

&&

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

Weak ridging over the area has helped to allow for some clearing
across Southcentral, with the aurora appearing on some of the
webcams in the area. This ridging should help to keep much of
inland Southcentral dry today, with a mix of sun and clouds. A
vertically stacked low over the eastern Gulf is moving northwest
and will continue to do so through tonight. This will result in a
return of some precipitation along the Gulf Coast primarily
tonight. The low will then track into western Prince William
Sound, which should allow for some precipitation to sneak over the
mountains into Anchorage and the Mat Valley Friday morning. As the
forcing with this low is quite weak, there is quite a bit of
disagreement in the guidance. There is a chance that the
precipitation will result in a significant accumulation, while
there is a similar chance that no significant precipitation
occurs. Stay tuned.

Precipitation or not, on Friday the cold air that has been lurking
over Southwest Alaska for much of the past week will begin to
squeeze through the Alaska Range gaps into Southcentral. Expect
increasing northwesterly winds through the day on Friday, with
temperatures struggling to climb through the 30s. The winds will
be strongest through the Barren Islands, where Storm Warnings are
in effect. However, the gap winds through Passage Canal and
Resurrection Bay will gust to 35-45 mph as well Friday and
especially Friday night. The winds may help to keep temperatures
up a bit on Friday night, but of course anywhere the winds calm
down should result in temperatures falling to around 10 degrees.
Except through the aforementioned gaps, the winds should die down
for most of the area by Saturday night, which for many areas may
be cooler, despite quickly warming temperatures aloft by then.

The outflow northwesterly winds Friday night through Saturday
should very effectively clear out all of the moisture in the
atmosphere, so Saturday looks to be a gorgeous, sunny day all
across Southcentral.

&&

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

The longwave pattern features a broad trough over the Bering with
an Arctic low near the Bering Strait. The Arctic low will
continue to move southward over the eastern Bering Sea. An upper
level wave that is currently south of Sand Point will phase with
the Arctic low. As this happens, weak shortwaves will support
intermittent snow showers for the coastal and inland areas. The
snow showers will be favored for the upslope areas along the
Aleutian/Alaska Ranges and Kuskokwim Mountains. Late Friday, the
trough axis shifts eastward and a dome of high pressure builds
over the central and eastern Bering.

&&

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

The longwave pattern features a broad trough over the Bering with
an Arctic low near the Bering Strait. The Arctic low will
continue to move southward over the eastern Bering Sea. Snow
showers are possible near the Pribilof Islands and St Mathew. An
upper level wave that is currently south of Sand Point will phase
with the Arctic low. Its a progressive pattern and high pressure
will move across the Bering Friday and Saturday. The ice has made
it south of St Paul Island and is less than 5 nm from St George.

&&.Marine (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska: An Eastern Gulf low dissipates for Sunday. High
pressure moves across the Western Gulf through Monday. Forecast
confidence is good, except for variations in wind developments
around Kodiak Island. Gusty Northwest winds with areas of gales
through Kamishak Bay, Barren Islands and around Sitkinak extends
into the Western Gulf, diminishing Sunday. Seas to 12 feet across
the Western Gulf, subsiding.

Bering Sea: A front over the Northern Bering moves into the
Chukchi Sea for Sunday. A ridge across the Bering moves into the
Mainland late Sunday. A well developed North Pacific low and front
approaches the Western Aleutians for Monday. Forecast confidence
is good. Widespread gusty Southwest winds with areas of gales
diminish across the Northern Bering Sunday. Seas to 15 feet,
subsiding. Gusty Easterly winds with areas of high end gales along
the Aleutians become Southeasterly as they spread into the Bering
through Monday. Seas build to 20 feet on the Pacific side of the
Aleutians on Sunday, and to 15 feet over the Western and Central
Bering through Monday.Freezing spray is expected in ice free
waters over the Alaska Peninsula, Aleutians and Southern Bering,
and also around Nunivak Island through Sunday.

&&

.Long Term Discussion (Days 4 through 7: Sunday through Wednesday)...

A strong blocking ridge will build over mainland Alaska Sunday
through Monday. The big question is how long it will remain in
place. Ensembles and most of the operational models indicate the
ridge holding through most of the work week. The GFS is the
outlier with its depiction of a progressive wave pattern, with
the ridge moving to Southeast Alaska by Wednesday. Based on the
presence of a strong ridge, expect dry conditions over southern
Alaska, with warming temperatures as we head through the week.
Skies will be mostly clear, so expect a large diurnal range in
temperatures from early morning lows to late afternoon highs,
on the order of 20 to 25 degrees. As a result, expect a daily
freeze/thaw, as is typical for this time of year.

Meanwhile, a long-wave trough will settle over the Bering Sea
and Aleutians, with a steady supply of storms tracking across
the region. Thus, expect wet and windy conditions through the
week. Depending on the position and strength of the ridge over
mainland Alaska, some of these systems could reach the Southwest
Alaska coast, especially late in the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm 130.
         Gale 131 132 138.
         Heavy Freezing Spray 130 160 180 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...KZ/SEB