Small Craft Advisory 1010, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
436 AM AKST Thu Nov 16 2023

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

Key Takeaways:

1) Snow continues for the northern Susitna Valley. Locations
along the Parks Highway between Milepost 120 and 180 may receive
over a foot of additional snowfall. A winter weather advisory
remains in effect through 5PM Friday.

2) Coastal locations along the eastern Chugach such as Cordova
and Valdez should see their heaviest snow thus far this year.
Between 5 and 10 inches likely for these coastal communities.

3) The coldest air of the season so far will arrive on Friday and
persist through the weekend. Expect overnight lows around 0 for
the Anchorage Bowl and much of the Kenai Peninsula, below 0 for
much of the Mat-Su Valley, and below -10 for the Copper River
Basin.

GOES water vapor imagery shows broad upper-level troughing across
much of Mainland Alaska and the Bering Sea, with the primary
longwave axis now along the western AK coast. This places much of
southcentral Alaska in relatively warm and moist southwest flow.
As of 4am, temperatures have warmed into the 30s and 40s across
much of the lower-elevations of the Kenai Peninsula and Anchorage
bowl. The Matanuska and Susitna Valleys remains below freezing, as
well as the Copper River Basin southward to Valdez.

A shortwave trough embedded within the southwest flow has
fostered an increase in rain/snow coverage stretching from the
Cook Inlet northward into the Susitna Valley. With additional
shortwave energy upstream, along with a fairly strong cold front,
precipitation will continue for these areas through much of
Thursday and into Friday. A winter weather advisory continues for
the northern Susitna Valley where up to a foot of additional
snowfall is likely.

The aforementioned cold front will work its way across
southcentral Alaska through the day today, resulting in a
changeover back to snow in any areas receiving rain. Snow will
taper down across the Mat-Su Valley and Kenai Peninsula Thursday
night. Some light snow cannot be ruled out for the Anchorage bowl,
but accumulation will be rather limited. Snow will increase
across the eastern Chugach and Copper River Basin as the cold
front brings cold, moist flow into the coastal mountains.
Locations such as Valdez and Cordova are likely to see their
heaviest snowfall thus far this season. Both locations may pick up
between 5 to 10 inches depending on elevation above sea level.

Precipitation will taper off for the eastern mainland Friday
night. 850mb temps within a couple degrees of -15C underneath a
building ridge will promote cold temperatures, especially
overnight in locations that manage to clear out. As mentioned
above, the coldest temps of the season are expected. Overnight
lows below 0 will occur in many locations such as the Mat-Su
Valley and Copper River Basin. Much of Anchorage will sit within a
couple degrees on either of 0 Fri-Sun nights.

-Brown

&&

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

The strong low that has been the primary weather maker across the
region over the past couple days has now moved inland over
Southwest this morning. This is finally allowing the onslaught of
southwesterly and onshore winds to come to an end as winds become
increasingly northwesterly. Much colder, Arctic air is now
spilling into the Bering Sea and making steady progress into
Southwest as well as it wraps into the base of a deep upper trough
extending from near Norton Sound to the AKPen. The few spots in
Bristol Bay still holding on to rain showers should soon flip over
to snow showers later this morning as gusty winds continue to
advect colder air in from the west.

Overall, little change to the synoptic regime setting up behind
the departing low pressure system is expected for the next day or
two. Widespread ocean effect snow showers already developing in
the central and eastern Bering Sea will continue to impact the
Kuskokwim Delta Coast, AKPen and Aleutians at times through
Friday. Some areas of blowing snow and reduced visibility will be
possible through tonight as squalls of showers move ashore,
particularly on the north side of the AKPen and along the
Kuskokwim Delta near Etolin Strait. Northwest winds in gale force
range near the Southwest coast will slowly diminish through Friday
as well, but will hold on for a while longer where enhanced out
of gaps and passes near and south of the northern AKPen.
Otherwise, the return to colder temperatures will be the main
story, with highs in the 10s to 20s and lows mainly in the single
digs returning to much of Southwest through Saturday. Out across
the Bering Sea and Aleutians, winds will shift from northwest to
westerly as a shortwave trough drifts into place, but wind
intensity should stay at or below small craft range through
Friday.

Looking out ahead toward the tail end of Saturday, a strong front
stemming from a Kamchatka low will approach the western Bering
Sea with rain and strong, southerly flow reaching the western
Aleutian Chain by Saturday night. Early indications are for this
front to arrive in the Bering with winds well into storm force
range. Stay tuned as we monitor this next system into the upcoming
weekend.

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

The long term forecast period begins on Saturday. A cooling trend
will be well underway with temperatures around 10 degrees below
normal. Light to moderate snow should be ongoing across the
Copper River Basin and portions of Prince William Sound, east, as
an upper low shifts into Southeast Alaska into Saturday night. A
cold longwave trough will continue to dig south and east over
mainland Alaska and will bring the coldest air of the season to
southern Alaska with temperatures around 10 degrees colder than
normal into early next week. At the same time a drier air mass
will help to clear out most precipitation for both Southwest and
Southcentral through the weekend. The exception will exist over
the Bering where isolated to scattered snow showers are forecast
with the trough's passage. A Kamchatka low then brings a strong
front into the Bering Sunday into Monday with potential high winds
as the front moves through the Western and Central Aleutians. The
front will progress into the eastern Bering by Monday with a
rain/snow mix and enhanced southerly winds along the front, from
the Eastern Aleutians up into the Chukchi Sea.

CC

&&

.AVIATION...

PANC...Downsloping is expected to keep most of the precipitation
east of the airport today. There is a chance for very light snow
in the morning but no accumulation is expected. Gusty southerly
winds will continue into late tonight, diminishing and switching
to northerly after 12Z Friday morning.

&&