Small Craft Advisory 79, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKST Tue Jan 24 2023

.ANALYSIS AND UPPER LEVELS...

Moisture stretching from deep in the tropics will work its way
into the coastal region today and tonight. A developing surface
low south of Cold Bay will tap into this moisture as it continues
to drive north to the Gulf of Alaska. Showers linger as an
occluded front drapes east from the AKPEN to Canada. Temperatures
remain above freezing south and east of Willow, aided by moist
and warm southwesterly winds. Freezing levels hover between 1500
to 2000 ft this afternoon, meaning that most precipitation falling
will come down as rain.

&&

.MODEL DISCUSSION...
Model guidance has improved over past days/runs. Over the last
few days, models have struggled with the evolution of a surface
low parked over Dutch. As of this morning, all global models
(global and hires) have all come into agreement with the
development of the aforementioned low moving northeast, sliding by
Kodiak and arriving in Prince William Sound tomorrow. This
afternoon, the GFS is the only outlier, but is only lagging by 6-8
hours behind all other models. All guidance agrees on cold air
filling in as this low lifts north, bringing temperatures across
the region back below freezing.

&&

.AVIATION...

PANC...VFR conditions will persist. SE wind gusts will begin to
abate late this afternoon as the Turnagain Winds weaken.
Precipitation is expected late tonight and into tomorrow morning.
Precipitation type questions still exist due to the forecast
cooling and lingering warm (present) surface temperature. Ceilings
will fall but remain vfr during the precip time frame.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Friday)...

Unsettled weather continues across Southcentral as various upper-
level shortwaves lift north across the region and a surface front
weakens along the north Gulf coast. This afternoon, scattered
showers linger along the coast and slightly inland in the form of
light rain or a wintry mix. In the Susitna valley, precipitation
transitions to snow roughly to the north and west of Talkeetna,
with only a few more inches likely for this evening before
precipitation tapers off there.

Precipitation along the Southcentral coast continues tonight and
into Wednesday as a Gulf low extends its front to the north Gulf
coast. The heavier precipitation with the front is expected to
arrive early Wednesday morning as the low center follows in tow,
tracking eastward towards Cordova by the afternoon. Because models
are continually favoring a more eastward track of this system,
there is increasing confidence that the bulk of precipitation will
be focused over Prince William Sound (as rain) and the Copper
River Basin (as rain or freezing rain) tomorrow. Precipitation
north of Glennallen and up to the Alaska Range is expected to fall
mainly as snow. The Anchorage Bowl and Western Kenai Peninsula
will likely be right on the western edge of this system and should
see much drier conditions, however scattered showers are not out
of the question. If light precipitation does fall tomorrow, it
should start as snow early in the morning before temperatures
slightly warm during the day, promoting a wintry mix or rain.
Nonetheless, with the more easterly low track, much lighter
precipitation is expected for Anchorage and Western Kenai
Peninsula than was anticipated a few days ago.

By tomorrow afternoon, precipitation starts to lighten over
Prince William Sound and the Copper River Basin as the low
weakens. The front lingers along the northeastern Gulf coast on
Thursday while an upper ridge approaches from the Gulf of Alaska.
Clear and dry conditions, and a return to cooler temperatures,
unfold across Southcentral for Friday as the ridge continues to
build overhead.

&&

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

A southwest-to-northeast oriented warm front is pushing northward
into the Bristol Bay region this evening and will warm up
the area near the Aleutian Range as easterly winds with warm air
spill in from the Gulf side. This will bring in the possibility
for rain to mix in this evening from Iliamna southward. Areas
west of King Salmon will remain west of the frontal boundary and
in the cold air resulting in all snow. The heavier snow will occur
in the Kuskokwim Delta again as the strongest gradient will
increase the lift there overnight and another 3 to 5 inches is
possible across the Delta with 1 to 2 in the Kuskokwim Valley
which will remain in the cold air as well. The winds over the
Kuskokwim Delta will diminish some by late evening, but blowing
snow is still likely across the region, but not nearly as bad as
what occurred Sunday into Monday. This snow will end Wednesday
morning as a cold front moves through and brings some reinforcing
cold air back to Bristol Bay. For all of Southwest Alaska, the
story for Thursday into Friday will be a rapid warming trend as
the next front moves in from the southwest and brings in a much
warmer airmass. There is still an unusual amount of uncertainty as
to whether there will be precipitation over the region in the
Thursday through Friday night timeframe. What can be said is that
precipitation that does occur will likely start out as snow but
may tilt toward more to rain or freezing rain by Friday,
especially for areas closer to the coast.

&&

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

A low near Dutch Harbor extends a strong front to the north and
into Southwest mainland Alaska this afternoon. there is a sharp
temperature gradient along this front resulting in the snow and
blowing snow conditions in the Pribilof Islands and rain from
Dutch Harbor eastward for those areas getting precipitation. To
the west of this low there is cold advection off the Bering Sea
bringing areas of snow showers. As this low near Dutch Harbor
swings eastward tomorrow, the next low and front will be rapidly
moving form the North Pacific into the Southwest Bering Sea. At
he same time, an upper level ridge will be building over the Gulf
of Alaska ushering in strong southerly flow aloft for most of the
Bering Sea by Thursday so most of the precipitation for the
Aleutians will be rain. However, by Friday, colder air wraps back
into the region from the Southwest and will result in a rain and
snow shower mix for much of the eastern Bering Sea. By Thursday
night and then into Friday sufficient cold air will be over the
central and western Bering Sea for snow showers as the large,
complex, low sits in the Western half of the Bering Sea.

&&

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

An amplified pattern at the start of the weekend holds until the
the early workweek, when model discrepancies arise as the pattern
progresses. Model confidence regarding the synoptic flow for this
period is strong with lower confidence regarding timing and
intensity of upcoming trough passages. Saturday morning a ridge
will have built over the Gulf of Alaska maintaining an inactive
pattern through most of the weekend in Southcentral. Conversely,
in the Bering multiple troughs aim to make their way through the
Aleutians and Southwest Alaska. The first of which is a trough
that will have already made it to the Eastern Aleutians by
Saturday morning. The progression of this trough however shows
good model agreement that it will be blocked by the ridge out
East, will weaken, and ride the ridge up into Central Alaska by
Saturday late Saturday afternoon. Another 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.

At this point the deterministic model solutions begin to
diverge. The 12Z GFS suggests a slower breakdown of the ridge,
holding off the northward progression of the North Pacific low and
stalling the front that was moving across the Aleutians at the
Central Aleutians and lose its structural integrity by Tuesday
morning. The 12Z Euro solution 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. These very different solutions balance
on a repetitious question for models, how resilient is the ridge?
Typically we see the breakdown of a ridge we err on the side of a
slower breakdown. 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: 141 145.
MARINE...STORM WARNING: 178 411.
         GALE WARNING: 119 170 172-177 351 352 412-414.
         HEAVY FREEZING SPRAY WARNING 179 180 185 412 414:
FIRE WEATHER...NONE.

&&

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