397
FXAK68 PAFC 111250
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 AM AKDT Sat May 11 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Monday night)...

A large vertically stacked low is drifting eastward along the
Alaska Peninsula and toward Kodiak Island this morning. A leading
occluded front extends from just north of Kodiak Island south-
southeast across the western Gulf and is lifting north and east.
East to southeast winds are strengthening ahead of the front
along the north Gulf coast and into Prince William Sound. These
winds extend across the Kenai Peninsula, strongest through Portage
Valley and other east-west oriented valleys. Short-waves along the
east side of the low are tracking northward right toward the Kenai
Peninsula, leading to moderate rainfall along the southeastern
coast. Rainfall is much lighter as you head to the interior Kenai
Peninsula due to some downward motion off the coastal mountains.
Light rain also extends to the southwestern Kenai Peninsula
(Kachemak Bay/Homer area) and to eastern Prince William Sound
(Cordova/Valdez areas). Snow levels range from roughly 1000
to 1500 feet above sea level. Webcams show some snow through
Turnagain Pass, but it is not accumulating on the roadway. Dry,
but cloudy conditions can be found across the remainder of
Southcentral. Localized gap winds persist, most notably in the
Matanuska Valley and Copper River Valley.

The low will continue to track slowly to the east-northeast,
reaching the northern Gulf tonight, with the occluded front
dissipating as it pushes onshore. Winds and precipitation along
coastal areas will diminish tonight, with precipitation becoming
more showery with time. The upper low will open into a trough as
it heads inland across the southeastern Copper River Basin and
into the Yukon on Sunday. This will leave a weak trough over
Southcentral for Sunday. With a fairly moist airmass in place and
increasing instability as some breaks develop in the clouds cover,
it looks like a favorable day for some scattered afternoon/evening
showers. As is typically the case, expect the bulk of these along
or near the mountains.

Weak ridging will build overhead on Monday while a weak low tracks
south of Kodiak and into the Gulf. Kodiak will see a quick shot of
light rain. There still could be some afternoon/evening convection
in Southcentral, but with a lack of upper level forcing and weak
instability expect shower coverage to be more isolated in nature.
Temperatures will incrementally warm as we head through the next
few days, with increasing sunshine and overall moderation of the
chilly airmass currently in place.

-SEB

&&


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

A stacked low embedded in a longwave trough stretching across the
western Mainland and Bering Sea is now drifting about halfway
between Chignik and Kodiak Island this morning. Areas of mainly
rain near sea level are continuing to drift around the low into
the AKPen and Bristol Bay regions, but most of this activity is
staying rather light and spotty. Out along the Aleutians, a weak
low moving south of the Chain is extending its front into the
area, producing bands of light rain and easterly winds in small
craft advisory range this morning.

The weak North Pacific low and attendant front will continue to
push steadily east through Sunday, eventually working into the
southwest corner of the Gulf by Sunday night. Behind this feature,
quiescent conditions (by Bering Sea standards) will overspread
much of the Bering as a stout upper ridge moves into place. The
break won`t last long, however, with a strong Kamchatka low set
to push a warm front into the western Bering by Monday night.
This will be a system to keep an eye on over the next day or two,
as it may end up pushing unseasonably strong winds and high waves
into much of the Bering Sea as it moves east early next week.

Turning attention to Southwest, not much change to the pattern is
expected over the next couple of days as the low entering the Gulf
slowly drifts east and weakens in place. Expect a return to more
pleasant but still mostly overcast conditions today as
temperatures climb into the 50s over interior valleys. Afternoon
showers will develop with daytime heating, especially close to
the low center towards Bristol Bay this afternoon where cooler air
aloft is in place. Offshore flow will weaken between Sunday and
Monday as the low to the southeast continues to fall apart and the
ridge over the Bering Sea starts to encroach in from the west.
Afternoon shower activity will continue both days, especially
closer to the Alaska Range. While far from certain, there may be
just enough instability developing on Sunday afternoon to support
a couple thunderstorms forming near the western Alaska range and
Lower Kuskokwim Valley. This thunderstorm potential will be
heavily dependent on how much cloud cover is able to clear out
during the afternoon and allow for more ample solar heating.

-AS

&&

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

The Alaska weather map opens with an elongated and somewhat
fragmented positively tilted trough extending from the Arctic over
the Eastern Mainland. The trough then curves back to the South of
the Alaska Peninsula. The Northern portions drifts into the
Canadian Provinces through Wednesday, while the Southern portion
links up with a second system moving out of the Russian Far East.
The trough becomes negatively tilted for Thursday, with an
increasing negative tilt through Friday. A ridge builds over the
ALCAN border through Friday. Model agreement is good through
midweek, but falls apart afterwards, as the flow pattern across
the region weakens.

The extended forecast opens somewhat quietly as North Pacific low
moves the active weather into Southeast Alaska. In the far West,
the Northern Kamchatka low and front brings gusty winds and
precipitation starting as snow, but quickly changing to rain
across the Aleutians and Bering. The front brings locally heavy
precipitation over the Central and Eastern Aleutians, AKPEN and
Western Alaska. Some of this will be mixed precipitation over
Western Alaska into the Interior, and trailing through Wednesday
before diminishing over the AKPEN Thursday. Locally heavy rainfall
moves moves over Kodiak Island and Southcentral Alaska for
Thursday and across Prince William Sound and Copper River Delta
through Friday. Lesser amounts of rainfall from the South reaches
the Alaska Range for Friday.

- Kutz

&&

.AVIATION...

PANC...VFR conditions will prevail through the TAF period as
downslope flow maintains dry conditions in the lee of the Kenai
and Chugach Mountains. During the morning hours, southeast winds
out of Turnagain Arm will remain over the Arm and bend down the
inlet coincident with the strong north to south gradient between
the low pressure system over the Alaska Peninsula and higher
pressure over the Mat- Su Valleys. There is a slight chance that
southeast winds may clip the terminal towards this afternoon as
instability increases and low- level lapse rates steepen with
daytime heating. The caveat to this will be if cloud cover
persists over the Mat- Su Valleys which will inhibit instability.
Regardless, the gustiest of the southeast winds should remain over
Turnagain Arm and the most likely scenario is light and variable
winds for the terminal this afternoon/evening.

&&

$$