000
FXAK68 PAFC 200011
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
411 PM AKDT Fri Apr 19 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/This
afternoon through Monday afternoon)...

Few major changes to the previous forecast, though forecast rain
amounts continue to drop for Kodiak Island this weekend. Kodiak
Island continues to experience the highest impact weather, with a
Flood Advisory in effect for Kodiak City and surrounding areas,
while a Flood Watch remains in effect for the remainder of the
island.

Diving into the details... a large vertically stacked low
continues to spin south of the Alaska Peninsula and Kodiak Island,
embedded within a high amplitude negatively tilted trough which
extends well down into the Northeast Pacific. In between the
trough and ridge is deep strong southeast flow, with an
atmospheric river pointed right at Kodiak Island and the
northwestern Gulf of Alaska. A stationary front is positioned over
the southwestern Gulf just south of Kodiak Island. Heavier rain
today will taper off by evening as the responsible shortwave
trough continues past Kodiak and towards Southwest Alaska.

From tonight through Saturday, there will be a fundamental change
in what has been a stationary pattern. The upper level trough in
the Pacific will continue to dog all the way toward the Northwest
CONUS, cutting off the atmospheric river. At the same time, the
upper level ridge will begin to retreat to the north and east,
allowing winds to weaken at all levels of the atmosphere.
Therefore, by Saturday a much weakened front will be positioned
over the southern Gulf and Kodiak Island with much weaker upper
level short-waves embedded in the flow across the Gulf. Kodiak
Island will still see periods of rain tonight through Saturday
night, but intensity will be light. Thus, the threat of flooding
and landslides will diminish greatly as we head through the
weekend. By Sunday, multiple short-waves along with the remnants
of the current upper center will all morph into a newly formed
upper low south of Kodiak Island. Precipitation will become more
showery, with some breaks from the rain.

Meanwhile, the upper level ridge will continue to produce warm and
dry conditions over nearly all of Southcentral. The only exception
is the southern Kenai Peninsula, which will remain along the
northern periphery of the precipitation shield. Cloud cover has
been extensive the past couple days. However, as the upper trough
digs across the northeast Pacific and becomes more negatively
tilted, flow between the trough and ridge will back toward the
east. This will help clear out clouds for all except the Kenai
Peninsula, bringing a return to sunny skies. The upper level
ridge over Mainland Alaska will weaken on Sunday, allowing the
upper low and trough over the Gulf to lift northward toward
Southcentral. Overall, models are trending towards less impactful
weather with this system. While the corresponding surface low
looks to bring winds of about 25 kt to Gulf waters for Monday, as
well as increasing cloud cover and precipitation chances along the
coast, a progressive upper level pattern looks to push the system
east before it gets too close to the Southcentral Alaska coast.

-SEB/KC

&&

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

A shortwave associated with the low south of the Eastern Aleutians
continues to move west over the Pribilof Islands, where a Winter
Weather Advisory for blowing snow is currently in effect through
this evening. Precipitation along the Alaska Peninsula and
westward to Dutch Harbor will subside later tonight as the
shortwave weakens. Gusty winds for Southwest Alaska will continue
through tonight before a new shortwave moves north into the area.

The new shortwave will provide another round of precipitation for
the Bristol Bay area into Saturday afternoon before the wave
moves west into the Bering. The Pribilof Islands will again get
snow showers before the shortwave dissipates Saturday night.
Consistent onshore flow along the Eastern Aleutians will allow
for showery precipitation to occur through Sunday afternoon.
Moisture associated with the atmospheric river over Kodiak Island
will continue to move over Southwest through Sunday, providing the
chance for precipitation in the meantime.

The next main area of concern will take place over the far Western
Aleutians, as a shortwave low from the North Pacific and an
upper-level low from eastern Russia interact Sunday morning. The
two systems will phase together north of Shemya and develop into
a mature low over the western Bering. An occluded front from the
low will begin to move eastward Monday morning as widespread gale-
force winds and heavier precipitation will spread over the
Aleutians and Central Bering through Monday evening. The majority
of precipitation along the Aleutians should be in the form of
rain as warmer southerly air surges northward. The Pribilof
Islands may get a rain/snow mix, and areas near the low center
will likely stay as snow with colder air wrapping in behind the
front.

-BS

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through
Friday)...

A pattern shift is expected as we go into the weekend with the
synoptic pattern breaking down. Sunday into Monday, a strong low
develops as it moves into the western Bering Sea that will track a
front eastward next week. While the pattern is expected to break
down leading into the long term forecast, high pressure will
remain somewhat stubborn over Canada and stretching into the
interior of mainland Alaska. The strength and placement of the
ridge will influence the direction of the upstream flow. Expect
unsettled weather to continue through next week. Periods of rain
spread across Southcentral Alaska through Wednesday from the Kenai
Peninsula to the Canadian Border.

Additional subtropical moisture will be drawn into the developing
western Aleutian low early next week. Heavy precipitation will
spread across the Aleutians beginning as rain and transitions to
snow. Cold air wrapping into the low will help reinforce the
potential for strong, storm force winds. The influence of the
front appears to stretch into the northern Bering, affecting the
Pribilofs and St Matthew.

Potentially heavy rainfall continues to spread into the Alaska
Peninsula with the front through Tuesday, and into Southwest
Alaska late Tuesday and Wednesday. Another round of locally heavy
rains moves into Kodiak Island late Tuesday through Thursday.
Gusty, southeasterly winds moves through the Barren Island into
Kamishak Bay Wednesday and Thursday. Some of the moisture could be
diverted south depending on the interior ridge, but heavy
precipitation remains possible and the amounts will depend on
whether there is additional support from a secondary trough
phasing with the front. Model agreement also breaks down towards
the end of the week.

rux

$$

.AVIATION...

PANC...VFR conditions and light winds will persist.

-CC

&&
$$