Brisk Wind Advisory 8, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 AM AKST Thu Jan 26 2023

.ANALYSIS AND UPPER LEVELS...

A longwave trough is centered over the Kamchatka Peninsula/far
western Bering Sea, with a broad ridge over the Northeast
Pacific. The longwave trough is accompanied by a complex low
spinning near Kamchatka as it pushes a well-defined gale-force
front into the central/eastern Aleutians, bringing heavy rain
along with it. Ahead of the front, warm, southerly flow is aiding
the development of a North Pacific ridge, which is beginning to
build across the eastern Bering Sea. A closed upper-level low
centered over the Bering Strait has begun to lift and elongate in
response to the ridge building to its south. This low has been
drawing up widespread stratus from the Bering Sea into parts of
Southwest Alaska, in particular the Kuskokwim Delta, with some
weak onshore surface flow developing. The low is also pushing a
cold front east across the mainland, cooling many locations in
Bristol Bay and the Lower Kuskokwim Valley 20 to 30 degrees since
last evening. With the front pushing east, dry conditions now
prevail across Southwest Alaska.

Temperatures are significantly warmer to the east of the front,
out from under the cold-core upper low and where low-level
southerly flow is more dominant. Conditions are widely above
freezing across Southcentral, in the mid-30s up to near 40 degrees
along Cook Inlet and the north Gulf coast. The Copper River Basin
is one exception to this, with many locations there hovering
around 30 degrees. A few passing shortwave disturbances have
brought light rain showers (and snow showers at higher elevations
above 1000 to 2000 ft) to Anchorage and the Mat-Su Valleys,
dropping a few hundredths of an inch of precipitation through the
overnight hours, though these have largely begun to clear out.
Within the Gulf of Alaska, southwesterly flow is pushing more
widespread showers along the coast.

&&

.MODEL DISCUSSION...

Models are in good synoptic agreement through the short-term
forecast period. There continues to be good agreement that
Southcentral will be primarily dry as a ridge builds up from the
North Pacific. The main forecast uncertainties are in Southwest
Alaska beginning on Friday where the infusion of warm air above
the surface will bring in the potential for freezing rain across
much of the Southwest. While there is increasing agreement
on the precipitation coverage area, uncertainty remains with
precipitation type for the Kuskokwim Delta. Most of the global
model guidance suggests precipitation will remain primarily snow
on Friday, with colder air aloft, while the NAM has a stronger
push of warm air leading to a quick transition to freezing rain
and then rain by Friday evening. For Bristol Bay, there is high
confidence that warm air aloft will lead to a period of freezing
rain. By Friday night, model guidance begins to differ in how
quickly precipitation clears out for the Kuskokwim Delta, with
some models ending precipitation on Friday night, while others
suggest that it lingers through Saturday depending on the location
of and amount of precipitation associated with a wavering front.

&&

.AVIATION...

PANC...VFR conditions are expected to persist, with ceilings above
5000 ft. A stray shower or two may be possible in the vicinity of
the terminal through the morning hours before clearing out. Southerly
winds will gust infrequently to around 20 kt this morning before
diminishing this afternoon. For Friday morning, there is a slight
possibility of fog or low stratus developing in Cook Inlet and
affecting the terminal, though it is generally not favored.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...

A couple weak upper level short-waves overhead of Southcentral
early this morning will quickly exit off to the north and east
today. Low level instability combined with weak cold air advection
and southwesterly upslope flow will cause showers to linger along
the west sides of mountain ranges into the afternoon hours,
particularly the Talkeetna Mountains and the Chugach Mountains
near Cordova/Valdez. Some light snow accumulation is likely this
morning in the eastern Susitna Valley east of the Parks Highway,
while the airmass remains warm enough in Valdez and Cordova for
rain.

A strong upper level ridge will build over Southcentral tonight
through Friday and persist through the weekend, leading to
generally quieter weather across the region. As the ridge first
arrives this evening, winds will become light. Under partly
cloudy to mostly clear skies this will allow temperatures to
quickly drop down below freezing, causing any water left on area
roadways to refreeze.

