Gale Warning 200, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
540 AM AKST Thu Feb 24 2022

.ANALYSIS AND UPPER LEVELS...

The upper level pattern remains highly amplified, with a sharp
longwave ridge continuing to make progress eastwards towards the
AlCan border. A large upper level low harboring several embedded
waves continues to spin in place near the western Aleutians, with
the strongest feature becoming an inverted trough and attendant
surface low pivoting towards the Kamchatka Peninsula. An long
fetch of southeast flow continues along a frontal zone situated
between the large scale ridge and trough aloft, with a roughly 40
to 60 kt low level jet in place above most of the Southwest as
sampled by a few remote area observation sites along the Aleutian
Range and western Alaska Range about 2,000-3,000 ft above sea
level. Gusty southeast winds continue even at the lower elevations
across the Southwest, particularly where funneled through the
Kamishak Gap out over Iliamna Lake and towards Koliganek where
gusts between 50 and 70 mph were observed overnight. Due to the
strong southeast flow, precipitation along and ahead of the front
has mainly been limited to areas favored by upslope enhancement.
This includes the windward faces of the Kuskokwim Mountains and
western Alaska Range, as well as western portions of the Kenai
Peninsula and Kodiak Island. It's been an especially wet a soggy
past day or so for Kodiak, where nearly 2 inches of new rainfall
was recorded on Wednesday.

&&

.MODEL DISCUSSION...

Models are remaining in good agreement overall with the
progression of the synoptic pattern over the next several days.
Some differences remain for the evolution of a strong upper level
low expected to move up from the North Pacific on Friday and
retrograde northwest into the Bering by Friday afternoon. The most
recent two runs of the NAM in particular begin to diverge from the
consensus shortly after the point where the low is projected to
cross over the Alaska Peninsula, with a slightly slower and
farther east track depicted for the low as it moves northwest just
offshore from the Southwest coast. This ties into some uncertainty
for strong winds expected to follow the low east of the center.
The GFS suggests winds could be strong enough to produce blizzard
conditions over parts of the Kuskokwim Delta early on Saturday if
surface temperatures manage to stay below freezing during the
period of strongest winds.

Two forecast challenges continue for Southcentral over the next
couple days as well. The first involves the expected heavy
rainfall for Seward, where it remains unclear how much a
relatively unfavorable east-west flow orientation across
Resurrection Bay will decrease rainfall totals in an otherwise
favorable setup for steady, moderate rainfall through Friday
night. The other challenge will be deciding whether warning level
(75 mph or greater gusts) will occur along the Turnagain Arm
during the peak of the strongest southeast flow across the Kenai
Peninsula and Prince William Sound early on Friday.

&&

.AVIATION...
PANC...VFR conditions and light north winds will persist. There is
some potential for low level wind shear to develop near or below
2,000 ft threshold as southeast winds increase aloft, especially
near the end of the TAF period on Friday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Thursday through
Saturday night)...

The first of a series of surface fronts has made the push to the
northern Gulf coast, stalling along the Southcentral coast
overnight. Broad southeasterly winds ahead of this feature are
ushering a deep fetch of moisture from the tropical Pacific
northward. This slug of moisture in wringing out over the
Southcentral coast in the form of rain along the immediate coast,
a rain/snow mix farther inland, and snow at higher elevations.

A second frontal system is moving into the western Gulf this
morning and will continue to track toward the northern Gulf by
late morning. This feature, along with an associated upper-level
wave moving northward in the southerly flow aloft, with help
enhance the precipitation, with rainfall along the coast (and
snowfall in the mountains) becoming steadier as the day goes on.

In addition to the rain, the push of each frontal system toward
the coast will ramp up gusty southeasterly gap winds, especially
through Turnagain Arm, as the pressure gradient between a coastal
ridge over eastern Prince William Sound and lower pressure to the
west tightens. While the winds will be quite gusty through
Turnagain Arm and across the higher elevations of the Chugach and
Kenai Mountains, gusts along the Upper Hillside of Anchorage are
not expected to be nearly as strong due to the orientation of the
pressure gradient bending the core of the strongest winds down
Cook Inlet. The gradient, however, will lend to occasional gusty
winds across the Matanuska Valley this morning and again Friday
morning.

Precipitation along the coast will increase in intensity late
Thursday into the first half of Friday as a third frontal system
associated with a storm-force low south of the AKPen lifts to the
northern Gulf. The Turnagain Arm winds will increase yet again,
peaking Friday morning before slowly winding down late Friday as
the low elongates and weakens as its parent low moves northwest to
the eastern Bering. This action will also allow the precipitation
to slowly taper off late Friday evening through Saturday morning.

