Small Craft Advisory 593, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
542 AM AKDT Sun Jul 31 2022

.ANALYSIS AND UPPER LEVELS...

Two upper level low's will be prominent features through the early
week, with a high pressure ridge separating the two. The first low
is currently situated over the Western Aleutians, quickly making
its way eastward before pushing onshore over Southwest Alaska
Monday morning. The system will continue pushing east, crossing
over the Western Alaska Range and then shifting southeast to track
into the Gulf of Alaska. It will be the main weather driver for
Southern Alaska through Tuesday afternoon. The low will drift off
towards the Southeast Panhandle Tuesday night. An upper ridge
follows the first low and will provide a break in active pattern between
the two systems. The second low enters the western Bering Sea
Tuesday night, tracks towards Southwest through Wednesday night,
and is expected to bring unsettled weather back to the Southern
Mainland by Thursday.

&&

.MODEL DISCUSSION...

Models remain in good overall synoptic agreement through the short
term. There is a little bit of a timing issue when it comes to
precipitation, but overall it shows that the next system will
produce a good amount of rainfall. The next system enters the
western Bering on Tuesday night and there still remains some
inconsistency regarding the low center as well as the speed of the
low. As it stands now, the Canadian seems to be the fastest after
crossing the Western Aleutians while the NAM seems to be lagging
behind just a bit.

&&

.AVIATION...
PANC...Lower cloud ceilings will continue through the morning
hours, dropping to MVFR at times. Brief periods of light rain
showers are possible during the early morning hours. Conditions
are expected to improve to VFR by the afternoon.

&&

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

A vertically stacked low over the northeastern Gulf will continue
to produce light rain across eastern Prince William Sound and
towards Cordova this low will move east today and rain will come
to an end by mid-day. Meanwhile a weakening upper level shortwave
will produce small areas of light rain mainly from Anchorage to
the MATSU valleys. By afternoon the shortwave will dissipate as a
broad transitory ridge moves into the area with rain ending
across most valley locations. A few brief breaks in the clouds are
possible this afternoon and evening providing brief period of
sunshine. On Monday a strong low pressure system will bring
widespread rain across much of Southcentral. A surface low will
form across the northern Gulf but downsloping is not expected due
to the strong dynamics of this system. Monday night into Tuesday
the upper level low will track into the northern Gulf this will
keep rain going across most of the area through Tuesday morning.
By Tuesday afternoon the low will track east of the area with rain
ending across most of the area except the Copper River Basin
where rain will persist through Tuesday night. Gusty outflow winds
are expected to develop Tuesday as the low pushes east with Gale
force gusts expected near the Barren Islands and gusty winds
across Resurrection Bay and Passage Canal.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Tuesday night)...

Scattered showers continue across Southwest Alaska this morning,
with steadier rainfall near the Western Alaska Range expected to
taper off today as an upper-level trough exits to the north and
east. Despite a shortwave ridge transiting the region today,
scattered showers will linger area-wide with low-level synoptic
scale cyclonic flow remaining in place. This will combine with
persistent moist, onshore flow near the surface to keep the
environment supportive of unsettled weather across the Southwest.
However, a few breaks of sun will be possible, with slightly
warmer temperatures in the low to mid 60s for Sunday afternoon,
especially for eastern portions of the forecast area, stretching
from the northern Alaska Peninsula to the Western Alaska Range.

Somewhat drier conditions will be short-lived, though, as the
next system arrives along the Southwest coast Sunday evening,
bringing another round of wetting rains which will progress
quickly inland, reaching the Western Alaska Range early on
Monday. Despite the moderate intensity rainfall expected along the
front, the rapid eastward speed of the system will limit
accumulation over any one area, keeping rainfall amounts for
Sunday evening through early Monday afternoon between 0.2 to 0.5
inches. The highest amounts will be focused along the Western
Alaska Range, where southeast flow shifting to westerly and
upslope flow will prolong steady rain into Monday afternoon. The
rest of the outlook area should see rain taper off to widely
scattered showers from west to east beginning Monday morning for
the Kuskokwim Delta and late morning for the Lower Kuskokwim
Valley and interior Bristol Bay.

