Gale Warning 317, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
448 AM AKDT Fri Apr 1 2022

.ANALYSIS AND UPPER LEVELS...

A broad longwave trough extends from the western Bering eastward
to the Gulf of Alaska with the main jet stream (core inside of the
jet exceeding 160+ kts) remaining south of the Aleutian Island
Chain. Embedded in the longwave trough is a strong upper level low
currently present to the east of Kodiak Island along with two
other weaker and smaller upper level lows over the northwestern
Bering. Another strong upper level low is present across the
Northwest Territories with weak upper level ridging present across
the Copper River Basin with this ridge extending northward into
the Arctic Ocean. Southeasterly flow is present over Southwest
Alaska in between the broad longwave trough over the Bering and
the weak ridging over interior Alaska.

The aforementioned upper level low was bringing a steady rain
(moderate to heavy at times) to Kodiak Island including Kodiak
City through the evening and overnight hours. This low was also
bringing storm force winds peaking around 60 kts to the Barren
Islands area during the evening and through the overnight hours.
Amatuli Island had a peak gust overnight of 60 kts. Some of the
moisture associated with this low was making it over the
Aleutian/Alaska Ranges and through Kamishak Gap into Southwest
Alaska, in particular, Bristol Bay resulting in occasional light
rain/snow showers. Snow showers were most prevalent from Pilot
Point south. Generally benign weather was occurring across much of
the Bering with occasional snow showers for the Aleutian Island
Chain and the Pribilof Islands.

&&

.MODEL DISCUSSION...

Models remain in good agreement on the synoptic scale features
out through Day 3. Models are in good agreement on the movement
and placement of the current upper level low just east of Kodiak,
therefore, minimal changes made this to part of the forecast.
Slight differences begin to arise towards the end of Day 2 heading
into Day 3 (Sat afternoon through Sunday) on the exact track
placement of another surface low moving northwards towards the
eastern Gulf of Alaska for the weekend. However, the GFS was the
more favored model on the eastern side with the forecast more
geared towards this model. The other models show similar things
with slight changes in terms of pressure and placement but these
are expected to have minimal impact to the overall forecast. The
NAM was the furthest west model and weakest while the other models
GFS/Canadian-NH/and EC were clustered around the same general
area across the eastern Gulf.

&&

.AVIATION...

PANC...VFR conditions are expected to persist throughout the TAF
package. Northerly winds through around mid afternoon (~01/22z)
are expected to shift to southeasterly as the Turnagain Arm wind
bends into the terminal for a couple of hours with gusts up to 20
mph. During the evening ~02/04z, winds are expected to become
light and variable before becoming northerly 5 to 10 kts again
overnight around ~02/12z.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3; Today
through Sunday)...

The Gulf low is just east of Kodiak Island early this morning and
is on track to move over the island and make it into Bristol Bay
this afternoon. This will cause the winds to shift as the low
passes overhead with northerly winds this morning turning
generally to the southeast by the afternoon. The periods of
moderate rainfall should mostly be ending during the morning but
the rain will continue throughout the day.

The main front associated with this low is stretched along the
north Gulf coast this morning and pushing slowly northward. Due
to the low's track it will be rather slow top move through. While
most of the precipitation will downslope out along the coastal
mountains, the big uncertainty is whether this front will turn
winds southeast behind it for a period of time today in the
Anchorage and Matanuska areas. The passage of a front to the
north generally will have the winds follow the lower pressure with
it and turn southeast, however the front is not strong and the
low near Kodiak is keeping a northeasterly flow down Cook Inlet
so it will be a delicate balance as to where the Turnagain Arm
winds will go. In the Matanuska Valley the question is whether the
Matanuska River winds will switch to a Knik River wind due to
this.

For the weekend, a low developing well south of Kodiak today will
move into the southeastern Gulf of Alaska and remain quasi-
stationary. This will keep cold air aloft over all of Southcentral
with some weak shortwaves rotating around the low bringing in some
rain and snow showers. The low will be far enough south that there
is also a good chance for some breaks in the clouds for inland
areas as well both Saturday and Sunday.

&&

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

A low moving over Shelikof Strait is bringing isolated rain/snow
showers along the coast. Much of Bristol Bay remains dry with
downsloped southeasterly flow. More widespread showers are
possible over this area by evening if easterly model solutions
verify, bringing the center of the low closer and thus eliminating
the downsloping component. In any case, precipitation will remain
light. Scattered snow showers will continue tracking up the coast
through Sunday as the low slowly moves northward over the eastern
Bering.

&&

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

A low will track into Bristol Bay through today. Snow will
develop across the eastern Aleutians in a northwesterly flow this
evening. Gusty winds up to 30 mph may lead to periods of reduced
visibilities. Conditions will gradually improve overnight into
Saturday morning as the low dissipates. A strong upper jet
extending across the North Pacific is allowing for the development
of a deeper upper trough which will bring widespread snow showers
to develop and persist through the weekend across the entire
Bering/Aleutians.

&&

.MARINE (Days 3 through 5 - Sunday through Tuesday)...

Gulf of Alaska - A well developed Southeastern Gulf low moves to
the North Central Gulf by Tuesday. Forecast confidence is mixed
with the timing. Gusty Easterly Winds increase to high end gales
over the Northern Gulf for Monday, then diminish. Seas build to
15 feet, subsiding. Gusty Westerly winds across the Southern Gulf.
Seas building to 16 feet Tuesday.

Bering - An Eastern Bering low moves inland Monday. Its front
weakens over the Bering by Tuesday. A frontal wave tracks Eastward
to the South of the Aleutians by Tuesday. Forecast confidence is
mixed with the Bering front. Gusty West winds ahead of the front
become Northerly through Tuesday. Seas less than 10 feet.
Widespread high end Westerly gales with the frontal wave remain
South of the Aleutians through Tuesday, diminishing Monday. Seas
to 18 feet on the Pacific side of the Western and Central
Aleutians, subsiding.

&&

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

Overall, the latest operational model runs are in good agreement
with the evolution and progression of the synoptic scale features,
but begin to diverge in the specific details towards the end of
the period. As an upper level high retreats from the northwestern
mainland to the Chukchi Sea, a broad upper level trough over the
Bering Sea/Aleutian Islands extends eastward across the Gulf and
over Southcentral Alaska. This amplified pattern should persist
particularly over western Alaska through the short term. Ensemble
means are decently clustered with this synoptic pattern in the
medium range period before increasing uncertainty emerges for the
middle of next week. At the surface, a low near the Kuskokwim
Delta coast weakens further on Monday, while a couple of stronger
systems are expected to track across the North Pacific into the
Gulf. Even though there is a good amount of discrepancies and
variability with these systems, most of the precipitation will be
concentrated through the Panhandle and up into the southern
coasts. Much of the mainland should be relatively dry with
seasonable temperatures during the period, with the exception for
potential snow in the mountains and colder inland areas.

Out west, an active storm pattern associated with the
aforementioned trough will maintain showery conditions and gusty
winds for much across the Bering and Aleutians into early next
week. Beyond Tuesday, however, models seem to struggle with the
differences of the upstream flow from Siberia to Kamchatka. This
will play some role in the timing and strength of surface features
near the Alaska Peninsula and Bering region. The EC builds a
ridge in the western Bering, while the GFS/Canadian carries a low
that tracks over the Aleutians and a separate low near the
Panhandle through the Wednesday/Thursday timeframe.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 120 130 131 138 139.
FIRE WEATHER...NONE.

&&

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