Gale Warning 776, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
539 AM AKST Sun Dec 11 2022

.ANALYSIS AND UPPER LEVELS...

The pattern remains highly amplified across the Gulf Of Alaska and North
Pacific. On satellite imagery (CIMSS MIMIC PW) there is a fetch of
modified tropical moisture that is 300 miles wide and extends over
2,000 miles south into the Central Pacific which is impressive.
This deep fetch of moisture is entrained into the new low that
will be entering the Gulf Of Alaska today. The jet is north of the
Alaska Range with a jet core of 150 knots. Early this morning the
radars at Kenai and King Salmon have been active. Additionally on
satellite imagery there is the remnants of an occluded front over
the eastern Bering and a new low near Attu Island.

&&

.MODEL DISCUSSION...

The models are in decent synoptic agreement. By 12z Monday there
are some subtle difference in the low track for the Gulf and the
next Bering low. The biggest forecast challenge continues to be
dialing in the precipitation and snowfall accumulations across
Southcentral. In the coastal areas, precipitation type also
remains a challenge.

&&

.AVIATION...
PANC...Overnight the cigs dropped below 010 at PANC. On satellite
imagery (Nighttime Microphysics) the Anchorage Bowl and Cook Inlet
are just covered. With the low moving into the Gulf, cigs will
bounce all over the place.  Light winds persist for this TAF
package.

&&

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

The plume of moisture riding along the jet stream form the
Pacific is moving over Southcentral Alaska today and will provide
the snow for the myriad of winter storms warnings that cover the
area. The beginning of the snow has already made it up Cook Inlet
to Anchorage early this morning. However, the way the low near
Kodiak tracks will bring cross-barrier easterly and southeasterly
winds over the Kenai and Chugach Mountains today. This brings us
right to the biggest forecast question: How will this cross-
barrier flow impact snow amounts today for the Kenai Peninsula
northward through the Susitna Valley? Typically, there is
downsloping that will keep snow from occurring on the lee side of
the mountains. However, when the moisture is this deep, it can
often overwhelm the downsloping, though that is a more typical
late summer and Fall situation when that happens. In short, the
snowfall for the interior Kenai Peninsula as well as Anchorage
and Palmer will likely not be very much most of the day today due
to this cross-barrier flow. When it weakens this evening, the
snow intensity will rapidly increase and that is when the big snow
accumulations will occur from this system for these areas: This
evening though early Monday morning. It looks at this point like
the snow may end sooner on Monday morning for these areas as well
and not persist well into the afternoon due to the 500 mb trough
moving east of these areas by noon Monday.

The western Kenai Peninsula near Cook Inlet is a bit of a
different story for today. While the cross-barrier
flow/downsloping will occur closer to the mountains, areas near
the Inlet will be back to the upward vertical motion and snow is
expected to be heavy at times today into tonight for Nikiski,
Kenai Soldotna, and along the Sterling Highway southward toward
Ninilchik. In addition, the gusty northerly winds will bring in
periods of blowing snow which will also reduce visibility today
through this evening.

Blowing snow is also expected through Turnagain Pass and Turnagain
Arm today into tonight where visibilities may get down to one
half mile in the snow and blowing snow. Occasional lower
visibilities are also possible.

Periods of heavy snow from late this afternoon into Monday night
is also expected in the Copper River Basin where there is also a
winter storm warning in effect due to the snowfall. Thompson Pass
is at risk for significantly reduced visibilities in blowing snow
from late tonight through Monday night.

The earlier ending time for the snow over much of the area due to
the quicker passage of the 500 mb trough is probably the biggest
change in the forecast from yesterday.

&&

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

Snowfall arrived on schedule overnight as a low rooted within a
deep tropical moisture tap developed south of the Alaska Peninsula
(AKPen). An associated shield of light to moderate snowfall will
continue to pivot across Bristol Bay and the Lower Kuskokwim
Valley north of this low as it heads past Kodiak Island and into
the Gulf today, resulting in a broad swath of additional snowfall
of around 4 to 9 inches across this axis through tonight. Winter
Weather Advisories remain in effect for both Bristol Bay and the
Lower Kuskokwim Valley as the prolonged snowfall event continues
across both of these regions. By tonight, snow will end from west
to east as a push of much colder, drier air begins to work in
from the northwest. Winds will become northwesterly and gustier as
the low exits, perhaps resulting in some minor blowing and
drifting of the fresh snowfall after falling snow shuts off.

