Gale Warning 159, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
522 AM AKST Fri Feb 17 2023

.ANALYSIS AND UPPER LEVELS...

A strong southwesterly jet positioned along the central Aleutians
and stretching into the Gulf of Alaska continues to draw southerly
moisture into the region. This jet continues to support a low that
has tracked into Southwest Alaska and is producing widespread snow
across portions of Bristol Bay and the Kuskokwim Delta early this
morning. Strong winds are also being observed in these locations
producing reduced visibilities. On Nighttime microphysics, a
well- defined low is noticed located in a deep trough positioned
over the western Bering Sea and Aleutians and has been nearly
stationary. This set-up will continue to support the development
of lows south of the chain and then pushing them into the AKPen
and the Gulf. A triple point low near Kodiak Island is producing
widespread snowfall across Southcentral this morning. Reduced
visibilities and lower ceilings have been reported in association
with the aforementioned snowfall.

&&

.MODEL DISCUSSION...

Models continue to be in decent agreement with synoptic scale
features, but are still disagreeing with the finer details.
A low pressure system moves out of the northern Pacific tonight
taking a similar track to the last low but a little farther east
and tracking into Bristol Bay on Saturday morning. Models are in
better agreement with this feature compared to previous model
runs. If this track continues, the strongest winds are expected
near King Salmon and south across the AKPen. Another triple low
forms near the Kenai Peninsula along the next front moving into
the Gulf Saturday associated with the parent low across Bristol
Bay. The models are tracking this triple point low near the east
coast of the Kenai Peninsula and up into Prince William Sound,
models are still still trying to iron out how this low will track.

&&

.AVIATION...
PANC...Steady light snow will continue this morning with MVFR to
IFR conditions expected. Snowfall is expected to be around 1 to 2
inches before ending in the afternoon.

&&

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

Southcentral will remain along the northern periphery of the upper
level jet stream, resulting in continue active weather with fast
moving storm systems. A potent short-wave approaching Southcentral
this morning will elongate and split into two waves, one headed
east across the northern Gulf and one lifting northward across
Southcentral. As a result, the heaviest snowfall will be this
morning, primarily from the Kenai Peninsula to the southern
Susitna Valley. With a triple point low tracking south of the
Kenai Peninsula early this morning, strong and gusty easterly flow
across the Kenai and Chugach Mountains will initially limit
snowfall in Anchorage and the Matanuska Valley. However, flow will
quickly weaken and shift around to the west as the low progresses
eastward later this morning. Thus, steady snow will overspread
nearly all of Southcentral by late this morning, then lighten up
this afternoon as the upper level forcing weakens. Meanwhile,
strong cold air advection combined with pressure rises behind the
low will bring strong westerly to Kodiak Island and the Gulf
today. The fast progression means the strong winds will not be
very long-lived in any one location.

There will not be much of a break before the next system moves in
tonight. This will bring rain and snow to Kodiak tonight and
another round of snow to Southcentral Saturday through Saturday
night. There will be a lot of similarities to the current storm
system. The triple point low does look weaker, which would mean
less wind out ahead of it across the Kenai Peninsula/Turnagain
Arm. The upper trough will move through slower, with upslope
snow lingering along the west side of the Chugach and Talkeetna
Mountains through early Sunday morning. Still, overall snow
amounts with this system will be light. This system will help
flatten the upper ridge sitting over the East Pacific/Gulf of
Alaska and shift the upper jet southward. This will at least
temporarily bring an end to the fast moving storm systems, with
dry conditions settling in across the region for Sunday/Sunday
night.

