Small Craft Advisory 960, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 AM AKDT Thu Nov 2 2023

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

A series of low level, inverted troughs and weak upper level
shortwaves will move over Southcentral over the next 36 hours.
These weak perturbations will lead to light rain along the Gulf
Coast today and eventually spreading over into Anchorage and the
Mat-Su Friday morning. Given a stout inversion overhead, there is
likely going to be pockets of light freezing rain for Anchorage,
and the southern Mat-Su along the Parks Highway between Houston
and the Talkeetna Cutoff. The greatest uncertainty is in regards
to surface temperatures and whether or not the rain will be true
meteorological freezing rain or rain falling onto the frozen
ground. This will dictate the extent and/or severity of freezing
rain in whether or not it will just affect roadways or if it will
also freeze to trees, power lines, etc. The most likely area for
true meteorological freezing rain (rain falling into air
temperatures below freezing) is from Willow north to the Talkeetna
Cutoff, where cold air in the valley areas is more likely due to
drainage off of the southwestern Talkeetnas. The reason for the
uncertainty is cloudcover. Air temperatures may not be able to
fall below freezing after warming today to do lack of radiative
cooling over night. Additionally, temperatures have been warmer
the past 3 days, but given that rain easily froze to roadways at
above freezing temperatures last Sunday, there will likely be some
ice in the early morning hours on Friday due to the frozen ground.
Temperatures will warm through the day, which should help to
mitigate the impacts from freezing rain.

Weather on Saturday will remain somewhat unsettled as troughing
amplifies to the west. Generally southerly flow with low level
easterlies through the Gulf will keep light, but steady
precipitation for the northern parts of the Susitna Valley as well
as the eastern Kenai Peninsula. Some solutions have more
continuous precipitation from Anchorage north to Wasilla, but
these are being discounted for now as they are breaking down the
ridge over the AlCan border too quick.

Weather on Sunday will mark a stark pattern change towards colder,
and likely snowier weather for much of Southcentral. A stout
cold airmass and upper level trough will move in from the west.
Temperatures aloft will cool rather quickly, transitioning rain to
snow from southwest to northeast as it moves up Cook Inlet and
into the Mat-Su. Uncertainties associated with snow amounts will
be related to how fast the cold air will move in, which is a
challenge when it needs to go through the Alaska and Aleutian
Ranges. For snow lovers out there, the fact that the cold air will
move through areas like the Kamishak Gap and from the southwest,
looks to be more favorable rather than it having to move through
the dense Alaska Range. A couple inches at sea level look likely
for many of the Cook Inlet areas and Mat-Su right now. Stay tuned.

-CJ

&&

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

Prior concerns about freezing rain for Southwest Alaska,
especially across the Kuskokwim Delta, are diminishing. Models
have trended down precipitation through Friday. This is largely a
result of a Central Aleutian low making further southward
progress, and a front, associated with a secondary low to the
south of the Alaska Peninsula, not making as much of a northward
push into interior Alaska. Temperatures this morning across most
of Southwest remain above freezing. There are exceptions to be
sure. Sparrevohn is sitting right at 32 degrees and Bethel is just
above freezing at 33 degrees. The bigger picture, however, is
that precipitation should fall entirely as all rain or as a
rain/snow mix, instead of a snow/freezing rain mix. A dry air mass
currently over Bethel is slowly moistening up, as precipitation
tries to move into the Kuskokwim Delta from the east. Light snow
is forecast during the morning hours, but accumulations will be
negligible.

The next big weather feature will be an upper trough digging
southward out of the Chukchi Sea and into the Kuskokwim Mountains
Friday into Saturday. Strong northerly flow is forecast to develop
behind the low, which will allow much cooler temperatures to
infiltrate the Bering Sea and Southwest Alaska by Saturday
morning. Scattered snow showers will be possible over the Greater
Bristol Bay area and the Lower Kuskokwim Valley, as an upper
trough becomes stationary over interior Alaska through the
weekend. It has been an unusually warm and drier start to the
winter season this year, but cooler temperatures and the chance
for snow return in earnest over the weekend.

Finally, the Bering Sea can expect to see predominantly east to
northeasterly winds transition to a northerly direction through
late Friday. Small craft winds with gusts to gale force will be
commonplace through the Eastern Aleutians and Alaska Peninsula by
early Saturday.

-BL

&&

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

Reasonably good agreement with the forecast models through the
period, even with the consistently aggressive ECMWF outlier over
the Eastern portions. Weak ridging moves into Northern Alaska, and
a couple of high pressure areas run West to East to the South of
the Aleutians, allowing a series of low centers to drive from the
Russian Far East across the Bering to the Alaska Peninsula. Wet
and windy conditions spread across the Bering into Southwest
Alaska, with a slightly lesser period of active weather over the
Western Bering for Tuesday. Gap winds to gale force expected
through the Eastern Aleutians and Alaska Peninsula Wednesday.

Closing out the weekend in the East is a well developed low near
Queen Victoria Island. Its front extends into Southeastern Alaska
and will swing East to West across the Gulf through Monday. Gap
winds are expected through the Barren Islands and Sitkinak areas,
along with some locally heavy rain along the Southcentral Coast.
Another well developed low swings from the Alaska Peninsula into
the Southcentral Gulf for Wednesday, and repeats the weather
pattern through the end of the week.

-KZ

&&

.AVIATION...

PANC...VFR ceilings along with light northerly winds will persist
through today. A North Pacific low will lift northward through the
Gulf of Alaska through the day on Friday. Light rain looks to
overspread the terminal late tonight or very early Friday morning.
There is a slight risk that some of the rain, at the onset of
precipitation, could freeze to below freezing surfaces even though
air temperatures might be slightly above freezing. The vast
majority of precipitation should be mostly in the form of rain
though. For now, keeping ceilings VFR due to the southeasterly
flow at cloud level. Although while maintaining VFR, ceilings will
likely drop below 5,000 feet late tonight and especially Friday
morning.

-DAN

&&