Gale Warning 422, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 AM AKDT Sat Jul 23 2022

.ANALYSIS AND UPPER LEVELS...

Little change overall to the synoptic pattern has occurred
compared to yesterday, as a large, stacked low remains stationed
in place over the Seward Peninsula. The middle to upper level flow
has become notably more zonal across the southern mainland, with
a 105 kt upper level west-east jet axis now expanding from the
eastern Bering across the Alaska Peninsula into the northern Gulf.
The more westerly flow and subsidence/drying behind a negatively
tilted shortwave lifting up into the northern Copper Basin and
Alaska Range has yielded partial clearing over parts of
Southcentral between Friday afternoon and this morning,
particularly from the Cook Inlet and western Kenai Peninsula up
into parts of the Mat-Su Valleys. Moisture left behind from
earlier rainfall and still seasonably cool midlevel temperatures
and the resulting weak instability are still helping to support
light, widely scattered showers over mainly the Prince William
Sound, Susitna Valley and Copper Basin vicinity.

Out west, most of the active weather is now focused over the
Aleutians, where a pair of shortwave troughs are moving swiftly
east within a broad envelope of cyclonic flow associated with the
northern Bering low. These two systems are sending periods of rain
and easterly winds to around 25 mph across the Aleutian Chain this
morning, with some of the more moderate rainfall now spreading
from the eastern Aleutians into the southern Alaska Peninsula. The
rest of the Bering and Southwest are seeing calmer conditions,
with some breaks in the low cloud cover persisting from parts of
Bristol Bay into the central Bering.

&&

.MODEL DISCUSSION...

Models continue to stay in good agreement for the first 48 hours
of the forecast period, however significant issues have emerged
with the evolution of a low expected to deepen as it moves across
the central Aleutians Sunday morning and up into the eastern
Bering through Monday morning. The overall consensus for the
intensity of the surface low with this system has backed off
markedly compared to model projections from around 24 hours ago,
with especially the 0z NAM and GFS now showing the lowest central
pressure bottoming out 10 to 15 mb higher (around 990-995 mb
instead of about 980 mb) compared to their earlier respective
runs from late Thursday to Friday morning. Only the Canadian model
is holding onto a stronger low becoming wrapped fully in gale
force winds over the eastern Bering by Monday morning at this
juncture. It appears the central issue at play is the interaction
between two separate shortwaves, one currently located over
northern Kamchatka, and the other now moving into the western
Aleutians. Most solutions have backed off on the expected phasing
of the two waves, and have delayed the eventual merge to several
hours later on Sunday compared to the earlier solutions showing
the more rapid deepening by around this time. This is resulting in
a notable challenge for the wind forecast on the west domain. The
concern for winds peaking near storm force range is lurching
suddenly to doubt as to whether the low will even manage to
support sustained gale force winds.

&&

.AVIATION...

PANC...VFR conditions are expected to mainly persist through
Sunday morning, but scattered lower clouds around 3000 to 4000 ft
along with a few sprinkles may persist early this morning. Strong
and gusty winds are expected to pick up out of the Turnagain Arm
from the southeast by around noon today, then peak in intensity
during the afternoon. Gusts to near 30 kts will be possible at
times over the terminal this afternoon. Winds will rapidly
diminish this evening as the stronger winds bend out of Anchorage
to the south, with a light northerly wind setting in for the rest
of the TAF period through early Sunday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Monday night)...

A shift in the overall flow the next couple days will bring a break
in rain to much of Southcentral. For today, a series of weak short-
waves lifting northward across Southcentral will exit northward
across the Alaska Range. A few light rain showers will linger, but
the bulk of Southcentral will be dry with some breaks of sun. The
next system of interest is the surface low tracking just south of
the Alaska Peninsula. A near zonal upper level jet will keep this
low to the south, passing south of Kodiak Island tonight then
weakening as it crosses the Gulf of Alaska on Sunday. Rain and
wind will be confined primarily to Kodiak, the Gulf coast, and
Prince William Sound regions as the low passes through later
today through early tomorrow. Surface ridging out ahead of the
low will lead to gusty gap winds, namely Turnagain Arm into
Anchorage, Knik River Valley into Palmer, and along the Copper
River into Glennallen.