Most of Monday should stay fairly clear and cold as a shortwave
ridge brushes past ahead of the next system of interest
materializing over the Bering Sea. By Monday evening, a front
associated with another Bering low will approach the coastline,
resulting in rapidly increasing southeast winds as another batch
of snowfall moves inland from southwest to northeast. This front
does not appear likely to drive a particularly warm air mass back
in as it encroaches on Southwest, but some mixing with or
changeover to rain will again be possible near the immediate
coastline across Bristol Bay. Blowing snow will likely be an issue
Monday night along the Kuskokwim Delta Coast as the front
initially approaches as falling snow and combines with southeast
winds gusting up to 45 mph. Significant blowing snow is unlikely
to last for an extended period, however, with the front weakening
and stronger winds diminishing across the Kuskokwim Delta by early
Tuesday morning as the parent low pushes onshore. Farther south,
strong westerly and onshore winds will push into Bristol Bay early
Tuesday, potentially resulting in abnormally high water levels
across portions of the Bristol Bay coastline until winds subside
later in the day. Light snowfall will meanwhile spread across more
interior portions of Southwest on Tuesday, with snowfall then
ending area-wide from west to east Tuesday night as the low exits
into the central Interior.

&&

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

Relatively calm conditions exist across the Aleutian Chain and
Pribilofs for the moment, with most of the southern mainland
feeling the effects of the more active pattern. Cold northwesterly
flow around a shortwave ridge advancing across the Bering will
help drive up gusty gap winds along and south of the eastern
Aleutians and Alaska Peninsula by this afternoon into tonight,
with 40 to 50 mph gusts possible out of bays and passes on the
Pacific side. To the west, the next noteworthy system will cross
the western Aleutians into the Bering by tonight, sending winds up
to gale force and light to moderate rain across as its occluding
front progresses along the Aleutian Chain. A brief period of snow
will be possible as the front approaches the Pribilofs early
Monday morning before low level temperatures warm and change
falling precipitation with the passing front to rain. As the low
and attendant front approach Southwest late Monday into Tuesday
morning, a core of gale force winds with gusts to storm force will
develop on the south of the center, advancing along and north of
the eastern Aleutians into the Alaska Peninsula through Tuesday.
Another relative break in the pattern is likely by Tuesday night
as the low weakens and moves northeast into the southern mainland.

&&

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

Very active weather looks to continue throughout southern Alaska
and Bering Sea in the long term. The main features of concern are
a high amplitude trough over the Bering and north Pacific and a
Rex Block from British Columbia south to the West Coast. The main
uncertainty in the forecast is related to the interaction of the
storm developing over the north Pacific on the southern edge of
the trough axis and the blocking ridge as it moves east. With the
high amplitude trough/ridge pattern, ample warm air and an
atmospheric river are expected to move north into the southern
Mainland. Right now deterministic guidance has two main storm
tracks, one through the eastern Bering and into the Interior and
the other into Bristol Bay and the Gulf of Alaska. The east/west
position of the low will determine precipitation type midweek for
both Southcentral and Southwest. The ECMWF and Canadian solutions
show a more amplified solution with a low farther to the west
(eastern Bering and Interior Track), which would lead to rain
across the southern Mainland Wednesday and Thursday, with chances
for snow on the backside as the system occludes. The GFS solution
has a more easterly storm track, which would lead to heavy snow
over the Kuskokwim River areas, rain for Bristol Bay, and mixed
precipitation for Southcentral. The forecast is highly uncertain
and pertains in many ways to the north/south positioning of a low
moving across the southern Mainland on Tuesday, with the more
southern solution helping to keep temperatures aloft cooler and
visa versa. This storm will likely be very impactful, but the
question of how it will be impactful (rain vs snow) is to be
determined.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WSW 101 111 141 145 121 125 152 161.
MARINE...Storm 119 130 132. Gale 150 155 160 165 170 172 173 174
175 176 177 178 179 180 412 413 414 120 121 125 131 138 139.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
LONG TERM...CJ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
209 PM AKST SUN DEC 11 2022

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

0706 AM     SNOW             TALKEETNA, AK           62.23N 150.07W
12/11/2022  M0.5 INCH        MATANUSKA-SUSITNA  AK   PUBLIC

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
210 PM AKST SUN DEC 11 2022

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

0956 AM     SNOW             TALKEETNA, AK           62.23N 150.07W
12/11/2022  M1.1 INCH        MATANUSKA-SUSITNA  AK   PUBLIC

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
211 PM AKST SUN DEC 11 2022

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

0942 AM     DENSE FOG        KODIAK CITY, AK         57.81N 152.38W
12/11/2022                   KODIAK ISLAND      AK   PUBLIC

            CORRECTS PREVIOUS DENSE FOG REPORT FROM 1 NE
            KODIAK.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
214 PM AKST SUN DEC 11 2022

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

1005 AM     DENSE FOG        KODIAK CITY, AK         57.80N 152.38W
12/11/2022                   KODIAK ISLAND      AK   PUBLIC

            SPOTTER ESTIMATED DENSE FOG LESS THAN 1/4
            MILE.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
215 PM AKST SUN DEC 11 2022

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

1011 AM     SNOW             NIKOLAEVSK, AK          59.77N 151.60W
12/11/2022  M4.2 INCH        KENAI PENINSULA    AK   PUBLIC

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
216 PM AKST SUN DEC 11 2022

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

1105 AM     SNOW             NIKISKI, AK             60.71N 151.37W
12/11/2022  M11.5 INCH       KENAI PENINSULA    AK   PUBLIC

&&

ED