Small Craft Advisory 965, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKST Sun Dec 4 2022

.ANALYSIS AND UPPER LEVELS...

The jet stream runs near the western and central Aleutians and
dips well south before returning north across the AKPen and
western Alaska. The jet max is supporting a shortwave moving
across the AKPen and into the Kuskokwim Delta. A frontal system is
also moving across the Bering towards the Pribilofs just to the
west of the aforementioned shortwave. Ahead of these two system
strong winds are occurring from the AKPen north into Bristol Bay
and the Kuskokwim Delta. The strongest winds are near the coast
and AKPen where 35 to 55 knots have been observed. Farther inland
across southwest Alaska winds are not quite as strong ranging
from 15 to 35 knots. Rain is occurring ahead of the front across
the Pribilofs, AKPen, and the Kuskokwim Delta with temperatures in
the upper 30s to near 40. Farther west another frontal system is
moving into the western Aleutians and western Bering Sea with 40
to 50 knot winds reported at Shemya.

To the east the ridge sits over Southcentral Alaska with mid and
high clouds spilling over the ridge as weak shortwaves move over
the top of the ridge. Otherwise, areas of low stratus have been
observed from Kodiak Island, Cook Inlet and north into Anchorage
and parts of the Mat-Su valleys. Temperatures are a bit warmer
today with 30s and 40s along coastal areas of Southcentral with
mainly teens and 20s inland with the exception of the Copper
River basin with single digits being reported.

&&

.MODEL DISCUSSION...

Guidance remains in good overall synoptic agreement through
Monday. However, models continue to struggle with the progression
of a triple point low that forms along the front near the Kenai
Peninsula and moving across the Gulf Tuesday. The main forecast
challenge in the short- term will be determining the location of
snow and snow amounts with the second system on Tuesday across
Southcentral.

&&

.AVIATION...
PANC...Light winds persist for this TAF package. Ceilings will
primarily begin VFR with periods of MVFR ceilings possible this
evening through the overnight hours. A frontal system will bring
light snow tomorrow morning near 9 AM or shortly thereafter. The
snow will produce IFR ceilings and visibility. 1 to 2 inches of
snowfall is expected near the terminal through Monday evening when
snow is expected to end.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Sunday through Tuesday night)...

The upper level ridge that has been the dominant feature over
Southcentral since mid-week last week will retreat to the
south and east as a series of systems move through. The first
system will move in tomorrow in the form of a weak, north-south
oriented upper level front with a surface low spinning up south of
the Kenai Peninsula and moving into the Prince William Sound.
Precipitation, mostly in the form of snow, will move from
southwest to northeast starting Monday morning over the southern
Kenai Peninsula and Susitna Valley, around noon for Anchorage and
the Mat Valley, and overnight for the eastern Prince William
Sound and portions of the Copper River Basin. Given the dry
airmass in place, it may take some time for the column to saturate
down, so a few hours of virga are likely before the onset of
snow. This system will bring a broad 1-3 inches for most areas at
sea level with 3 to 5 inches over higher terrain of the Chugach
Front Range, Talkeetna Mountains, northern Susitna and Valdez
areas.

While the aforementioned high is considerably weakened, there
will remain a narrow ridge with it's axis extending from along the
AlCan Border south into Southeast Alaska and British Columbia. As
a result, the strong jet and associated upper level lows and
shortwaves will take on a negative tilt as they interact and
deflect south with the ridge. Models are struggling to resolve the
interactions of the shortwaves and attendant, developing gulf
low/lows as they move into the Western Gulf Tuesday morning.
Generally speaking, snow is expected to be widespread, but light
and intermittent for most areas Tuesday and into Wednesday
morning. On Wednesday the low will depart into the eastern Gulf,
which may linger some snow over western facing slopes through the
day. The other story to the low departing will be the return of
gusty winds through outflow areas.

&&

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

An upper-level trough and surface front track east across
Southwest Alaska through tomorrow morning. Deep southerly flow
with the system advects warmer air across the region, keeping rain
as the main precipitation type. These strong southerly winds are
also expected to bring elevated water levels with the potential of
water pushing up through cracks in the ice and ice pushing up
onshore. Thus, a Coastal Flood Advisory remains in effect for
northern Bristol Bay and Kuskokwim Delta coast locations. By
tonight, winds decrease and shift westerly while the front moves
inland and weakens. There will be a respite from precipitation on
Monday before another system approaches from the west. A front
will bring precipitation and increased southerly winds to the
Southwest coast again by Monday evening. By this time,
temperatures are expected to be cold enough to keep precipitation
inland as snow and a wintry mix along the coast. Going into
Tuesday, winds diminish and precipitation tapers off as the front
moves inland and weakens. Various upper-level shortwaves may
promote light snowfall up in the mountains for Wednesday,
otherwise much of Southwest Alaska can expect clearing, colder,
and relatively drier conditions for the end of the short term
forecast.

&&

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

Active weather continues for the Bering Sea and Aleutians as two
main systems transit the region. An upper-level trough and surface
front are currently exiting the eastern Bering and Aleutians into
Southwest Alaska. Gale-force winds and rain will accompany this
front through tonight, after which time the front begins to weaken
over land. A transient ridge builds over the central Bering in
the wake of this first front and ahead of the next system. Another
strong front currently located over the western Bering and
Aleutians will continue producing mainly rain and strong southerly
winds, which are expected to increase to storm- force by this
evening across the western/central Aleutians. Precipitation and
strong winds will spread east across the entire Bering Sea and
Aleutians before reaching Southwest Alaska by Monday evening.
Widespread precipitation and colder air will fill in behind this
front and blanket the Bering/Aleutians Tuesday into Wednesday. By
Wednesday morning, a North Pacific low is advertised to approach
the western Aleutians. Models are currently struggling with the
track of this system.

&&

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

While an active pattern is expected for the latter half of the
upcoming week, strong model discrepancies persist with the
motions and intensities of many of the disturbances. Friday
morning, a shortwave providing some precipitation to Southcentral
will have moved out to the East. A low pressure system in the
Central Bering Friday morning will sweep across the eastern
Aleutians and push into the Gulf by Friday afternoon. The northern
extent of this low, with the EC model bringing a shot of
precipitation to all of Southcentral throughout the rest of the
day Friday and into Saturday morning, whereas the GFS keeps all of
Southcentral dry and the low track through the Southern Gulf. A
similar story is echoed in Southwest Alaska, when the low crosses
the Alaska Peninsula Friday morning, the EC brings a swath of
precipitation across all of Southwest Alaska, whereas the GFS
keeps Southwest dry. Following this low track, GFS begins to build
a ridge over the Southern mainland, where the EC keeps a low
pressure disturbed pattern with widespread light precipitation
lasting through Sunday afternoon. Lastly, the GFS brings North
Pacific low into the Western Aleutians and Bering by Saturday
afternoon. This system will bring widespread precipitation and
sweeps a front across the Aleutians, reaching Southwest Alaska by
Sunday afternoon. The EC has this low just entering the western
Aleutians and Bering by Sunday afternoon. Forecast confidence for
this period begins weak and deteriorates further towards the end
of the workweek.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Coastal Flood Advisory 155 161.
MARINE...Gale 155 165 170 172 174 178-185.
		 Storm 173 175 176 177
FIRE WEATHER...NONE.

&&

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