Gale Warning 305, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 PM AKDT Mon Apr 18 2022

.ANALYSIS AND UPPER LEVELS...
The main weather feature remains the large low centered near
Unimak Pass this afternoon. The front over the Alaska Peninsula is
producing southeasterly gusts in the 35 to 50 mph range with wind
gusts farther west over the central Aleutians around 45 to 60 mph.
Effects of this system reach the western Gulf of Alaska where
easterly flow is brining in some clouds and a few snow and rain
showers to Kodiak Island today.

The upper level pattern over mainland Alaska has shifted a little
since late last week with the 500 mb ridge now closed off along
the Arctic coast and a weak upper low in the Northeast Gulf of
Alaska. This upper low will strengthen a little and drift westward
the next few days. Some of the change in seasons can be seen over
the western Kenai Peninsula where the land is heating enough to
cause some fair-weather cumulus clouds to develop as until they
reach the colder waters of Cook Inlet and then dissipate again.

&&

.MODEL DISCUSSION...
Models remain in good synoptic agreement through the week. The
main differences in the ALeutians during the middle of the week
are beginning to resolve in the latest model runs. A newer feature
that is creeping into the second half of the week in Southcentral
is a 500 mb closed low moving in from the east. This was
indicated as an open wave earlier, but models are all now
indicating it will be a little stronger and be a closed upper
level low for Wednesday night into Friday so that is a little bit
of a change that could bring in clouds and a greater chance for
some showers as well.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3: Tonight through Thursday)...

Relatively quiet weather conditions are expected to persist across
much of the region for the next few days. With generally clear
skies and weak daytime heating, a light afternoon/evening sea
breeze is expected to occur for Kachemak Bay today, Wednesday and
Thursday. Onshore flow persists for the southeastern side of
Kodiak Island and is associated with a strong system out west over
the Aleutians. Thus, there are increased chances for
precipitation for southeastern Kodiak Island as a result of
southeasterly upslope flow against the mountains accompanied by
some weak disturbances aloft. As the Aleutian system tracks into
the southern Gulf through Wednesday and surface winds shift more
northeasterly, chances for precipitation decrease for the island.

At upper levels, a ridge of high pressure that has dominated the
region for the past few days is now being replaced by a series of
easterly waves and general low pressure. Lingering high pressure
over northern Alaska has created a weak offshore gradient with the
low pressure across Southcentral, yielding blustery northeasterly
winds through areas like Thompson Pass and the Matanuska Valley.
Offshore flow is expected to diminish on Wednesday as the high
pressure moves farther northward and the area of low pressure
with embedded disturbances spreads across the southern mainland.
This feature will essentially rotate over southern Alaska through
Thursday, and light isolated showers are possible across the
region.

The next feature of note is a front extending from a deep North
Pacific low. The front will push northeastward into the Gulf and
reach Kodiak Island late Thursday night. With this system,
precipitation at the surface is expected to be rain, and it will
spread across Kodiak Island and the north Gulf coast into the
weekend.

&&

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

A fairly tantamount weather pattern is expected over the
Southwest for the next couple days. Southeasterly winds and cloud
cover will persist along the coast with brief showers possible
over northern Bristol Bay and into the Kuskokwim Mountains. High
temperatures will be in the 40s with temperatures lowering to the
30s to upper 20s at night.

Tuesday will mark the beginning of a pattern change for the area
due to an easterly wave over Southcentral tracking over the
region. The forcing from this wave and daytime heating should be
enough to generate a few showers over higher terrain Tuesday
afternoon/evening. After the easterly wave passes through the
region, clearing skies and a more pronounced diurnal trend in
temperatures is expected.

&&

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

Active weather persists across the Bering Sea and Aleutians for
the next few days as a strong vertically-stacked low dominates
the area. The aforementioned low will exit north of Nikolski and
slowly track eastward with the center moving just south of the
Alaska Peninsula tonight. On the backside of the low, strong
northwesterlies are extending over the Central Aleutians with the
core of the strong winds slowly moving east towards the Eastern
Aleutians through today. High winds were observed this morning
over Atka with gusts reaching up to 63 mph.

The weather will quiet down briefly Tuesday before another
gale force North Pacific low moves near the Central to Western
Aleutians. Gale force winds with storm force gusts will impact the
Central Aleutians Wednesday as the low skirts just below the
Chain. Winds will diminish fairly quickly Wednesday evening, but
rain will sweep across the Chain along the storm's front starting
over the Western Aleutians and working its way eastward into the
Alaska Peninsula by Thursday.

&&

.Marine (Days 3 through 5: Thursday through Saturday)...
Gulf of Alaska: A deepening low pressure system will move
a weather front from the western Gulf Thursday to the northern
Gulf Friday. Easterly winds of 20 to 30 kt will develop Thursday
with low end gales up to 40 kt possible from the Barren Islands to
Kayak Island for Friday into early Saturday morning as a barrier
jet forms ahead of the front. Expect waves along the northern
Gulf to build to around 10 to 15 ft along the northern Gulf for
Friday in association with the gales. Forecast confidence for this
outlook is high.

Bering Sea: A north Pacific low south of the Aleutian Chain will
move east into the western Gulf through Friday. An accompanying
weather front will cross the eastern Aleutians and AKPen Thursday
before exiting the region Friday. Widespread high end small craft,
to low end Gales will extend as far north as the Pribilof Islands
and extend into Bristol Bay by Friday. Northwesterly gales are
expected along the backside of this low, with the core of these
winds channeled through the central and eastern Aleutians. Seas of
15 to 20 ft are expected across the southern Bering with seas of
20 to 25 ft possible on the Pacific side of the central and
eastern Aleutians through Friday morning. Seas will subside to 10
ft or less late Friday through Saturday. Forecast confidence for
this outlook is high.

&&

Long Term Discussion (Days 4 through 7: Friday through Monday)...
An upper-level ridge over the northern half of the state will
weaken and shift to the southwest as an upper-level low moves east
from the Aleutians and extends a shortwave north toward the
Southern Mainland. At the surface, this translates to a weakening
of the ridge over the state as a surface low moves from south of
the eastern Aleutians Friday to the southern Gulf of Alaska late
Saturday through Sunday. An occluded front attached to the low
will sweep across the western and northern Gulf, bringing an
increase in rain and winds first along the AKPen and Kodiak Island
Friday then along the Southcentral coast through Saturday. Weak
ridging out ahead and north of this system, along with a cross-
barrier flow, should limit precipitation for inland locations,
although an increase in cloud cover through the weekend is likely.
This system then weakens and drifts southward late Sunday into
Monday with a general clearing trend from north to south across
the region.

Farther west, a ridge will build across the Bering and Aleutians
through the weekend in the wake of the low, resulting in a cool,
northerly flow across the Aleutian Chain. The ridge extends over
the western half of the state by Sunday and over the Southern
Mainland for Monday. A weak upper-level wave and associated
frontal system tries to move over the top of the ridge by Monday
with scattered precipitation for the Kuskokwim Delta possible. A
second weak surface low may impact the western Aleutians and
Bering for Monday as the ridge moves over the Mainland.

Temperatures across the region are expected to remain around average,
but will warm through the latter half of the weekend as the ridge
moves over the state and any lingering cloud cover from the Gulf
low diminishes.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 170 172-174
         Gale Warning 150 155 160 165 171 175-178 180 412-414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...AF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
MARINE/LONG TERM...TM