Sunday will start out dry, with possible breaks of sun once again.
However, a digging trough over the Bering Sea and deepening low
headed for Southwest Alaska will lead to increasing clouds and
some areas of light rain later in the day. Conditions will
continue to deteriorate Sunday night through Monday as the upper
trough shifts eastward, pushing a frontal system eastward over
Southcentral and the Gulf along with a strong upper level jet
streak and associated fetch of deep moisture transport. As a
result, expect the return of widespread rain Monday-Monday night.
Given the high amplitude upper level pattern combined with the
track (northward across western Alaska) and strength of the
surface low, there will be quite a bit of wind with this system as
well. Strong S-SW winds will primarily serve to enhance
precipitation along the south sides of mountain ranges while east-
west pressure gradients will lead to strong southeasterly gap
winds. Most noteworthy, there is potential for 50 to 55 mph gusts
along the upper hillside of Anchorage Sunday night into Monday.
While these types of winds are typical during the fall and winter
storm seasons, it is much less common to see those kind of winds
in late July.

&&

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

Cool, showery conditions continue today across Southwest today
and tonight. Southeast gap winds will pick up today across
interior Bristol Bay as a front moves into the Gulf of Alaska and
pushes air flow through Kamishak gap. The next system pushes
towards the Southwest coast Sunday night through Monday. There is
still quite a bit of model uncertainty with this system, with
solutions going back and forth on strength and speed of the low as
it tracks towards Southwest. As a whole, expect continuous
rain showers and increased winds across the region Sunday night
through Monday. Winds should begin to decrease again Monday
evening. Increased sustained winds raise concern for high surf
potential for Bristol Bay and the Kuskokwim Delta. There is still
uncertainty for how strong the storm surge will be, but coastal
flooding is looking less likely at this time.

&&

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

Overall, benign weather conditions along the Bering and Aleutians
through tonight. The next system moves into the southern Bering
on Sunday night and pushes towards the Southwest coast through
Monday. There has been a fair amount of inconsistency with this
system, but expect winds to push into or near gale force and seas
to build to 8 to 12 feet. Additionally, expect areas of moderate
to heavy rain showers through Monday night.

&&

.MARINE (Days 3 through 5: Monday through Wednesday)...

Gulf of Alaska: There's moderate confidence of gales in the
western Gulf, through the Barren Islands and along the Gulf coast
Monday associated with a storm out to the west. Seas should remain
between 10 and 15 feet with these winds. There is a possibility
of westerly gales through Kamishak Gap on Tuesday as the storm
moves through the area, but confidence is low. An additional front
extending northeast from a North Pacific low may clip the
southern Gulf on Wednesday, but confidence is low.

Aleutians/Bering:

Forecast confidence for a gale force low in the eastern Bering is
moderate late Sunday into Monday; however, there is still uncertainty
in the exact strength/placement of the low and it's speed of
progression inland. This will effect the duration of southwesterly
gales in Bristol Bay as well as subsequent increase in wave
height. Wave heights to the west of the low center may reach up to
20 ft, particularly south of the Pribilof Islands. Regardless,
the low will move inland late Monday, which should bring gales to
an end. Later on, there is moderate confidence of a front moving
over the Western Aleutians on Wednesday, which may reach gale
force.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

Cooler and wetter than normal conditions can be expected into the
beginning of next week as a large, vertically-stacked low
continues to be centered near the Bering Strait through Tuesday.
Its front sweeps eastward across Southcentral, continuing the wet
and rainy trend, with showery, cooler conditions closer to the
center of the low over Southwest Alaska. Models finally eject this
low into the Arctic Ocean by Wednesday, with indications that
shortwave ridging will take its place over southern mainland
Alaska, allowing the region to dry out mid-week. However, with
flow remaining southwesterly, any embedded shortwave troughs could
provide the instability for intermittent rounds of showers or even
stratiform rain. Models key in on one particular feature which
tracks into the western Gulf on Wednesday or Thursday which is
likely to bring rain to coastal regions of the Gulf and Kodiak
Island. The track and timing of this feature remains uncertain at
this time, though, with minimal model agreement on the details.
This will impact whether more interior portions of Southcentral
continue to see further rainfall throughout the week or see a
reprieve. By the end of the week, there is also broad agreement
that a North Pacific low crosses the Aleutian Islands into the
Bering Sea and pushes its front as far as the Southwest coast by
late Friday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 131, 138.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...CJ/CQ