Upwards of 5 to 8 inches of rain is expected for Whittier and
Portage Valley with 1.5 to 3.5 inches of rain for Seward through
Saturday morning. The western Kenai Peninsula and Anchorage Bowl
are expected to stay relatively dry through Saturday due to
downsloping from the strong southeasterly (cross-barrier) flow
running up against the Kenai and Chugach Mountains.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3 - Today
through Saturday night)...

A deep 960 mb upper low over the northern Bering is contributing
to substantial warm air advection from the Aleutians into
Southwest Alaska this morning. Its front extends over Saint
Lawrence Island down into interior Bristol Bay. Scattered rain
showers stretch from the Kuskokwim Delta into the Alaska
Peninsula. Morning temperatures across Southwest range from the
mid to upper 30's to as high as the low 40's across the peninsula.
The upper low over the northern Bering will continue northward
throughout the day on Thursday with precipitation coming to an end
for most areas by this afternoon. Later tonight showers will
resume with the arrival and passage of a strong, negatively tilted
upper trough. This trough is expected to cross the Alaska
Peninsula and lift northwestward into the Bering during the
overnight hours. Consequently, much of its precipitation will fall
offshore of the coast, though light snow will be possible for
coastal areas and as far south as Cold Bay. Colder temperatures
aloft will accompany the trough's passage with cold air advection
leading to intense easterly winds from the Kamishak Gap westward
into interior Bristol Bay through the morning hours and eventually
into the Kuskokwim Delta by Friday afternoon. Sustained winds of
up to 50 mph with higher gusts are currently forecast. One
forecast uncertainty is the potential for snow to fall across the
Kuskokwim Delta and coastal portions of Bristol Bay. Should models
trend any colder or further east with the trough, the potential
for blizzard conditions will increase due to the expected easterly
winds.

&&

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

Morning satellite shows the slow departure of a large upper low
over the northern Bering, with southerly flow across the Aleutians
maintaining warm air advection from Adak to Dutch Harbor. Morning
temperatures range from the mid 30's into the low 40's. Numerous
rain showers are noted across the Western and Central Aleutians as
a weak trough pivots through the region. Shower activity over the
Eastern Aleutians, however, is more limited. A trough of low
pressure south of the Eastern Aleutians will lift across the
Alaska Peninsula later tonight, which will keep shower chances
primarily east of the region. Through the next 24 hours colder
temperatures are forecast to filter into the Bering from the west
as a trough amplifies over the Eastern Bering during the overnight
hours. This will lead to rain changing over to snow on Friday
with light snow showers possible across the Aleutian Chain Friday
into the weekend with minimal accumulations. Strong pressure falls
ahead of the trough may promote easterly gales during the morning
hours across Bristol Bay while southwesterly gales will likely
follow in the wake of the low from the Alaska Peninsula through
Nunivak Islands late Friday into Saturday morning.

&&
Gulf of Alaska:
A front extending across the Northern Gulf moves onshore for late
Saturday. High pressure moves across the Gulf through Monday.
Forecast confidence is moderate. A high end gale force barrier jet
along the North Gulf Coast diminishes late Saturday. Seas to 20
feet, subsiding. A new front approaches the Western Gulf for Monday.

Bering Sea/Aleutians:
A well developed Central Bering low moves into the Russian Far
East for Sunday. A developing North Pacific low and front pushes
across the Western Bering by Monday. Forecast confidence is
moderate. Gusty winds surround the Central Bering low, with areas
of Southerly gales along the Eastern flank, diminishing Sunday.
Seas less than 10 feet. The Pacific low and front brings Southerly
gales, with areas of storm force winds over the Western Aleutians
and Bering. Seas build to 16 feet along the Pacific side of the
Western Aleutians by Monday.

&&

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

The longwave pattern will feature a broad trough over the Bering
Sea and much of Mainland Alaska. For the Bering, the negative
height anomalies at 500 mb persist through March 3rd. However the
situation is a little more complicated for the Mainland at 500 mb
as they transition from negative to positive. The Bering and the
North Pacific will be major areas of cyclogenesis this forecast
period. The models spin up a number of lows at the surface,
however there is some divergence regarding the tracks of the
surface lows and the intensities. However, all the models are
forecasting a busy period for the Northwest Pacific and the
Bering Sea. Some of this activity will move into the Gulf Of
Alaska. The predominately dry areas with the possibility of
intermittent light showers for this time frame will be Talkeetna
to Anchorage. High temperatures for the Anchorage Bowl and Mat-Su
Valleys will be slightly above freezing ranging from 33F-39F.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning: 119,130,131.
         Gale Warning: 120,125,132,137,138,139,140,351,352,150,
         160,165,180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
MARINE/LONG TERM...PS