Gale Warning 700, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 AM AKST Wed Nov 15 2023

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

Rain and snow continues for much of the southcentral Alaska today
as as a trough digs across western Alaska, with its warm/occluded
front extending well out ahead of the low center. A winter
weather advisory continues for the Susitna Valley, where areas
north of Talkeetna along the Parks Highway are likely to receive 1
to 2 feet of snow, with locally higher amounts. Speaking
probabilistically, current thinking is about a 50% chance of
seeing 3-day snow totals above 8 inches for Talkeetna and about a
70% chance of seeing 3-day snow totals above 18 inches further
north in Chulitna.

Farther south, the 12z AFC sounding shows strong southeast flow
in the low-levels, centered at about 2000ft. This strong southeast
flow will continue to intensify this morning, resulting in quite
the downslope "precipitation hole" across much of the Anchorage
bowl. Additionally, temperatures for Anchorage and the surrounding
lower elevations will warm above freezing today thanks in part to
the downsloping wind. A concern remains for portions of the east
Anchorage Hillside and south Anchorage adjacent to the Turnagain
Arm, where strong winds will continue to gust in excess of 40mph.

In the latest forecast update, have kept precipitation as snow
just a bit longer in places such as Whittier and Portage where
temperatures remain on the colder side. Given upslope flow and
plenty of moisture coming off the coast, a quick few inches is
likely for Whittier this morning before a turnover to rain later
in the day thanks to relatively warm onshore flow. Portage Valley
may hold onto snow a little bit longer, with around a foot of snow
possible. However, temps near freezing and a wet snow or
rain/snow mix may very well compact snow to less than that. This
remains one of the higher uncertainty areas of the forecast and
will continue to be monitored through the day.

The downsloping across the Anchorage Bowl will subside towards
the late afternoon, with models hinting at some light
precipitation filling back in... though warm temperatures creates
a precipitation-type challenge. The hillside and east Anchorage
should return to being cooler than elsewhere in the city. These
places are more favored for some light snow accumulation, with
areas farther west struggling to accumulate much additional snow.
Generally speaking, totals remain on the light side for Anchorage,
Mat-Su Valley, and western Kenai where up to just a couple of
inches are possible. Can't rule out a few flakes towards the
center of the Copper River Basin by Glennallen, but accumulation
looks minor in this area.

The aforementioned upper-level trough slowly crosses southcentral
Alaska Thursday into Friday. Temperatures really begin to drop
through the lower-levels Thursday afternoon, resulting in a
changeover back to snow for anywhere that was previously too warm.
Shortwave troughs and upslope flow will result in some lingering
snowfall, though coverage will gradually diminish through the day.
Friday night will be the coldest night of the season for many
locations across southcentral Alaska as temperatures drop into the
single digits and, in some cases, below 0 for the first time
since last winter/spring.

-Brown

&&

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

A storm force low in the Bering Sea has now past it's peak
intensity, with the central lowest pressure now coming up slightly
to about 965 mb. The center is continuing to make steady progress
east-northeast, now located just northwest of the Pribilofs. The
main corridor of storm force winds is scraping past the central
Aleutians to the north, and is also beginning to nose into waters
near and south of St George Island. The low's occluded front now
bends north and east out to the Norton Sound, and farther out,
south and east into the Lower Kuskokwim Valley and Alaska Range.
Warm air has infiltrated much of Southwest with deep
southwesterlies moving in behind the frontal passage, with most
lower elevations now sitting several degrees above freezing.

Overall, very few changes to the forecast have been made for this
package. The overall thinking for the low moving inland and the
subsequent return of Arctic air and north to northwest flow as
the low and attendant upper trough shift farther east into
Mainland Alaska later in the week. Winds have now peaked in the
past few hours along the central Aleutians, and while a few gusts
in the 60 to 70 mph range will still be possible in Adak and Atka
for the next few hours, an overall downward trend in gusts should
continue throughout the day. As the low and corridor of stronger
winds shift east today, it will also graze the eastern Aleutians,
with a few gusts into Dutch Harbor up to 65 mph possible later
this afternoon.

Looking back towards Southwest, the main concern in the short term
continues to be the strong, onshore winds now picking up near gale
force into the coastline of Bristol Bay and the Kuskokwim Delta.
Coastal Flood Advisories remain in effect for both areas due to
potential surge of 2 to 5 ft above the normal high tide line. The
worst potential for water reaching these levels will be during the
next high tidal cycle this evening along the northern shoreline
of Bristol Bay. The threat for coastal flooding/erosion will end
later tonight as the low moves inland and winds shift from onshore
to northwesterly.

Shifting attention to Thursday and beyond, things will quiet down
quite a bit but also become much cooler as Arctic air spills
south and east in the wake of the departing low. Rain showers over
Southwest will turn to snow showers over Southwest, then mostly
shut off away from the mountains between Thursday and Friday as
the low levels dry out. Numerous ocean effect snow showers will
also develop across the Bering Sea as Arctic air moves over a
still seasonably warm sea surface. These will intermittently
impact most of the Aleutian Chain, AKPen, and along the Kuskokwim
Delta Coast near Etolin Strait between Thursday and Friday as
below average temperatures also settle into place.

&&

.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...Cloud ceilings are expected to drop below 5000' this
morning and dropping below 3000' by this afternoon. Periods of
IFR conditions are possible overnight. Southerly winds will pick
up later this morning, gusting to 20-25kts at times, and should
diminish again later tonight. Chances for snow linger throughout
the day but it will be light and intermittent. No accumulation
expected.

KM

&&