Small Craft Advisory 17, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKST Thu Jan 5 2023

.ANALYSIS AND UPPER LEVELS...

A longwave trough extends from the Bering to the Gulf of Alaska
and the jet core is well south of the Aleutian chain near 34N
latitude. There are multiple shortwaves embedded within the
pattern. The Kenai and the King Salmon radars have been active
early this morning while the Bethel and Middleton Island radars
remain out of service. On satellite imagery, there is a broad
swath of cold air stratocumulus from the North Pacific into the
Bering with an occluded system over the Western Bering with a
series of vortices along the baroclinic zone.

&&

.MODEL DISCUSSION...

The GFS and NAM initialized well with the QPF fields compared to
radar imagery on the King Salmon and Kenai radars at 6z. Fast
forward, the models continue to struggle with the placement of
the surface lows and the upper level shortwaves. The models are
agreeing on the placement of the jet well south of the Aleutian
chain through Saturday with a sliver of the jet coming over the
Kenai Peninsula and Prince William Sound Saturday afternoon.

&&

.AVIATION...
PANC...There have been some light returns on the Kenai radar early
this morning over portions of Cook Inlet...VCSH added to the TAF.
Expecting VFR conditions and light winds.

&&

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

The last of a seemingly endless train of shortwaves is crossing
the Kenai and CHugach Mountains this morning and heading toward
the northwest. This is the source of the lingering snow showers
over those mountains as well as the Kachemak Bay area. Other areas
around the Cook Inlet and Mat-Su regions continue to downslope
out on the lee side of the mountains as has been the case for the
past few days. With the departure of this final wave, there should
be some clearing and cooling conditions across Southcentral later
today through tomorrow. This will likely bring near or below zero
temperatures to a number of areas tonight and/or Friday night.

The cold temperatures will not be a long cold-snap as the next
system will move toward Southcentral from the Gulf perhaps as
early as Friday night for eastern Prince William Sound and the
eastern half of the Copper River Basin. There is quite a bit of
uncertainty as to the timing and structure of this next system so
forecast confidence in not very high for the westward extent of
precipitation for Saturday and even precipitation type for
Prince William Sound for Saturday. There is a potential for snow
to reach as far west as Anchorage Saturday night, but this is far
from a certain event at this point.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Saturday)...

The active pattern in Southwest Alaska will continue today as
several shortwaves will move through the area bringing showers
tapering off by Friday morning. Steady snowfall along the
northern edge of Bristol Bay will continue through today, tapering
off this evening. These showers are expected to keep mostly in
the Greater Bristol Bay area, and precipitation type associated
with these showers will continue to be snow. Snow accumulations
are expected to hold within 1-3 inches, with the higher amounts in
areas just north of Bristol Bay. Following the passage of these
shortwaves, a respite in active weather is expected to begin
Friday persisting through the late weekend as a weak ridge builds
over Southwest Alaska. Weak offshore flow will also establish
following the passage of the shortwaves today with gusty winds not
currently expected. Fog is still expected to persist around much
of Southwest today, with a pocket near Bethel expected to develop
overnight tonight.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Saturday)...

A large complex of low pressure systems resides across the
Western/Central Aleutians creating widespread windy and showery
conditions. This morning, a trough extending from the Western
Bering to the Central Aleutians near Atka and Nikolski will weaken
and lift northward. Remnants of this wave may bring a quick shot
of showers to the Pribilofs tonight. Following this trough will be
a North Pacific low pressure system approaching the Western
Aleutians this evening. This system will bring widespread Small
Craft Advisory winds with pockets of Gales around the
Western/Central Aleutians into the weekend. Precipitation
associated with this system will begin near Amchitka and spread
across the Western Chain. This system will also be pushing a front
eastward, reaching Atka by Friday afternoon and the Pribs by
Friday night/Saturday morning. As the low approaches the Chain
this evening, precipitation in the Western/Central Aleutians near
Amchitka may see a transition from snow to mixed with rain, back
to snow by Friday morning. This is due to some warmer air
entrained in the core of the system, however as it makes its way
into the Bering, colder air will return shifting the precipitation
back to mixed and/or snow. Snow accumulations across the
Western/Central Aleutians will range from 1-2 inches for today,
and up to 3 inches on Amchitka overnight tonight and Friday.

$$.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

There is not great agreement at the beginning of the week, with a
series of surface lows across the Bering Sea and Gulf of Alaska.
This is fairly common, as model spread tends to grow as they
progress further out in time. There is, however, better than
average agreement for a North Pacific low tracking south of the
Aleutians through mid-week. Discrepancies begin to grow again by
Wednesday afternoon when the GFS and EC continue tracking east
where as the Canadian stalls south of the Eastern Aleutians,
before merging with yet another incoming system from the west.
Active weather is likely along the Aleutians through the long
term.

High pressure sets up over eastern Siberia and across Interior
Alaska. Most of the Mainland will be on the drier side, with
around normal temperatures through mid-week. There is a low moving
into the Gulf of Alaska on Sunday that is going to rapidly
weaken, but there may be periods of snow showers for the Coastal
regions Sunday into Monday morning.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...175 176 177 411 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CL
LONG TERM...KM