Small Craft Advisory 484, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 AM AKDT Tue May 30 2023

.ANALYSIS AND UPPER LEVELS...
The cool pattern over southern Alaska continues this morning while
an upper level low over the Gulf of Alaska moves north along the
AlCan border and weakens. A portion of the upper level low over
the Bering Strait will break away and descend across Southwest
Alaska to form a new low in the Gulf. The surface ridge along the
north Gulf coast and thermal low inland break down, calming
localized gap winds.

An upper level ridge will build over the Bering and move over
Southwest Alaska Wednesday evening after the runaway low from the
north reaches the Gulf.

&&

.MODEL DISCUSSION...
Models are in reasonable agreement in the synoptic scale features.
As the shortwave moves down from the north, the NAM brings a weak
trough across the Anchorage area Wednesday night roughly six
hours ahead of the GFS, with the others falling within that
range. While the exact timing is not yet settled, confidence
seems high that lingering precipitation and clouds will clear out
following this event.

Out west, models are in good agreement with mid level cold air
dropping down, the only question is how cold and windy it will
get with this low.

&&

.AVIATION...
PANC...VFR condition will persist. A light sea breeze is expected
through this afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Tuesday through Thursday)...

Weak low pressure drifting in the Gulf of Alaska and a transient
easterly waves across the Copper River Delta and Mat Valley are
rounding out the weather picture for Tuesday. Starting out east
in the Copper River, the type of precipitation you will see is
dependent on the elevation travelling this morning. Areas around
Glennallen will see the cool temps and rain continue into the
evening. North near Paxton, and at the higher elevations near
Eureka, snow will mix with the rain as temperatures have dipped at
or below freezing. Daytime "heating" will give a little respite
from the snow/rain but continued light showers are expected again
overnight Tuesday into Wednesday. Across the Anchorage Bowl, some
lingering light showers may remain around the mountains into the
afternoon. Skies will remain mostly cloudy, though a few pokes of
sun could happen into the afternoon hours. Anchorage proper
should remain relatively dry for the day, though light showers
will occasionally develop. The increased cloud cover will keep the
area cooler when compared to Monday's sunny warmth. The normal
high for the end of May is right around 60 degrees. Most
locations will stay 4 to 10 degrees below that.

Wednesday a weak upper level trough of low pressure will move from
Denali, southeast towards Yakutat. Very little precipitation is
expected with this weather feature. Ridging and fair(er) weather
will occur behind the exiting trough and daytime temperatures and
drier weather will again begin to rebound into the latter half of
the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3)...

The pattern continues with a weakening low dropping south across
Southwest Alaska, carrying an unseasonably cold air mass in its
wake. A light rain/snow mix is possible across western Kuskokwim
Delta this morning, with light rain showers expected elsewhere
through today and snow possible along the higher elevations.
Precipitation is expected to diminish later this evening as the
low pushes into the North Pacific and dissipates. Winds will
increase to small craft along the eastern Bering Sea as well as
through the gaps and passes of the Alaska Peninsula with gale
force gusts. High pressure ridging remains in place over other
portions of the Bering Sea through Thursday afternoon ahead of an
approaching Kamchatka Front.

&&

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

Southern mainland Alaska will find itself sandwiched between two
upper-level lows toward the end of the week. One low will attempt
to encroach from the west over the Bering Sea, while the other
will be situated over the southern Gulf of Alaska. This will place
much of the land in the forecast area under a precarious but
slow-moving ridge, reinforced by warm air and a shortwave ridge
extending westward from Canada, which should allow for a series
of warmer, drier days this weekend. Afternoon rain showers will
remain possible, however, with the warmer surface temperatures
and increased instability as a result. Shower activity may also
be aided by any weak easterly waves rotating around the Gulf low
from Canada and Southeast Alaska, for which forecast confidence
is too low to pinpoint presently. This looks to culminate on
Saturday with the warmest temperatures expected across the
southern mainland. Meanwhile, a large upper low will promote
unsettled weather across the Bering Sea and Aleutians through the
weekend, with some potential for a gale force low to affect the
region. While uncertainty increases Sunday, conditions will have a
chance to trend back cooler and wetter for the southern mainland as
the Gulf low begins to lift across Southeast Alaska. The
magnitude and extent of increased precipitation and cooler
temperatures will depend on the evolution of the low, its track,
and any strong shortwaves rotating around it. The greatest
chances for precipitation on Sunday and Monday will occur along
the north Gulf coast and over the Copper River Basin, with lower
chances elsewhere across Southcentral. Out west, there is good
agreement that a Bering low will push a front to the Southwest
coast for Monday, bringing rain and increased southeasterly
winds.

&&

SYNOPSIS AND MODEL DISCUSSION...ER
SOUTHCENTRAL ALASKA...SS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...CQ