Gale Warning 557, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
522 PM AKDT Tue Oct 3 2023

.ANALYSIS AND UPPER LEVELS...

One shortwave moving over the PWS area has moved east, as another
shortwave moves southeast across the interior, just brushing the
northern portion of the forecast area where light rain showers
have been noted in the Bethel area. A ridge of high pressure
stretched north across the central Aleutians and eastern Bering.
Farther west, a front is pushing north across the western Aleutian
Islands, bringing widespread rain, gusty winds, and waves to 20 ft.

&&

.MODEL DISCUSSION...

Models continue in fairly good agreement on the overall synoptic
pattern. The shortwave over the interior will continue on it's
southeastward trajectory. A low pressure system moving north
toward the eastern Aleutians and the low moving toward the western
Bering is progged to reorient the high pressure ridge to align
west-east across west-central AK by Thursday morning. Medium
range models show the center of the western low roughly over the
far western Aleutian islands with the other just south of Unimak
Island. East of this low, strong southerly winds will usher in a
deep layer of relatively warm, moist air from the eastern
Aleutians eastward across the Gulf, that could persist through
Friday.

&&

.AVIATION...
PANC...VFR conditions will persist Tuesday and most of the day
Wednesday before clouds roll in at the tail end of the TAF period
as precip approaches from the south. Winds will remain light
northerly.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Thursday night)...

Using latest satellite imagery, clear skies are found over
southcentral Alaska this afternoon. But looking farther south, the
next weather maker can be found.

An area of low pressure will track northward towards southwest
Alaska and the Aleutians. A front associated with the low will
swing towards the southern coast, should reach the coast Wednesday
night. Along the front will be elevated wind speeds, upwards of 25
to 40 kts for marine areas, land areas will see sustained wind
speeds around 10 to 20 mph. Higher wind gusts likely.

This front will also bring precip. While rain is mostly expected,
some snow is possible before the warmer air arrives. Confidence
is high that coastal locations will see rain with this event.
However, there should be enough cold air in place across the
Copper River Basin for at least a couple of inches of snow before
the snow mixes with or changes over to rain Thursday afternoon. A
similar scenario is also possible for the Susitna Valley; however,
there is a higher level of uncertainty as to how much cold air
will be in place at the start of the event. Currently, it looks
like areas around Willow and Skwentna could see some snow before a
changeover to rain.

&&

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

Predominately dry and cool conditions, with nighttime lows around
freezing for the near-term across the Southwest - the first prominent
bout of colder temperatures into Southwest this Fall. Elsewhere
along the Aleutians, overnight temperatures in the 40s will
prevail. The focus of this discussion will be on the two low
pressure systems affecting the west. The first is currently moving
from west to east bringing light to moderate rainfall and gusty
winds (up to gale-force) over a vast swath of the western
Aleutians and surrounding marine areas. This system will slow and
fizzle by Wednesday morning as the low to the south of the eastern
Aleutians and western AKPen continues to propagate northward.
This system will bring widespread gusty gale-force winds (as far
north as Bristol Bay) and mixed precipitation to the region,
spreading northward across the southwest where cold air is already
in place. Light snow is forecast for interior locations, rain to
coastal areas, and a rain-snow mix is forecast for the area in
between beginning as early as Wednesday night as the system
progresses north. There is a period where freezing rain may be
noted across areas of the Lower Kuskokwim early Thursday through
the afternoon. For now, while confidence in low in this occurring
(3-8% chance of occurrence), have chosen to not add this into the
forecast, but will have to continue to monitor as the forecast
evolves.

Upper level support for this system transitions east Thursday
night and early Friday, with the low quickly losing strength over
the period. Should see it drop south of the AKPen as it fizzles
into the weekend.

Lastly, Shishaldin is still lofting ash, as detected on satellite
imagery. Areas south and west could see trace amounts of ash under
the current pattern. Please see the current Special Weather
Statement for further information.

&&

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

A well developed upper level longwave trough extends across the
Bering into the Gulf of Alaska through Tuesday. Several model
defined embedded surface low centers will transit through and
around the trough on various tracks, bringing unsettled weather
across the region. This pattern is expected to continue through
the end of the forecast period.

Saturday opens with a low centered over the Alaska Peninsula, and
is accompanied by a front spreading precipitation across much of
southern mainland Alaska. Rainfall will be heaviest along the
Eastern Kenai Peninsula Coast all the way over to the Copper River
Delta and Canadian Border with lesser amounts, but possibly mixed
rain and snow inland, and tapering off through Tuesday.

Northeasterly winds drawn from Interior Alaska through the
Kuskokwim Delta will result in gusty offshore winds increasing to
near gale force for Kuskokwim Bay and parts of Bristol Bay and gap
winds off the Alaska Peninsula and Barren Islands for Sunday into
Tuesday. Gusty winds across the Pribilofs to the Aleutians Sunday
through Tuesday. A weak ridge over the Western Bering yields to a
North Pacific low center moving along the Pacific side of the
Western Aleutians for the end of the period.

&&

SYNOPSIS AND MODEL DISCUSSION...NR
SOUTHCENTRAL ALASKA...GS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AB
LONG TERM...MK