&&

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

A low moving inland to Southwest Alaska from the Eastern Bering
has driven blowing snow overnight into the majority of coastal
Southwest Alaska. Reduced visibilities, particularly in coastal
areas such as Kipnuk down to Platinum are still being observed.
Conditions will continue this morning, however will diminish first
for coastal communities near Bristol Bay in the late morning, and
by noon for communities near the Kuskokwim Delta. Remaining
onshore flow and snowfall associated with the passage of this low
will weaken through today, and is expected to end by early evening
today. The reprieve will be short-lived however as a new low
approaches Saturday morning, with a leading band of precipitation
to enter the Southern Alaska Peninsula around midnight tonight.
Precipitation on the northern side of the Alaska Peninsula, near
Pilot Point and Port Heiden may see periods of mixed precipitation
and rain before returning to snow by Saturday morning.
Precipitation expected for the remainder of coastal Southwest
Alaska is expected to remain snow for the duration of this event,
which is currently expected to persist through Saturday, lingering
longer inland near Aniak and Lime Village. Northern Bristol Bay
area may expect to see around 2-4 inches of additional snowfall
from this Saturday system. Areas further inland, such as near Lime
Village, may see 1-3 inches of additional accumulations.
Following the passage of these systems, a more significant break
in active weather is expected for Southwest, as a mild ridge
begins to develop and steady on-shore flow sets up by Saturday
evening. This break currently appears to persist through the
weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 to 3: Today
through Sunday)...

A low in the southwestern Bering sea pushes an extended trough,
and subsequent low formed at the triple point currently near
Mekoryuk, inland into Southwest and Western Alaska this morning. A
fairly benign pattern across the Chain will soon be disturbed by
the introduction of a new low looking to move into the Eastern
Bering Sea from the North Pacific by late tonight/Saturday
morning. Precipitation along the leading edge of this low will
stretch from the Central Aleutians to the Alaska Peninsula by
early this afternoon. Precipitation associated with this initial
wave is expected to begin as mixed precipitation, with areas of
snow and rain possible through tonight. Precipitation in the form
of snow will reach the Pribilofs by this evening. This front, and
low, will quickly push northeastward into Mainland Alaska by
Saturday morning. Colder air will fill in behind the departure of
this low, allowing for fairly benign weather this weekend, with
the exception of occasional periodic showers for the Aleutians.

&&

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

The long-term features higher confidence that a frontal system
will move through the central Bering Sea/Aleutians during the day
on Monday. This front will eventually move through Southwest and
Southcentral Alaska Monday evening through the day on Tuesday.
There are some model differences in the strength of the front, but
the overall synoptic idea remains consistent.

A broad upper-level ridge in the Bering Sea builds in behind the
frontal system as it progresses eastward to Southeast Alaska and
Canada. This ridge is poised to move over Southwest and
Southcentral Alaska starting on Tuesday and lasting through much
of the long-term into Thursday. While deterministic guidance and
ensemble guidance generally have agreement with the evolution and
progression of this ridge, confidence lacks at this time if there
will or will not be waves of energy traversing around the
periphery of the ridge (a dirty ridge). Thus, confidence is also
low on the tracks/positions of any potential shortwaves traversing
the ridge periphery. Currently The GFS/CAN/ECMWF ensemble suites
as well as the ECMWF deterministic guidance depict more of a clean
ridge with little in the way of shortwaves moving around it. The
GFS/CAN deterministic guidance do advertise more in the way of a
dirty ridge with various weak shortwaves rotating around its
periphery. This will be something to monitor as details become
clearer with time.

Confidence is increasing for a period of quieter weather for
Southcentral Alaska Tuesday through Thursday with the ridge axis
moving overhead. Meanwhile, after a break from active weather late
Monday and through Tuesday, Southwest Alaska re-enters moist
southwesterly upper-flow with precipitation chances returning
Wednesday through the rest of the long-term. The Bering Sea and
Aleutian Chain, particularly the western and central
Bering/Aleutians will continue to remain active through the long-
term with persistent troughing overhead and a number of North
Pacific Lows and fronts lifting northward into the Bering through
the long-term.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 125, 155, 161.
MARINE...Gale Warning: 119-120, 131-138, 150, 155, 160, 165, 170-172,
					   174, 178-180, 352, 411, 414.
		 Storm Warning: 351.
		 Heavy Freezing Spray: 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...NSC
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CL
LONG TERM...DN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
242 PM AKST FRI FEB 17 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0113 PM     SNOW             11 SSE ANCHORAGE        61.07N 149.77W
02/17/2023  M1.8 INCH        ANCHORAGE          AK   TRAINED SPOTTER

            NO LONGER SNOWING.

&&

KO