Small Craft Advisory 488, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
533 AM AKDT Sun Jun 26 2022

.ANALYSIS AND UPPER LEVELS...

An upper-level ridge extends roughly from Kodiak Island east
across the Southern and Eastern Mainland, and a large dome of high
pressure remains stationary over the Gulf of Alaska. As a result,
widespread marine stratus continues to blanket the entire Gulf
and Southcentral coast, including Prince William Sound, Kodiak
Island, and Cook Inlet. The low clouds are also spread across the
western Kenai Peninsula (except Homer) and from Anchorage north
into the Mat-Su this morning. The remainder of Southcentral
continues to see generally clear skies.

Out west, a deep trough continues to dig in behind the ridge over
the eastern Bering while its associated surface front pushes into
the ridge and stalls over southwest Alaska. Thus, clouds and
rainfall dominate the Alaska Peninsula and coastal Southwest this
morning. Gusty southerly winds also persist across the eastern
Bering and for Southwest coastal locations. Widespread fog and
low stratus cover the Bering and Aleutians, keeping skies overcast
and visibilities reduced for many locations across the region.

&&

.MODEL DISCUSSION...

Models remain in excellent synoptic agreement through Monday
afternoon, and overall forecast confidence through that time is
high. For the rest of the weekend, all models depict an upper-
level ridge lingering over Southcentral and the Eastern Mainland
while a trough digs in behind the ridge over the eastern Bering
and southwest Alaska. By Monday night, however, model agreement
begins to diverge as the main upper trough exits to the northeast
over the Mainland. The synoptic pattern becomes a bit messy with
the development and exact placement of some weak features,
including a shortwave ridge over Southwest for Tuesday morning.

&&

.AVIATION...
PANC...Light westerly winds will persist through the
TAF period. A marine layer has once again extended into Anchorage
early this morning, dropping ceilings to IFR/LIFR. Expect
IFR/LIFR ceilings to be predominant through early-mid afternoon
today, with brief clearing again Sunday afternoon and evening.
Visibility is also reduced this morning due to smoke from
wildfires and patchy fog. MVFR visibilities are expected through
at least this morning and could persist into the afternoon.

&&

.FIRE WEATHER...

Southcentral: The main fire weather concern will be the Copper
River Basin, where hot and dry conditions will prevail for the
next few days. Convection looks quite limited, with the best
chance for a shower or thunderstorm along the Wrangell Mountains
and Alaska Range (the northern to eastern basin). Thunderstorm
activity will likely increase on Tuesday due to increased ridging
aloft and associated low level warming/increased instability.
Lacking a significant short-wave aloft, think lighting activity
will remain below Red Flag thresholds, but this bears watching.
While the rest of Southcentral won't see any rain, the influence
of the marine layer will maintain cooler temperatures and higher
RHs for the next couple days, before hotter and drier conditions
return on Tuesday.

Southwest: General cloudiness will continue with southerly flow across
Southwest Alaska. Wetting rain chances remain the greatest along
the coast and where upslope terrain enhancement is possible on the
windward side of the mountain ranges across Southwest and the
AKPen. Dillingham, west towards Togiak and Cape Newenham are
expected to have the most moisture. While there is a chance of
precipitation on the leeside of these mountains, areas such as
Bethel and King Salmon will generally be downsloped and thus lower
QPF is expected. Winds will be gusty today and potentially
stronger than they were yesterday for locations a little more
inland. Areas to the east of the Middle Kuskokwim Valley and the
valleys of the Western Alaska Range could be similar to yesterday
with temperatures in the 70s and RHs in the upper 20s to 30
percent. Although it is not expected to be as warm or dry, it is
still possible to have breezy conditions to stay alert to fire
weather concerns for that area.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Tuesday night)...

A stagnant pattern will lead to steady state conditions across
much of the forecast area the next couple days, very similar to
the weather observed on Saturday. The marine layer, in the form
of low clouds and patchy fog, will prevail this morning along the
coast as well as up Cook Inlet into Anchorage and portions of the
Mat-Su. The sun will ultimately burn this off, leading to a late
afternoon surge in temperatures. The marine layer will then surge
back in tonight and we'll see a repeat on Monday. Areas far enough
inland to escape the marine stratus will experience much warmer
temperatures with full sunshine. The only chance for precipitation
will be in the Copper River Basin, primarily along the Wrangell
Mountains and Alaska Range where conditions will be unstable
enough to trigger isolated to scattered afternoon/evening convection.

