Small Craft Advisory 1001, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 AM AKST Mon Dec 17 2018

.ANALYSIS AND UPPER LEVELS...

A deep, strong upper level low is centered right over the heart of
Southwest Alaska this morning. Thus, for much of Southwest Alaska,
conditions are clear and cold. Upper level lows signify cores of
cold air, and thus, conditions are cold in and around them. There
are some localized areas of low stratus and fog in that area as
well. The cold spot so far this morning in all of Southwest Alaska
is King Salmon, where temperatures have reached negative 20.
Elsewhere, most areas are within a few degrees of negative 10.

The story further east across Southcentral is the very active
weather pattern, causing numerous areas of precipitation across
the area. While temperatures are much warmer than over Southwest
Alaska, all communities except those right along the Gulf Coast
are in the teens and 20s, with snow as the dominant precipitation
type. Radar is showing an area of light to moderate snow from
Anchorage north into and the Susitna Valley. All of the steady
snowfall activity is expected to lift to the north this morning.
Precipitation is ongoing across Prince William Sound as well with
rain around Cordova and snow through Valdez and Thompson Pass.

&&

.MODEL DISCUSSION...

The models remain in very good agreement regarding the placement
of the large-scale highs and lows over the area and even their
larger scale associated fronts as well. This helps improve
confidence on weather factors such as the wind. Precipitation
placement is the number one challenge throughout the next couple
days. All the models show the upper level low currently over
Southwest Alaska slowly shifting south and east into the western
Gulf by Tuesday night. This keeps much of Southcentral in the area
of lift, which is favorable for precipitation. However, timing the
precipitation, and any bouts of heavier snow inland is nearly
impossible. Thus, forecast confidence is high that it will
precipitate, but confidence in where and how much is much lower.

&&

.AVIATION...
PANC...Snow showers very early this morning will diminish in the
next few hours as the disturbance causing them lifts to the
north. Low level moisture will persist behind it however, leading
to expected MVFR ceilings throughout the day. Very light snow
showers are possible today, which may produce very minor
accumulations, but nothing as heavy as what's going on currently.
This evening, ceilings may lower further, perhaps restricting
visibility at times. More snow showers and/or steady light snow
are in the forecast for Tuesday afternoon into the overnight.

&&

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

Upper level southerly flow will continue through tonight with the
main low over southwest Alaska. The front over the area this
morning will move north and dissipate during the day. Snowfall
will mostly end by this afternoon over most of Southcentral.
However, plenty of residual moisture will combine with cold
advection to keep some chances of snow through tonight. On Tuesday
the southern portion of the southwest Alaska low will "pinch off",
push into the western Gulf and spin into a significant upper low.
This will bend the flow from south to southeast, and begin to draw
more moisture from the eastern Gulf. As this moisture meets the
cold air, it will form a somewhat organized system in the northern
Gulf. This will bring increasing chances of snow to Southcentral
Tuesday and Tuesday night. This will also tighten up pressure
gradient as low pressure develops in the northern Gulf and the
cold surface high pressure over the mainland strengthens. This
will increase winds across the Gulf, especially in the the outflow
areas such as Kamishak Bay.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Monday
through Wednesday)...
The forecast for southwest Alaska today is persistence based. Cold
air is in place and doesn't look to be going anywhere in the short
term. Temperatures will bounce up and down with the movement of
cloud cover, with temperatures dropping as cloud cover departs an
area. One change that was made in the forecast was warming the
bitterly cold overnight lows the next couple of days for inland
areas. Some model guidance is still going for around -30F, but did
not see any indications we will actually get that cold. So, warmed
temperatures to about what they are now. Some light snow is still
expected for areas in southwest AK as well, but little
accumulation is expected.

&&

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

Northerly flow with snow showers is expected to continue through
Tuesday for the Bering Sea and Aleutian Islands. The sustained
northerly flow has pushed cold air south of the Aleutians. Winds
coupled with cold temperatures means widespread areas of freezing
spray in the Bering Sea. On Tuesday, a stronger low pressure
system will move into the Aleutian Island chain, warm temperatures
and bringing strong winds with it. Wind speeds should barely
reach storm force in the western Aleutians, with winds weakening
to below gale force as the system moves across the central
Aleutians Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
By Wednesday, the cold upper level low will be centered over the
Barren Islands with an upper level trough and accompanying deep
cold air mass persisting over western Alaska and the eastern
Bering. Additional cold air over Kodiak Island and the western
Gulf will rotate east and north to spread across the Gulf and into
Southcentral Alaska as well, with troughs rotating around the
broader low continuing to bring additional periods of snow with
them. On Thursday, the upper low will stretch out to a trough and
lift north to be centered over Prince William Sound and northern
Gulf with precipitation becoming more limited to these areas and
then tapering off Thursday night as the trough dissipates.

Over mainland Alaska, a cold, elongated upper level low will
stretch across much of the state through Thursday night as a deep
north Pacific low tracks well south of the western Gulf. As the
north Pacific low and an accompany frontal system turns to the
northeast and tracks towards the southern Gulf Friday and
Saturday, the mainland upper trough will retrograde back to the
west to become centered over western Alaska and the eastern
Bering. Further to the west, a couple of developing lows will
track over the western Aleutians Thursday through Friday morning,
followed by a third low tracking north and then west through the
central Aleutians Friday night and Saturday.

For Sunday through the first half of next week, the large arctic
low will persist centered over the northern Bering with cold upper
troughing extending into western Alaska. Low pressure systems will
continue to rotate through the central and western Aleutians.
While the main jet and stronger storm track will remain well south
of the Gulf and directed at the Pacific Northwest, additional
troughs and weaker low pressure systems breaking off from this
will track north and rotate through the Gulf as well through early
next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 145.
MARINE...Storm Warning: 178.
Gale Warning: 130 132 150 177 411.
Heavy Freezing Spray Warning: 160 180-185.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
LONG TERM...JR

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
925 AM AKST MON DEC 17 2018

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

0919 AM     SNOW             20 NNW HOPE             61.15N 149.93W
12/17/2018  M2.8 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL SNOWFALL. 0.21 IN OF SWE.
            CURRENT SNOW DEPTH AT 11.5 IN.

0918 AM     SNOW             EAGLE RIVER             61.32N 149.54W
12/17/2018  M0.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL SNOWFALL.

0918 AM     SNOW             NEAR E EAGLE RIVER LOOP 61.32N 149.54W
12/17/2018  E0.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL.

0917 AM     SNOW             1 NW SOLDOTNA           60.50N 151.10W
12/17/2018  M4.5 INCH        KENAI PENINSULA    AK   PUBLIC

            STORM TOTAL SNOWFALL SINCE SUN.

0915 AM     SNOW             NATIONAL WEATHER SERVIC 61.16N 149.98W
12/17/2018  M3.8 INCH        ANCHORAGE          AK   PUBLIC

            STORM TOTAL SNOWFALL SINCE SUN MORNING.

0733 AM     SNOW             LAKE OTIS / HUFFMAN     61.10N 149.82W
12/17/2018  M4.1 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL SNOWFALL SINCE SUN. LIGHT
            FREEZING DRIZZLE AT THE TIME OF OBSERVATION.

0644 AM     SNOW             2 SW CAMPBELL           61.16N 149.94W
12/17/2018  M3.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            STORM TOTAL SNOWFALL.

&&