Small Craft Advisory 477, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
738 AM AKDT Wed Jun 22 2022

.ANALYSIS AND UPPER LEVELS...

At upper levels, a large low and weakening surface component is
located over the Alaska Panhandle. Following in the wake of this
low is a broad ridge of high pressure that extends from the
central Aleutians northeast to the central part of the Alaska
mainland. Shortwaves continue to ride over the top of the ridge to
the the southeast. Another low is located over the North Pacific
near the western Aleutians with its associated surface front
pushing northeast across the Aleutians and into the Bering.

Across Southcentral, mostly clear skies prevail with the
exception of some convective clouds located along the Alaska Range
and Talkeetna Mountains. A few lightning strikes were observed
over the Talkeetna Mountains and central Alaska Range during the
overnight hours. For Southwest, subsidence ahead of the ridge is
keeping the inland Bristol Bay area and western Gulf clear and
dry. Westerly flow near the surface is advecting a stable marine
airmass associated with the ridge over Bristol Bay waters, the
Kuskokwim Delta, and the Alaska Peninsula. Farther west, the front
extending from the North Pacific low is spreading rain and south-
southeasterly winds up to small craft across the western
Aleutians. A low stratus deck continues to blanket much of the
Bering while the front gradually approaches from the west. There
is also a band of upper level clouds spread across the Bering that
has entered the Kuskokwim Delta this morning.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement through the short term
as they all illustrate an upper-level Bering ridge continuing to
build eastward over Southwest and then across Southcentral. There
remains some discrepancy with respect to the timing and strength
of various shortwaves dropping south across Southwest and
Southcentral, downstream of the ridge. Models depict a shortwave
tracking southeast across Southwest Alaska today, and the 00z GFS
is currently the quickest to bring the shortwave through the
region.

&&

.AVIATION...
PANC...VFR conditions will persist through the TAF period. A
westerly sea breeze is expected to develop by midday and will
continue through the evening hours. Light and variable winds will
return for the overnight hours.

&&

.FIRE WEATHER...

Warm and dry weather is expected across Southcentral through the
early weekend. Isolated wet thunderstorms are possible over the
Talkeetna Mountains and Copper River Basin this afternoon, however
thinking that development will be limited with building ridge
overhead. Hot, dry, windy conditions don't look to line up in
conjunction anywhere in Southcentral, but certainly very warm
conditions will be widespread. Isolated wet thunderstorms are
looking increasingly likely Thursday afternoon as an upper level
wave approaches from the west, generating enough lift for showers
and thunderstorms to develop. The best chances for storm
development will be over the Copper River Basin. Convective
parameters are looking minimal on Friday, though an isolated
shower or wet thunderstorm is possible over the eastern Copper
River Basin.

Temperatures across Southwest will be offset somewhat by the
approach of a shortwave trough from the northern Bering Sea on
Wednesday, with most locations failing to climb above 70 degrees.
Low stratus as well as high clouds continue to expand eastward
across the Kuskokwim Delta and will likely continue to overspread
portions of the Lower Kuskokwim Valley and Bristol Bay. While
precipitation chances will be very low indeed, the passage of the
disturbance and a lee side trough over Bristol Bay will promote
increasing winds late into the day and especially later tonight.
Winds of 15+ mph may gust up to 25 mph through early Thursday
morning, while also help to delay rebounding RH values. Finally, a
small threat of isolated thunderstorms will develop over the
Alaska Range, primarily to the east and northeast of Sparrevohn
later this evening. Beyond that, thunderstorm chances should drop
to nearly zero through the next several days. Though daytime
temperatures will certainly continue to warm through the end of
the week with afternoon highs in the upper 70's.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Today through Thursday
evening)...

An upper level ridge will build in over Southcentral from the
west today. Gusty outflow winds along the northern Gulf coast this
morning will eventually diminish as the ridge moves eastward.
Southcentral will see warm and dry conditions with locations in
the Susitna Valley approaching temperatures in the low to mid 80s.
Isolated afternoon thunderstorms are possible over the Talkeetna
Mountains and Copper River Basin, though expect development to be
largely inhibited by the ridge. On Thursday, an upper level wave
traverses Southcentral from west to east, bringing an increased
chance for showers and thunderstorms Thursday afternoon,
particularly over the Copper River Basin. Conditions will remain
warm and dry again on Friday, with isolated showers developing
over the eastern Copper River Basin Friday afternoon. The ridge of
high pressure looks to persist into the weekend.

