Gale Warning 358, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 PM AKDT Thu Apr 28 2022

.ANALYSIS AND UPPER LEVELS...

High pressure is building into the Gulf of Alaska today which is
bringing southerly flow into Southcentral Alaska. Flow aloft over
Southwest Alaska and most of the Bering Sea is from the southeast.
This is a result of an elongated surface low over the Aleutian
Islands which will consolidate into a fairly strong low in the
central Bering Sea tomorrow. This elongated low can be seen on
satellite with the clouds moving from the east just north of the
Aleutians and from the west just south of the Aleutians. There is
another front of note extending out of the North Pacific and over
the Alaska Peninsula into the eastern Bering Sea. This front is
bringing rain to much of the Alaska Peninsula this afternoon. The
jet stream is running in mostly zonal flow just south of the
Aleutian Islands.

&&

.MODEL DISCUSSION...

Models are all in good synoptic agreement through the weekend even
with the complex pattern of the low development and progression
from the Bering Sea into the Gulf of Alaska. Models are keeping
the northeastern Copper River Basin as the only area that could
see any diurnal shower activity the next few days.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 3...Tonight
through Sun afternoon)...

Mostly quiet, near seasonable, and dry weather are expected for
much of Southcentral tonight and Friday as an upper level high
pressure system remains overhead. The only exception might be some
of the mountainous terrain where an isolated pop-up rain/snow
shower will be possible late this afternoon/evening and again on
Friday afternoon/evening. The activity across the Copper River
Basin Friday might be more robust and a little more widespread
than today as an upper level shortwave (easterly wave) moves from
east to west.

Next, a front associated with a low pressure system over the
southcentral Bering continues moving eastward along the Aleutian
Island Chain and AKPEN tonight through Friday. This will mark the
beginning of a pattern change across the area, especially for the
Prince William Sound and eastern Kenai Peninsula areas. Expect a
fairly unsettled period of weather for Kodiak Island over the
weekend with periods of moderate and at times heavy rain as the
front moves through. Rainfall totals are expected to range from 2
to 3 inches with locally higher 4"+ amounts in surrounding
mountains. There will also be increasing gusty easterly/east-
northeasterly winds leading to a wind-driven rain. As the front
lifts northward, expect high end gale force winds through the
Barren Islands area and storm force gusts. Expect much of the same
through the Gulf of Alaska as the high end gale force front lifts
northward towards the North Gulf Coast Saturday/Saturday evening.
Expect some areas of storm force gusts as well. Also, expect
increased seas of 15-20 ft as the front lifts north over the
weekend. Much of Southcentral will remain on the downslope side of
the system due to deep southeasterly flow while the coastal areas
of the Kenai Peninsula and Prince William Sound will see steadier
precipitation. Most of the precipitation is expected to remain
over the mountains but there is the risk of a sprinkle or very
light shower that moves into the Cook Inlet region over the
weekend.

Also with the southeasterly flow and increased pressure gradient
against the Chugach Mountains, this will lead to a Turnagain Arm
wind Friday afternoon/evening. However, right now this is
expected to mostly remain out over the Arm and then bend down
Cook Inlet on Saturday and Sunday as down inlet flow develops.
There may be a brief time Friday afternoon/evening that a weak
southeast wind may make into West Anchorage and Ted Stevens
International Airport but generally 10 kts or less.

&&

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

Southwest Alaska is located beneath the western periphery of a
high pressure system which is expected to keep most of the region
dry through Friday. Cloud cover and rain showers will increase in
coverage and southeasterly winds steadily increase tonight ahead
of a series of fronts approaching the Southwest coast. Rain
showers are initially expected to be widely scattered outside of
areas of higher terrain, though more widespread coverage is
likely, accompanied by the strongest winds, along the Southwest
coast as the front moves onshore Friday afternoon. Winds will
diminish near the coast on Friday night as the front slowly works
its way inland. Gusty winds will continue further inland over
Southwest Alaska through Saturday as the front stalls and weakens.
Saturday night, a developing low in the Gulf of Alaska will cause
winds to shift northerly and a return to drier conditions for
Sunday.

&&

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

A developing low centered near Atka will be the main feature of
concern across the Bering Sea/Aleutians through Saturday. South
to southeasterly winds along its front will ramp up tonight over
the eastern Bering/Aleutians. By Friday morning, winds increase to
gale force along the Southwest coast and south of the AKPen.
Widespread rain showers are expected along the frontal boundary as
well, with the heaviest precipitation along the southern side of
the AKPen. Light rainfall will also persist across the Central
and Eastern Aleutians through Saturday morning. As the low
occludes and weakens Friday night, its associated front weakens
and moves inland, with winds diminishing and precipitation along
the Aleutian chain decreasing in coverage. Saturday night, a North
Pacific low will approach the western Aleutians, bringing
moderate-to-heavy rain as its front pushes east along the island
chain. This round of heavier rain reaches the eastern Aleutians
and southern AKPen by Sunday.

&&

.Marine (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska: Expect widespread small crafts and periods of gales
along the north Gulf coast through Tuesday. High-end gales are
expected late Saturday into early Sunday as a front extends across
the Gulf. After a lull, a weakening low will push towards the
northern Gulf Monday morning, increasing winds to lower-end gales.
As a broad low crosses the AKPEN early Tuesday, its front will
bring another swath of gales into the north Gulf coast. Some
uncertainty persists with the finer details in the timing and
strength of these winds. Seas about 12 feet increase to near 20
feet where gales are expected.

Bering: A strong low tracking along the Aleutians will bring
widespread small craft winds and areas of gales. Easterly winds
across the Bering will become northerly as the low continues
moving east into the Gulf. Gusty, northerly gap winds are expected
south of the Eastern Aleutians and AKPEN on Tuesday. Seas up to
16 feet in the Bering and up to 22 feet in the North Pacific.

&&

Long Term Discussion (Days 4 through 7: Monday through Thursday)...

With the jet stream winding near Southern Alaska and a longwave
trough overhead, expect unsettled weather to continue through the
extended period. Good model agreement at the synoptic scale
persists through Wednesday, with minor differences in timing and
other finer details. For Southcentral, the week will begin with
wet and windy conditions along the coast. First, a vertically
stacked low moves into the northern Gulf Monday morning, bringing
rain and enhanced winds along its front. Another vertically
stacked low makes its way into the Gulf Monday afternoon,
reinforcing winds and rain along the coast. Rain will linger along
the north Gulf coast into Wednesday as this second low weakens
and drifts across the Gulf. Model agreement deteriorates into
Wednesday regarding the descent of a shortwave from the Arctic.
The GFS shows the shortwave moving through Southcentral, In
contrast, the Canadian and Euro put the shortwave in Southwest
Alaska, with the Euro showing a weaker solution. The eventual
location of this shortwave will have implications on precipitation
potential and where gustier winds and lower temperatures should
be expected.

For Southwest Alaska and the Aleutians, the week will begin with
a low transiting along the Aleutian Chain and into the Gulf.
While winds will be elevated, the strongest winds will remain
further south in the North Pacific. Rain will slowly taper off by
Tuesday as the low moves into the Gulf. However, northerly winds
behind the low will keep gusty gap winds a concern along the
Alaska Peninsula and Eastern Aleutians through Wednesday. From
Wednesday through Thursday, weak high pressure builds in. Models
hint at a North Pacific low moving towards the Western Aleutians
Wednesday, though agreement is poor regarding its evolution. While
the GFS suggests the low will persist through Thursday, the
Canadian and Euro are quicker to have it dissipate.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 130 131 150-170 172 174 176 180 181 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
MARINE/LONG TERM...MK/KC