Small Craft Advisory 908, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
728 AM AKST Fri Nov 29 2019

.ANALYSIS AND UPPER LEVELS...

A strong upper level low is currently centered over the Kamchatka
Peninsula. The associated surface low is bringing gusty
southwesterly winds and moderate rain to the western Aleutians
along its front. Downstream, a deep upper trough extends from the
Seward Peninsula south to the Alaska Peninsula. This is creating
decent rising motion and surface convergence and as such, snow is
falling along the Bristol Bay coast just east of the trough axis.
Southeasterly flow on the east side of a North Pacific low is
likewise bringing snow across the northern Susitna Valley and
higher elevations, with rain farther south and at lower
elevations including the southern Kenai Peninsula and Prince
William Sound. As the flow pattern is cross-barrier, downsloped
areas are currently seeing minimal precipitation.

&&

.MODEL DISCUSSION...

Models have generally come into better agreement from the
previous runs, although uncertainty still exists as GFS remains
the warmest solution by several degrees in some locations. Exact
timing and potential snow amounts across Southcentral this weekend
remain in question as well. The 06z NAM is not as much of an
outlier as the previous run, but it does match better with the
most recent ECMWF and GFS, tracking the approaching low over
Bristol Bay and eastward over Anchorage. The latter models remain
the preferred solutions as they have had the best run to run
consistency.

&&

.AVIATION...

PANC...VFR conditions will generally persist through Saturday
morning. Brief LIFR ceilings are possible this morning through
approximately sunrise. Wind shear will remain an issue as light
northerly winds will continue at the surface, while relatively
stronger southeasterly winds persist aloft.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

A weak upper trough, associated with a stationary low south of
Kodiak and a front extending north across the Gulf and Southcentral,
moves east later today. Strong SE cross-barrier flow over the Kenai
and Chugach Mountains will keep precipitation to the lee (west) to a
minimum today. Weak southerly flow over the Susitna Valley will keep
some light snow going through today. A second and stronger upper
trough and surface front move into Southcentral on Saturday.
This feature should bring widespread precipitation. Snow will be
likely over the Susitna Valley and surrounding higher elevations.
The low level cold air lags some and will not likely get over the
Matanuska Valley to Anchorage/Cook Inlet corridor until late in the
afternoon. So expect precipitation in these areas to start as rain
or or mix and shift to mostly snow in the afternoon. There is still
a bit of uncertainty on how quickly the cold air arrives which will
make for a challenging snow forecast. The upper trough and surface
front move through fairly quickly, but drying will be short lived as
yet another front quickly ushers in moisture late Saturday
night/Sunday morning.

Gales will likely continue across the Gulf through tonight along
with strong gap winds from Portage Valley to along Turnagain Arm.
Winds should diminish in these areas Saturday before the next system
approaching from the west brings increasing winds to the western
Gulf/Kodiak Island Saturday night.

&&

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

A cold upper trough over the western half of Southwest Alaska
continues to anchor a deformation zone aloft as warm, moist North
Pacific air continues to advect northward. This region is
continuing to dump prolific snow across the Alaska Range into
parts of the Lower Kusko Valley and interior Bristol Bay. The
deformation zone will weaken and move toward the Alaska Range
before falling apart tonight, but not before an additional 4-8"
falls across the aforementioned areas. Attention then turns to a
fast moving occluded front which will reach the Kusko Delta coast
this evening and tonight, bringing a quick hitting 1-3" inches of
snow to the Delta before it rapidly falls apart as it moves inland
through Saturday morning.

The next major feature of interest is a developing North Pacific
low forming along an impressive arctic front. This low is now
projected to move into the Eastern Bering Sea and Bristol Bay as a
strong gale force low sometime Sat afternoon and through the
night. The track and strength of this low still remains rather
uncertain, which really complicates this forecast because of the
compact nature of the low. Long story short, it is becoming
increasing likely this low will bring a band of accumulating snow
along this front across parts of Southwest Alaska this weekend,
with the possibility of advisory level snow amounts (greater than
6 inches) along with potential blowing snow. The 00z and 06z ECMWF
and Canadian models favor a slower and much stronger low (near
storm force) while the NAM remains the farthest south, weakest,
and fastest, with the GFS somewhere in the middle. Given the
uncertainty, the GFS was favored since it was a middle ground
solution. Stay tuned for further details as this potential storm
develops.

