587
FXAK68 PAFC 021336
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
536 AM AKDT Thu May 2 2024

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

GOES imagery shows a large upper-level low currently across the Gulf
of Alaska and far northeast Pacific Ocean. The axis of precipitation
along the front currently stretches from the north Pacific into
Kodiak Island and across the Kenai Peninsula. Rainfall amounts over
the last day have ranged from approximately 0.8" in Kodiak to 0.6"
at a RAWS site south of Kenai Fjords NP. Farther west, strong
low/mid-level southeast flow has downsloped across the mountains and
resulted in much of the western Kenai northwards considerably drier.
The 00z AFC sounding sampled this well, showing dry air in the
lowest 4000ft of the atmosphere, with abundant moisture / clouds
above.

The weather the next few days will be largely the same as the last
24 hours. Precipitation across Kodiak Island and the Kenai Peninsula
will taper off this evening as the parent low shifts southeast.
However, in true Alaska weather fashion, another low and associated
front will quickly move into the place of the existing system on
Friday into the weekend. Precipitation will pick back up for Kodiak
and the coastal Kenai Range, with everywhere north/west of the
mountains largely maintaining dry, though cloudy, weather given the
downsloping flow. Temperatures will be near climatological averages,
though with nights slightly warmer than average due to cloud
cover.

-Brown

&&


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

A weakening front continues to lift into Southwest Alaska,
producing some light rain along the northern Bristol Bay coast this
morning. Returns on the King Salmon radar suggest widespread
virga across Bristol Bay but surface observations are only
intermittently recording precipitation at the ground in the
vicinity of Dillingham. Precipitation will gradually wind down
through the day associated with the front, though some isolated
showers are forecast to develop across portions of Southwest
Alaska this afternoon/evening. Otherwise, Southwest Alaska remains
mostly dry until the arrival of the next front from the Bering Sea
on Friday.

This front, pushing into the central Bering Sea/Aleutians this
morning, is bringing rain and gusty southeasterly to easterly
winds to these areas. This afternoon, the front pushes into the
eastern Aleutians while its parent low lags behind, just beginning
to track into the western Aleutians, where it will bring more
showery rainfall. The low, however, is accompanied by relatively
colder air aloft (850 mb temperatures around -6 degrees C), which
means that as the front and low advance steadily eastward, the
Pribilof Islands are likely to see snow beginning late tonight.
Through Friday, 2 to 4 inches of wet snow are likely in Saint
Paul and Saint George. By Friday afternoon, the front reaches
Southwest Alaska, leading to more significant precipitation
chances and cooler temperatures than have been seen with the
current, weaker front moving through the area yesterday and today.

Of particular note will be the relatively cooler air associated
with the low. As the front lifts north through Southwest Alaska,
colder air will arrive from south to north, with warmer air
remaining in place over Interior/Western Alaska. This will mean
that though precipitation begins as rain on Friday, by Friday
night precipitation will switch over to snow for some parts of
Bristol Bay for a time. The Kuskokwim Delta and Lower Kuskokwim
Valley will, at least initially, remain warmer and all rain as the
warmer air wraps around the north side of the low and out over the
northern Bering Sea. The front weakens for Saturday, allowing
precipitation to become more showery and colder air working north
will allow for some snow potential in the Kuskokwim Delta and
Valley. Precipitation gradually winds down through the weekend as
the low tracks into the Gulf of Alaska. Looking ahead to the
beginning of next week, there is a good chance a deep trough digs
over the northern Bering Sea, bringing cold air to much of the
Bering and dropping temperatures into the 20s and 30s for portions
of Southwest Alaska.

CQ

&&


.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 and light winds will persist.

&&


$$