&&

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

A ridge of high pressure, which tilts northeastward across
Southwest, is being impinged upon by an upper level disturbance
moving into the YK Delta this morning. Conditions overnight across
the Lower Kuskokwim Valley and interior Bristol Bay have been
largely clear for all but the Alaska Peninsula. Low stratus and
higher clouds associated with the trough will expand eastward into
Southwest, having already covered the Kuskokwim Delta. In effect,
cooler daytime high temperatures are forecast for the region with
only the lower elevations and valleys of the Alaska Range to
climb above 70 degrees. The passage of the trough as well as a
surface trough over Iliamna Lake will promote northerly winds
gusting to 15 to 20 mph later tonight into the early morning hours
on Thursday from as far north as Lime village to as far south as
Iliamna and New Stuyahok. In doing so, lower RH values with
percentages in the lower 40's may linger longer into the overnight
hours.

The shortwave trough from Wednesday will depart the region to the
east by Thursday with high pressure to rebound and amplify over
Southwest through Friday. This will promote warmer temperatures
over Southwest but also calmer winds with little in the way of
precipitation. Of note, a longwave trough moving through the
Bering Sea will begin to shunt high pressure over Southwest to the
east, with a front to reach the Kuskokwim Delta coast Saturday
morning. Drier conditions and warmer temperatures will gradually
be replaced by increasing moisture and cloud cover with the
trough's arrival.

&&

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

The forecast over the Bering Sea and Aleutians is more
straightforward over the next few days. An upper low just west of
the Aleutians will bring a front eastward and into the southern
Bering Sea by Friday morning. Unsettled weather with scattered
showers and small craft to gale force southeasterly winds will
shift across the Aleutians from west to east, reaching the Eastern
Aleutians by Friday as the front finally begins to weaken. A
second trough of low pressure will lift ahead of the low late on
Thursday helping it to deepen into a broad longwave trough over
the Bering Sea. Scattered light showers will be common across the
Bering Sea along with continued cloudiness and unsettled
conditions.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Bering/Aleutians: Eastern Bering high pressure moves inland
through Saturday. A Western Bering low moves through the Gulf of
Anadyr, while its front extends through the Central Bering and
Eastern Aleutians to a another low in the North Pacific South of
Dutch Harbor for Saturday. Forecast confidence is fair due to the
movement of the front. Widespread small craft winds with areas of
gales with the front move into Eastern Bering, diminishing Sunday.
Seas to 14 feet, subsiding.

Gulf of Alaska: High pressure lingers across the Gulf through
Sunday. Forecast confidence is good. Generally light winds over
the Gulf. Seas mostly 6 feet or less.

&&

.Long Term Discussion (Days 4 through 7: Saturday through Tuesday)...

A ridge will continue to build over the state this week in a Rex
block pattern with a stalled, large low located south of the Gulf
over the Pacific Ocean. An embedded shortwave will develop along
the ridge axis later in the week as it moves east. By Saturday
morning, the trough will be located over eastern Alaska near the
AlCan border. As the trough becomes influenced by the blocked flow
pattern, it may slow and drop south throughout the day Saturday.
The ridge however will remain in place over Alaska so while the
overall weather pattern is expected to lean warmer and drier than
normal through the entire extended forecast, this shortwave may
allow for slightly cooler weather going into this weekend with a
brief period of unsettled weather possible, particularly for the
Copper River Basin and possibly into the Anchorage Southcentral
area. There is some uncertainty with regards to how far south the
shortwave will influence Southcentral, the timing, strength of
this trough, and its extent westward along its way south. The
latest model runs have it edging further towards the Anchorage
area than in previous runs. The strength of this ridge will
quickly push the low south. For many, the unseasonably warm
temperatures will continue. Any easterly waves over Southcentral
may introduce opportunities for thunderstorm activity.

Over the Aleutians and the Bering sea, a large low will move
through from the west towards the end of the week bringing gusty
winds and rain to the eastern Aleutians through Saturday.
Circulation could develop around the eastern Aleutians and AKPen
area Sunday afternoon that could lead to some unsettled weather
for the eastern Aleutians, AKPen, and toward Bristol Bay through
Tuesday. Model guidance beyond Sunday breaks down substantially
and there is low certainty in the progression of this circulation
as it will be influenced by the strength of the ridge over Alaska
and the shortwave over the east.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 175, 176, 177.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
MARINE/LONG TERM...KZ/VR