For Monday night and Tuesday, it looks like pattern will shift
just enough to cause some changes in weather. A building ridge
over Southwest Alaska will lead to development of weak low level
offshore flow over Southcentral. This should both prevent a strong
onshore surge of marine stratus Monday night and clear out and
remaining low clouds along the Gulf coast and Prince William Sound
on Tuesday. A return to mostly sunny skies combined with the
offshore flow will lead to warmer temperatures in the 70s to
lower 80s. Meanwhile, the upper high sitting over the Yukon will
drift back toward the Copper River Basin. This will lead to low
level warming and an increase in instability. As a result, expect
an increase in thunderstorm activity.

&&

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

Strong, southerly flow continues today across Southwest Alaska
with a Bering Sea low to the west and high pressure to the east.
Plenty of moisture is also continuing to stream northward
maintaining cloudy skies and precipitation. Highest POPs and QPF
are closer to the coastlines and locations on the windward side of
terrain enhancement which can help rain out the precipitation.
Areas to the lee of the mountains could have periods of rain, but
mainly expect some degree of downsloping and thus comparatively
much lower accumulation of rainfall. Winds could be gustier than
they were yesterday but tonight, expect winds to gradually
decrease through late Monday morning. Further inland near the
Western Alaska Range, warmer and drier conditions continue
relative to the coast. Monday night into Tuesday, a weak ridge may
build in from the east to help decrease precipitation and weaken
overall flow across Southwest. The details around this timeframe
for the interior becomes more unclear but another wave from the
Bering low may begin to press onshore again Wednesday.

&&

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

Broad area of low pressure is stalled over the Bering Sea for the
next few days. As the low dips southward, energy associated with
the low will redirect flow to increase winds and POPs through the
Central Aleutians Sunday. Winds will increase as they become more
southerly and will strengthen throughout the day Monday towards
the Pribilofs to around 30 kts. The upper jet streak will continue
to strengthen going towards midweek. Winds are expecting to peak
late Tuesday morning for the Pribilofs. Because this low is
generally stalled out the Bering, the eastward progression of this
wave will break down by midweek. POPs will follow along this
front across the Aleutians and the Pribilofs and it too will begin
to breakdown midweek.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

Bering Sea/Aleutians: A low crosses the Aleutians into the
Southern Bering on Wednesday. Its front extends across the
central Aleutians and moves into the eastern Aleutians by
Wednesday morning. Good confidence in a few localized gale force
gap winds possible with this front. Wednesday night, a second
North Pacific low crosses into the Bering and pushes its front
across the central and eastern Aleutians through Thursday.
Moderate confidence with southerly gale force winds along this
front. Seas remain below 20 feet.

Gulf of Alaska: With high pressure in place over the Gulf, winds
below gale force and seas less than 20 feet are expected for the
days 3 through 5 period.

&&

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

Looking ahead into the extended, ensemble guidance continues to
trend towards upper level ridging with higher heights to be the
story for Southcentral Alaska for the period. Although, there
appears to be reasonable deterministic agreement that a shortwave
will cross into the region from the southwest (Barren
Islands/Kodiak area) during the day on Wednesday. Most
precipitation and convection associated with this wave should be
confined to the favored upslope areas and higher terrain of the
Alaska Range/Talkeetna Mountains/Copper River Basin. The ridge
will slowly migrate east during the latter half of the period with
heights falling. However, confidence diminishes with exact timing
and evolution of additional upper level shortwaves moving through
the flow and frontal passages late week through the first half of
the holiday weekend. The odds favor that Southcentral will
continue to experience warmer than normal temperatures during the
extended period with slight chances of above normal precipitation
a change from the dryness over the past month.

For Southwest Alaska, there is good deterministic agreement of an
upper shortwave passing through Bristol Bay which could spark some
showers in the favored upslope areas of the Ahklun Mountains and
Western Alaska Range for Wednesday. Ridging nudges back in from
the south for Thursday with guidance hinting at quieter weather.
Guidance then hints at a more unsettled second half of the
extended period (Thursday night through Saturday) with onshore
flow and influence from an upper level low pressure system in the
Bering Sea. Confidence is low to average with exact timing and
evolution of the synoptic features such as associated shortwaves
and frontal passages. In general, expect continued unsettled,
rainy, and gusty weather for the Bering Sea and Aleutian Chain as
an active storm track remains throughout the area.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
MARINE/LONG TERM...DN