Gale Warning 382, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
509 AM AKDT Mon May 15 2023

.ANALYSIS AND UPPER LEVELS...

Southwesterly flow in the upper-levels is beginning to encompass
Southcentral Alaska this morning. A positively tilted trough digs
southward from the Bering Sea into the North Pacific and is
anchored by an upper-level low south of the eastern Aleutian
Chain. The associated surface low is located over the extreme
southern Alaska Peninsula and is entering the eastern Bering. As
such, and with deep southerly flow out ahead of this low, rain is
observed all along Bristol Bay, the Kuskokwim Delta, as well as
the lower to middle Kuskokwim Valley. Meanwhile, an upper-level
ridge extends northeastward from the central Bering to the
northeastern Bering. The Pribilof Islands observe scattered mid-
level clouds/ceilings under mostly westerly flow in the upper-
levels as the ridge axis draws near. The western and central
Aleutians observe mostly northwesterly flow in the upper-levels as
a trough begins to dig southward into the far northwestern Bering
from the Gulf of Anadyr.

&&

.MODEL DISCUSSION...

Guidance is in overall good agreement with synoptic features
through the short-term period. There is more agreement now in the
limited eastward extent of precipitation for coastal Southcentral
Alaska on Tuesday as a trough lifts northward through the Gulf to
coast. While places like Cordova will still receive
precipitation, the more enhanced precipitation looks to stay
confined to central and western Prince William Sound. While the
00z GFS, NAM, and ECMWF agree on this idea, the 00z Canadian is
the eastern outlier with bringing more enhanced precipitation into
Cordova. Guidance is also improving on the handling of the
progression of the Bering Sea low as well as it looks to across
the Alaska Peninsula and into the eastern Bering this afternoon.
The forecast challenge remains timing out the more enhanced
bursts of precipitation outside of the upslopes of mountain ranges
for mainland Southwest Alaska.

&&

.AVIATION...

PANC...VFR conditions will persist. Southeasterly Turnagain Arm
winds will also persist. While gusts will be somewhat lower this
morning, anticipate them picking back up quickly during the middle
to late morning hours. Gusts, like yesterday, could approach 30 kt
before easing up again during the evening and overnight. Again,
like yesterday, there is also an outside chance of getting a
reading or two of around or at 35 kt; but confidence is low for
that. While VFR conditions are anticipated for the TAF period,
there is a chance for light showers Tuesday morning as a front
lifts northward from the southwestern Gulf of Alaska to the
northern Gulf Coast. With this frontal progression, Mid-level flow
looks more southerly as opposed to southeasterly in which case
downslope drying would most likely occur. Thus, given this more
southerly mid-level flow, along with south-southwesterly flow in
the upper- levels, there is opportunity for a few light rain
showers to make their way over the terminal for Tuesday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Today through Wednesday Night)...

A persistent weather pattern will bring yet another day of
generally dry conditions across interior Southcentral and
scattered showers along the coast. South to southeasterly gap
winds through Turnagain Arm, the Knik River Valley, and the Copper
River Basin, will continue, with another peak in the gusts
expected through Monday afternoon and evening before diminishing
Monday night.

By Monday evening, an upper trough and front will move into the
western Gulf of Alaska, with rain overspreading Kodiak Island.
The trough and attendant frontal system moves toward the Kenai
Peninsula for Tuesday morning with increasing low clouds and
areas of light rain likely from coastal Southcentral northwest to
the Susitna Valley. The trough and surface front then begin to
fall apart Tuesday afternoon as both lift northward. Winds behind
the front will transition from a southeasterly gap wind to a
southwesterly up-inlet flow. Any lingering precipitation will
transition to scattered showers, falling mainly along the upslope
areas of the Talkeetna Mountains and Alaska Ranges. Broad
southwest flow and seasonably cool conditions will continue into
Wednesday, except perhaps towards the Copper Basin, where the
upper ridge may begin to build back into place and allow
temperatures to warm into the 60s across interior valleys. High
pressure over the Gulf of Alaska may also produce areas of fog
over the coastal and offshore waters, as well as along the coast
of Kodiak Island for Wednesday.

&&

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

The elongated front currently stretched across Southwestern
Alaska and the Alaska Peninsula is expected to stall as high
pressure remains strongly in place to the east. The tilt of this
front will gradually become slightly more negatively tilted and
may even retrograde some as it interacts with an upstream cut off
low over the Central Aleutians and becomes more cyclonic near
Nunivak Island Tuesday. Cool air sitting across the Bering Sea
could become entrained into the front as these features interact.
Surface observations along the coast, such as Kipnuk, received
snow this morning and while surface temperatures will warm during
the daytime, a generally cool regime is expected for the next
couple days. Tuesday morning could be the coolest day for
Southwestern Alaska, when some locations could see some snowflakes
mix with rain or a transition completely over to snow during the
morning. Accumulations are not expected. The main issue though
will be this lack of forward progression and embedded shortwaves
that would lead to prolonged precipitation and winds across the
Alaska Peninsula and Southwest Alaska for the first half of this
week. The Kuskokwim Delta, northern Bristol Bay area, and the
windward side of the Alaska Peninsula will see the highest amounts
of precipitation during this time due to onshore, upslope flow. A
degree of downsloping along the lee of the Aleutian Mountains
will keep storm totals reduced on the northern side of the Alaska
Peninsula to King Salmon. Tuesday night through Wednesday,
precipitation will gradually become less widespread, but model
agreement begins to decrease around this timeframe.

&&

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

Forecast confidence for the extended period continues to be lower
than average. However, there look to be no major concerns during
this time frame.

Diving a bit more deeply into model talk, disagreement seems to
center around how quickly a ridge in the far western Bering
weakens on Thursday, and how the upper level low behind it will
interact with two other upper level features converging just south
of Mainland Alaska: a broad low extending across much of Western
Alaska and into the North Pacific, as well as a low lifting north
into the eastern Gulf. There is decent agreement between the
Canadian and ECWMF models that the ridge will be strong enough to
prevent the low behind the ridge from interacting with the other
two features. The GFS is an outlier in weakening the ridge enough
that all three features interact. As this major model
disagreement occurs early in the extended period on Thursday,
model agreement continually worsens through Sunday.

Still, a few general ideas can be gleaned even with poor model
agreement. Models seem to agree on ridging across Eastern Alaska
through at least Saturday; though confidence is low, there is a
potential for thunderstorms to form in the Eastern Alaska interior
on Friday and Saturday as shortwaves move along the ridge.
Meanwhile, southeasterly flow will likely lead to showers along
the north Gulf coast. There is greater uncertainty for Southwest
Alaska and the Bering/Aleutians. Going with the Canadian and ECMWF
consensus, a broad surface low south of Kodiak/Alaska Peninsula
will likely lead to northerly winds across the region and showers
moving into the Aleutians.

&&

SYNOPSIS AND MODEL DISCUSSION...DAN
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...KC

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
322 PM AKDT MON MAY 15 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0200 PM     FLOOD            NAPAIMUTE               61.53N 158.68W
05/15/2023                   BETHEL             AK   DEPT OF HIGHWAYS

            FLOODING, WATER OVER RUNWAY AND UP TO 4FT
            INTO THE HANGER. HOUSES WITHIN THE COMMUNITY
            ARE NOT CURRENTLY INUNDATED, BUT WATER IS UP
            TO HOUSES AND/OR SURROUNDING STRUCTURES.

&&

NS