296
FXAK68 PAFC 100025
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
425 PM AKDT Thu May 9 2024

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

Areas of low elevation rain/snow and higher elevation snow
continues this afternoon as the second in a series of upper-level
waves and surface troughs moves from north of Kodiak Island
northeast over Southcentral Alaska. The more widespread
precipitation over the Kenai Peninsula this morning has become
more scattered and showery in nature, with snow from Seward to
Kenai this morning beginning to wind down as temperatures warm to
near 40 and the precipitation transitions to rain. Snow showers
have also changed to rain showers across the southern Susitna
Valley this afternoon with the warming temperatures. Elsewhere,
the precipitation is in the form of rain across Prince William
Sound; however, snow continues to fall at higher elevations such
as Thompson Pass where it remains cold enough for the snow to
accumulate on road surfaces.

As the second, weaker trough lifts north this afternoon/evening,
the southeasterly flow aloft will shift south and southwest by
tonight. This shift will reinforce the colder air already in
place aloft, with 850mb (~4,500ft MSL) temperatures falling
another 2 degrees from -5C to -7C. As the flow shifts to the
southwest, the precipitation over Cook Inlet will swing back
toward Anchorage and the Mat-Su Valleys. Like yesterday, the
challenge will be how cold surface temperatures get and how
intense the precipitation to allow snow to reach the surface.
There is high confidence that snow will return to the hillsides
of Anchorage and Eagle River this evening, but lower confidence
for places like the Anchorage Bowl and from Palmer to Talkeetna.
The precipitation will come to an end from west to east beginning
late tonight as the trough departs and a weak, transient ridge
works over the region in advance of the next system. Southerly
winds will again increase this evening as the trough lifts north.
These winds should diminish in intensity overnight.

This ridge will yield drier and perhaps even a bit sunnier
conditions for at least the first half of Friday for some. By
Friday afternoon, a stronger low moving up along the AKPen will
extend its front into the Gulf as strong southeasterly flow
begins to pick up out ahead of this feature. Gusty south to
southeast winds will spread from Kodiak Island back into the
remainder of Southcentral through Saturday as the front slowly
lifts north and the parent low shifts into the western Gulf.
Steady low elevation rain and mountain snow will primarily be
focused along the coast and across Prince William Sound, while
strong cross-barrier flow keeps most of the inland portions of
Southcentral mostly dry. Temperatures will remain cool, but will
begin to rebound closer to seasonal norms in the low 50s over
interior valleys by Saturday afternoon and perhaps a few mid 50s
for Sunday. The front and its parent low slide east on Sunday,
with only a few showers lingering along the coast.

-TM

&&


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

A weakening polar low south of the Aleutians continues to move
east towards the Gulf of Alaska through tonight, providing
some showery activity along the southern Alaska Peninsula coast.
Ridging over Southwest will allow for calmer conditions across the
area tonight into tomorrow morning.

The bigger area of concern is the larger low tracking across the
western Aleutians. Widespread precipitation is likely as the low
and extending occluded front move eastward through Friday
afternoon. Warm air along the front will result in many locations
going above freezing, making most of the precipitation along the
Aleutians rain. Gale force winds will persist into Friday morning,
with localized areas along the Aleutians like Cold Bay getting
wind gusts up to 45 mph. The low will reach Southwest by Friday
morning, producing widespread showers across the area through
Sunday morning and small craft winds along the Bristol Bay and
Kuskokwim Delta coastline through Friday evening.

A new low forms south of Shemya Saturday morning, moving eastward
along the south side of the Aleutians through Sunday afternoon.
Precipitation type could be more of a rain/snow mix as cooler air
is brought in by the low. Winds will not be as significant of an
issue as the previous low, with winds only reaching small craft
force throughout its duration.

-BS

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

A high amplitude, positively tilted trough extends from the
Arctic across Western Alaska into the North Pacific South of the
Aleutians. This trough weakens and become more shallow through the
forecast period. This allows a number of energetic shortwaves to
gain energy from the North Pacific and pass through the nearly
zonal flow for Thursday. New features from Siberia brings some
undefined changes after Wednesday. Model agreement is reasonable
during the first half, but changes to more uncertain conditions
through midweek, especially in the Western half of the forecast
area.

The extended forecast opens somewhat quietly as Gulf low move the
active weather into Southeast Alaska. Locally heavy rain over
Prince William Sound and the Copper River Basin dissipates
Tuesday. A broad surface ridge over the Bering begins to flatten
through Tuesday. Showery precipitation is expected to spread over
the Aleutians, Bering and Alaska Peninsula ahead of the ridge. In
the far West, the first Siberian low brings gusty winds and
precipitation starting as snow, but quickly changing to rain
across the Aleutians and Bering. This low and front pushes some
mixed precipitation into Western Alaska, trailing over the
Aleutians for Tuesday and Wednesday before diminishing over the
AKPEN Thursday. Locally heavy rainfall moves inland over the West
as the low moves into the Lower Yukon Valley through Thursday.


- Kutz

&&

.AVIATION...

PANC...Predominantly MVFR ceilings and visibilities with
intermittent periods of IFR ceilings are expected this afternoon
and evening as another round of mixed rain/snow showers moves over
the terminal. Light northerly winds early this afternoon will
shift back to the southwest around 4pm, then to the southeast by
6pm this evening. Winds may gust to between 25 and 35 mph through
the overnight hours before diminishing early morning Friday. Any
rain/snow showers should also come to an end by late Thursday
night, with conditions improving to VRF, as the precipitation
moves east over the higher terrain.


&&


$$