325
FXAK68 PAFC 012350
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
350 PM AKDT Wed May 1 2024

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

Cloudy conditions will continue across Southcentral through the
end of the week and into this weekend as weak shortwaves move
through. A low exits the Bering Sea and moves into the southern
Gulf of Alaska on Thursday and its associated front pulls
moisture right towards Kodiak, eastern Kenai Peninsula, and
western Prince William Sound. The bulk of the precipitation will
be in the aforementioned areas for Thursday and Friday before
spreading eastward to include Cordova and Valdez by late Friday
night. The next system is taking a more southerly track and moving
a bit slower than shown in previous model runs that will delay
rainfall to Valdez and Cordova until at least late Friday night.
Additionally, easterly flow near Seward will help keep rain
lighter with lower amounts expected. Rain will be near continuous
for Kodiak Island through much of Thursday. Rainfall amounts in
Kodiak City should be around an inch to inch and a half, with
higher amounts in the mountains. Downsloping easterly flow will
keep the west side of the Peninsula and Anchorage largely dry.
Showery activity is possible today in portions of the Susitna
Valley and Copper River Basin but should remain light and brief.


&&


.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Friday night)...

A rapidly weakening low pressure system in the southeastern
Bering Sea continues to push a fairly weak frontal boundary into
Southwest Alaska this evening. Areas of light showers will persist
for the Bristol Bay region tonight before coming to an end
Thursday morning, as the parent low is absorbed by a stronger
incoming trough entering the western Bering tonight.

To the west, a new low pressure system is set to begin moving
over the western Aleutians by early this evening. The low will be
preluded by a front on the eastern leading edge. The front will
push quickly across the western-most Aleutians, reaching Adak by
late tonight/early Thursday morning. Initially, gale-force
southeasterly winds with light-to-moderate rainfall are expected
to be produced along the front, gradually weakening to sub-gale
and light rainfall by the time the front reaches Atka. By Thursday
afternoon, the front will have reached Nikolski, and the parent
low-pressure system will be entering the western Aleutians,
bringing another round of rainfall. The front and low will
continue advancing steadily across the Chain until the front
reaches Southwest Alaska by early Friday afternoon. Notably, as
the front crosses the Pribilof Islands late Thursday night/early
Friday morning, there is the chance for some of the early precipitation
to come down as a wet snow or a rain/snow mix. This is expected
to be brief, and accumulated snowfall would likely melt by Friday
afternoon. However, up to 2 inches of this wet snow is possible
before shifting to rainfall.

-CL

&&


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

Active, but not overly impactful weather, is expected for the
long term forecast. Generally, expect widespread precipitation
for the Southern Mainland as an occluding low dissipates in the
northern Gulf. An upper low moving from the Arctic into the Bering
Sea will bring a cool down for Southwest Alaska early next week.
By the latter half of Monday, this upper low phases with another
low in the North Pacific, strengthening it as it moves towards the
Southern Mainland through midweek. However, model agreement
diminishes considerably around Monday, leading to lower confidence
in the evolution of this system.

Diving into the details... Sunday begins with a broad longwave trough
extending across much of Alaska. A vertically stacked low over
Southwest Alaska will gradually move into the northern Gulf
through Sunday. The low`s front will bring steady rain along the
north Gulf coast, with inland areas in Southwest and Southcentral
staying much drier due to downsloping. Instead, these inland
locations will likely see widespread showers due to robust
vorticity associated with this upper low, with the potential for
stronger convection Sunday afternoon and evening as an easterly
shortwave transits the Copper River Basin. Otherwise, expect
outflow winds to pick up Sunday across Alaska Peninsula and around
the Gulf.

By Monday, a rather compact upper level low slides south from the
Bering Strait into the Bering Sea, drawing down colder air for
Southwest Alaska. While a bit chillier than what we`re seeing now,
overnight lows remain relatively high at around 20-30 degrees for
Southwest Alaska. Precipitation generally tapers off across the
region on Monday as the Gulf low dissipates and moisture remains
relatively limited for the Bering Sea low.

By Tuesday, poorer model agreement leads to lower forecast
confidence. The main point of contention between models is how the
Bering upper low phases with an upper low moving towards the
Aleutians from the North Pacific. For the forecast, have leaned
towards the consensus where these two lows phase, leading to a
strengthened surface low with stronger winds and higher moisture
content as it moves towards the Southern Mainland for Wednesday.
The alternate scenario keeps the surface low weaker, with much
less impactful weather expected. Neither scenario looks
particularly hazardous, but we`ll continue to monitor trends and
refine forecast details in the coming days.

-KC

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period.
Southeasterly Turnagain Arm winds are expected to pick up again
this afternoon and move over the terminal before diminishing
tonight. Winds thereafter should remain light and become northerly
by Thursday morning.

&&


$$