Shortwave ridging will again move into place behind the exiting
low pressure system starting Monday night, leading to partial
clearing and slightly rebounding temperatures back in the mid 60s
for highs on Tuesday. This ridge is expected to be more robust,
with surface high pressure building in through the day on Tuesday.
As a result, this should clear out shower activity more so than
with the present upper-level ridge. Some rain showers, however,
can be expected to persist on the western slopes of the Kuskokwim
Mountains and Alaska Range into Tuesday night.

&&

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

Active conditions continue across the Bering Sea into the
beginning of next week as two separate low pressure systems are
set to affect the region. The first of these systems is a fast-
moving low pressure system currently tracking across the western
Aleutians, and in the process of occluding. This low will continue
to bring rain and gusty winds across much of the Aleutian Chain
today as it enters the western Bering. Westerly gale force winds
will pick up through the Western and Central Aleutians this
morning as cold air wraps along the south side of the low. This
swath of gale force winds will track eastward along the islands,
reaching the Eastern Aleutians Sunday evening.

By Monday morning, winds on the south side of the low will weaken
below gale force as the area of strongest westerly flow moves
into the southern Alaska Peninsula and the low tracks inland over
Southwest Alaska. This should give way to a break from the wind
and rain on Monday as a shortwave ridge moves into place over the
Bering. However, the break will prove short, with the second low
and front expected to reach the Western Aleutians by Monday
evening. Model guidance tracks this low a bit slower than
previously, meaning rain and windy conditions, up to potentially
low- end gale force, persist for longer near the Western
Aleutians, with the center of the low tracking into the Bering and
front lifting across the islands Tuesday night.

&&

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

A broad upper low and front are progged to exit the eastern Gulf
on Tuesday. Gales associated with the low, if any, will be
confined to the far southern reaches of the Gulf early Tuesday.
High pressure then takes control of the region on Wednesday before
the next trough moves into the western Gulf early Thursday.
Potential southwesterly gales will be possible into the Shelikof
Strait as the trough first overspreads Kodiak Island, but quickly
weaken and become westerly Thursday afternoon. Offshore seas may
build to 10 feet on Tuesday.

Aleutians / Bering:

Gulf of Alaska: A Kamchatka low moves into the Western Aleutians
and western Bering Sea on Tuesday. The low is forecast push into
mainland Alaska on Thursday. Models are not depicting a
particularly strong area of low pressure. Nevertheless, areas of
gales may be possible on the south side of the low from the
Western and Central Aleutians into the Pribilofs through
Wednesday. Forecast confidence decreases by Thursday with timing
and placement of the low into the west coast of Alaska a bit more
uncertain. Seas to peak at 10 feet.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...

A longwave trough over the Bering Sea on Wednesday will promote
unsettled conditions from the Aleutians into coastal regions of
Southwest. Cyclonic flow around the base of the trough will favor
a track for embedded upper level disturbances to push across the
Aleutians into mainland Alaska, accompanied by scattered showers
and gusty winds. Additional clouds and rain will also result in
cooler temperatures across Southwest as the trough overspreads
mainland Alaska into Friday. Further east, shortwave ridging over
Southcentral will result in warmer temperatures and mild winds
Wednesday into Thursday. However, the eastward progression of the
aforementioned longwave trough over Southwest will ultimately find
its way into Southcentral by Friday. This will bring widespread
rain chances into Southcentral along with gusty conditions
offshore of the Gulf coast. Little relief is forecast on Saturday,
despite the departure of low pressure into Southeast Alaska, as a
new shortwave trough digs into Southcentral from the north. This
should allow for precipitation chances to linger into Saturday
while also maintaining cooler temperatures. Finally, models are
hinting at the arrival of yet another upper low into the Aleutians
by Saturday with potential gales and renewed showers.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 170 172-177
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
MARINE/LONG TERM...BL