Warm air will surge up the west side of the upper level ridge on
Friday, first bringing warmer air and some light rain to Kodiak
Island. The warm air will then round the top of the ridge and
move across Southcentral Friday night through Saturday, riding up
and over top of the cold surface air in place. This will result in
strong temperature inversions, as temperatures in the mountains
rise above freezing. Weak vertical motion generated from the
overrunning may produce some patchy light precipitation (possibly
in the form of rain), most likely in the mountains. Temperatures
at sea level will largely remain below freezing, but warmer than
normal for this time of year.

The temperature inversions will introduce the potential for fog
to form. Mostly clear skies seem favorable tonight, but the
temperature inversion will just be beginning to form. By Friday
night when the inversion strengthens significantly, clouds will
be on the increase. Thus, expect any fog that does form to be
localized and short-lived.

&&

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

An swath of warmer air encroaches upon the Southwest coast Friday
morning following a Kamchatka front. Temperatures will steadily
rise to or above freezing, beginning along the coast and then
pushing inland Friday and Saturday. The front occludes and breaks
down as it reaches Southwest Alaska, but there is expected to be
enough of a push of moisture onshore for precipitation to occur,
mainly across Bristol Bay and the Kuskokwim Delta. Delving
deeper, the area from Dillingham to Bethel is likely to see
periods of freezing rain or a freezing rain/snow mix. There is
relatively good agreement for Dillingham to Cape Newenham to see
freezing rain beginning early Friday afternoon. Dillingham will
hold on to the freezing rain into the evening hours while areas
further west transition to rain later in the afternoon. Further
inland to Koliganek will transition to freezing rain later in the
afternoon and persist into the overnight hours and take a more
gradual switch to rain. The eastern half of Bristol Bay and down
along the Alaska Peninsula will be mostly rain with a very brief
period of freezing rain possible in the afternoon. The Kuskokwim
Delta has poorer agreement for how far north and inland the warm
air travels on Friday/Friday night. So there is lower confidence
as to whether there will be full blown freezing rain or if it will
be mixed with mostly snow, namely near Bethel and areas north.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A Kamchatka front is pushing towards the Southwest coast. There
is a band of precipitation and gale force winds stretching south
to north across the Bering Sea. The Pribilof Islands will continue
to see areas of blowing snow into the early morning hours before
switching to rain later in the morning. The rest of the Aleutian
Chain and Southern Alaska Peninsula should see mainly rain. The
front is weakening as it tracks eastward, and precipitation
chances will diminish Friday night.

&&

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

An amplified pattern persists through the weekend and into the
beginning of the workweek. Model confidence regarding the synoptic
flow for this period is high with lower confidence regarding
timing and intensity of upcoming trough passages. A strong ridge
over the Mainland will aide in keeping sensible weather relatively
low impacts for the majority of southern Alaska, with the
exception of the Aleutians. A front will enter the western
Aleutians Saturday afternoon and advance eastward, reaching Atka
by Sunday afternoon. The northern edge of a weak North Pacific low
looks to supplement the disturbed pattern across the central and
eastern Aleutians for the remainder of the weekend. Abnormally
higher temperatures, due to the ridge overhead, will persist
through the weekend with cooler temperatures looking to work their
way back in early in the workweek. The GFS continues to suggest a
slower breakdown of the ridge which will aide in holding off the
northward progression of the North Pacific low and stalling the
aforementioned front to lose its structural integrity by Tuesday
morning. The Euro breaks down the ridge much faster which allows
for the progression of the front moving eastward across the Chain
to merge with the northward pushing North Pacific low, creating a
widespread precipitation event across Southern Alaska Tuesday
afternoon. The main focus will be on when the ridge truly begins
to breakdown to know for sure what kind of sensible weather to
expect for the region. Typically, a strong ridge like the one that
will set up over the region, takes longer to breakdown than what
the Euro is suggesting. However, details will become more clear
with later model runs. Stay tuned to our latest forecast to obtain
the most up-to-date expectations.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 161 195.
MARINE...Gale Warning 165 170 172-174 177-181 185 411-414.
		 Heavy Freezing Spray Warning 180 185 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CQ
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...NS