Gale Warning 304, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
524 PM AKDT Sun Apr 17 2022

.ANALYSIS AND UPPER LEVELS...

An upper-level ridge remains in place across interior Alaska and
extends down to the Gulf of Alaska. A polar trough has moved south
from the Yukon Territory and has undercut the ridge from the
east. The expanse of low stratus underneath the ridge has
diminished in the wake of the trough and with the cooler, drier
airmass advecting in behind it. Clouds have given way to generally
clear conditions from the northern Susitna Valley to the Copper
River Basin and Prince William Sound. However, with the trough
stalled in an area from Skwentna to Middleton Island, clouds
persist across areas south and east of these locations. Scattered
clouds and isolated showers also persist across portions of
Southwest Alaska this afternoon as a weak upper-level wave moves
over the southwest coast.

Farther west, a potent upper-level low and associated surface low
are moving across the western and central Aleutians. These
features strengthened overnight, aided by a strong 160 kt jet
streak over the north Pacific. A warm front associated with the
mature surface low is nearing Nikolski this afternoon.
Southeasterly ahead of the front are increasing, with gusts near
50 kt reported. Gusty winds are also persisting across the
western Aleutians with winds starting to ramp up across the
Pribilofs.

&&

.MODEL DISCUSSION...

Models remain in good agreement through the next few days leading
to above average forecast confidence. There are some minor
discrepancies in the progression of weak waves rotating around an
upper-level trough over the Southern Mainland for Tuesday into
Wednesday. However, these differences are not too impactful,
mainly determining the expanse of cloud cover and shower activity.
Out west, some differences appear in the position of a Kamchatka
low moving south of the western Aleutians. The GFS and NAM keep
the center of the low south of the Chain while the GEM and EC
bring the low over the central Aleutians by Wednesday. The
position of this feature will determine the extent of winds and
precipitation across the Aleutians through midweek.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. The 6,000 ft
ceiling is expected to scatter out by late afternoon or evening
and continue to diminish through the overnight hours.

&&

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

The main synoptic feature over Southcentral is associated with an
Arctic shortwave trough pushing southward from the AK-Yukon
Territory. Pressure gradient driven northerly winds continue to
funnel through Glennallen and into Thompson Pass, with higher
gusts at times. As the shortwave moves further south into the
coastal waters, some showers are possible along the higher terrain
of the eastern Kenai Peninsula through Monday morning. Meanwhile,
a moist, southeasterly flow forming along and ahead of a frontal
boundary near the AKPEN will bring light showers across Kodiak
Island beginning late tonight through Wednesday.

Otherwise, a ridge of pressure will build over the northern
mainland, while the aforementioned trough shifts over the southern
mainland. Expect mostly clear skies with daytime temperatures in
the upper 40s and overnight lows ranging in the 10s and 20s.
As we head into the middle of next week, easterly waves
pinwheeling on the backside of the trough crosses over from the
Copper River Basin into the Mat-Su Valley. However, given the
limited instability and snowpack in the mountains, little or no
precipitation is expected for the low-lying regions and higher
terrains.

&&

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

Relatively quiet weather conditions are expected to persist for
Southwest for the next few days. Much of the region is currently
cloud covered. Beginning Monday morning, strong southeasterly
winds will develop along the Kuskokwim Delta coast, Bristol Bay,
and Alaska Peninsula as a strong Bering Sea low passes out west.
Winds are expected to diminish Monday night as the low tracks
southward into the North Pacific. Beyond this time and through
Wednesday, interior Southwest is expected to see clear skies while
Bristol Bay and the Alaska Peninsula will likely stay cloud
covered.

&&

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

Active weather persists across the Bering Sea and Aleutians for
the next few days as a vertically-stacked storm force low
dominates the area. The low is centered over the southern Gulf
near Adak this afternoon while its front pushes eastward across
the central and eastern Aleutians, into a downstream ridge. Deep
southeasterly and northwesterly flow maintains widespread storm
force winds ahead of and behind the low, respectively. Ahead of
the low and with the front, the strongest core of winds crossed
Dutch Harbor and the eastern Aleutians during the day today and
are now reaching the southern part of the Alaska Peninsula. Winds
will be especially gusty through any gaps and passes along the
eastern Chain and Alaska Peninsula, such as Cold Bay, King Cove,
and False Pass. Winds will continue to spread up and along the
peninsula before slowly diminishing through the day on Monday. On
the back side of the low, northwesterly storm force winds in cold
air advection continue, and the strongest core of winds will cross
the central Aleutians tonight and slightly weaken Monday mid-
morning. However, winds will quickly strengthen again and persist
into Tuesday morning as an upper-level shortwave tracks southward
across the central Aleutians, mixing down stronger winds. Thus, a
High Wind Warning remains in effect from this evening through
Monday afternoon for the central Aleutians, where gusts up to 75
mph are expected. With this large system, precipitation is
expected to be primarily rain, although a rain/snow mix may be
possible for the Pribilofs and colder areas along the back side of
the low.

Widespread precipitation and winds diminish on Tuesday as high
pressure builds in from the west and east, forcing the low to drop
southward into the North Pacific. Another strong system will move
from the Pacific towards the western Aleutians by Wednesday
morning and will then track eastward along the Chain through
Wednesday. Current model runs do not illustrate great agreement
with the exact placement of the low center, so areas of most
likely impactful weather conditions have yet to be ironed out.

&&

.Marine (Days 3 through 5: Wednesday through Friday)...

Gulf of Alaska: Calm to light conditions will persist across most
of the Gulf Wednesday. Seas will generally remain below 5 ft. On
Thursday and Friday, a deepening low pressure will move a weather
front across the Gulf from West to East. 25 to 30 kt will peak on
Friday for areas near Prince William Sound. Low end Gales of 35 to
40 kt winds and seas increasing to 10 to 15 ft will peak Friday
Morning. A weak barrier jet is anticipated late Friday. Forecast
confidence for this outlook is high.

Bering Sea: A north Pacific low will move just south of the
Aleutian Chain through Friday. An accompanying weather front will
cross the central Aleutians Wednesday evening and will move east
through 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 anticipated on the
backside of this low, impacting the central Aleutians the most.
Seas of 15 to 25 ft are expected across the southern Bering. Seas
of up to 30 ft are possible on the Pacific side of the central and
eastern Aleutians.

&&

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

High pressure across the state will slowly be replaced with a weak
inverted trough as the work week comes to a close. A strong north
Pacific low will remain south of the central and eastern Aleutians
as it weakens and moves to the southern Gulf of Alaska through
Sunday. Accompanying this low is a weather front that will bring
rain and winds to the Aleutians and across the Pacific facing
coast of Alaska. Cloud cover should be a mainstay as this low
pressure system moves through the region, expanding from west to
east. By Friday afternoon and into Saturday, rain will span from
Kodiak Island and stretch through Seward and western Prince
William Sound. Anchorage and the MatSu should remain relatively
dry due to the drying aspects of cross barrier flow, though an
occasional light shower in the mountains is not out of the
question. Temperatures across the region will be around average,
but will warm as the weekend approaches. Despite the cloud cover,
the warm air mass will allow temperatures to reach anywhere from 3
to 10 degrees above normal for late April. Clearing skies on
Sunday could allow daytime highs in Anchorage and Kenai to be in
the lower 50s, while the Mat Valley may reach the middle to upper
50s.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 187.
MARINE...Storm Warning 170 172-177 414.
         Gale Warning 150 155 160 165 171 178-181 185 411 412 413.
FIRE WEATHER...NONE.

&&

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