&&

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

A powerful high end gale force occluded front is rapidly moving
east across the Bering Sea, and is moving into the Pribs and
Eastern Aleutians, and will reach the coast by this evening.
Strong cold air advection snow showers behind this front will
follow through Fri night.

Attention quickly turns to a developing strong gale force low
which moves into the Central Aleutians late tonight then moves
into Bristol Bay by Sat night. There is still uncertainty with
this low, but expect rain/snow turning to rain along the chain,
along with gale force winds and possible storm force gusts by the
time the low reaches Bristol Bay. This low moves inland Sunday
morning, leaving behind it a broad region of cold air advection
snow showers and near gale force westerly winds.

&&

.MARINE (Days 3 through 5)...

Bering/North Pacific/Bristol Bay: On Sunday, low pressure east of
the Pribilof Islands will move towards Bristol Bay bringing small
crafts and gales to the region. This is a very progressive pattern.
Another low will quickly enter the Bering. The models differ on the
intensity of the winds associated with this second low, but at the
very least expect gusty winds and enhanced seas. The current
thinking is that this second low will produce westerly small-craft
winds with embedded gales will develop from the western Aleutians
Monday to the AKPEN by Tuesday as a one area of low pressure over
the central Bering and a second near Shemya on Monday move east. It
is possible this second low paralleling the Aleutian Chain deepens
well enough to produce an area of storm force winds around the core.
There is still quite a bit of uncertainty with these systems,
however, the evolution of these lows will be closely monitored.

Gulf Of Alaska: A surface low will move into the Cook Inlet with a
front in the Gulf Of Alaska and the North Pacific. Small crafts and
gales will accompany this system Monday and into Tuesday.

&&

.LONG TERM FORECAST (Days 4 through 7)...

An active weather pattern will continue from the weekend into
early next week as the axis of the upper-level trough slowly
shifts from the Bering to the Alaska mainland. As it does, the
pattern becomes slightly less amplified, allowing a series of fast-
moving shortwaves to track from the Aleutians chain and Bering east
to the Gulf. First up is an area of low pressure over Bristol Bay /
AKPEN late Saturday moving inland Sunday with a secondary low
spinning up in the northern Gulf near the eastern Kenai Peninsula,
moving into Prince William Sound by late Sunday. There is still
quite a bit of uncertainty with this, but guidance is beginning to
convergence on this solution. If true, this would bring a wintry mix
of precipitation into Southcentral Sunday and Monday as colder air
brings to work into the region. Temperatures and precipitation type
will be the biggest challenges with this system, but right now it
appears that there increasing chances for snow in and around
Anchorage by the start of next week.

Farther west, a low over the Bering and a developing low over the
western Aleutians Monday will track east to the Kuskokwim Delta
and AKPEN, respectively, by Tuesday. Again, there is some
uncertainty with the strength of these systems, but it does
appear more likely that rain and gales will impact the Chain
early next week while the Bering low produces some snow for
coastal Southwest Alaska.

As these systems and the upper-level trough slide east, a
northerly flow will develop over the state ushering in colder and
drier air across the Southern Mainland by mid week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 152 161.
MARINE...Storm Warning: 174.
 Gale Warning: 119 120 150 155 170 172 173 176 178 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
MARINE/LONG TERM...PS/TM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1039 AM AKST FRI NOV 29 2019

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

1039 AM     SNOW             1 SSE SLEETMUTE         61.70N 157.17W
11/29/2019  E6.0 INCH        BETHEL             AK   PUBLIC

            SPOTTER REPORTED 6 INCHES OF SNOW OVERNIGHT.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1040 AM AKST FRI NOV 29 2019

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

1039 AM     SNOW             2 WSW ILIAMNA           59.76N 154.91W
11/29/2019  E3.0 INCH        LAKE AND PENINSULA AK   TRAINED SPOTTER

            ILIAMNA FSS REPORTED 3 INCHES OF SNOW WITH 2
            OF THE 3 INCHES FALLING OVERNIGHT.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1134 AM AKST FRI NOV 29 2019

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

1133 AM     SNOW             2 NNW KOKHANOK          59.44N 154.77W
11/29/2019  E12.0 INCH       LAKE AND PENINSULA AK   PUBLIC

            SPOTTER REPORTED 12 INCHES OF SNOW
            ACCUMULATION BETWEEN LAST NIGHT AND THIS
            MORNING.

&&

ED