Small Craft Advisory 161, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
545 AM AKST Sun Feb 16 2020

.ANALYSIS AND UPPER LEVELS...

An upper level low centered over the western Aleutians continues
to move eastward into the Bering as it is steered by a 150 kt jet
south of the Aleutian Chain. A second low centered east of
Adak is lifting into the Bering this morning and its leading front
is bringing rain and gusty southerly winds to the eastern
Aleutians. An upper level ridge over the mainland is beginning to
amplify as the incoming Bering low forces it eastward.

&&

.MODEL DISCUSSION...

Models remain in good agreement through the short term. Solutions
continue to support the development of a storm force low moving
into the eastern Bering Monday morning. By Monday night, models
are suggesting a second low forms in the southern Gulf and lifts
northward over Southcentral. The track and strength of this Gulf low
vary greatly, as well as the possible interactions this low will
have with the Bering low. Overall, there is high confidence that
much of the forecast area will have eventful and impactful weather
for the start of the workweek.

&&

.AVIATION...
PANC...VFR conditions and light winds will continue today. A
front approaches late this evening and conditions are expected to
gradually trend down to MVFR as light snow arrives.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Sun and
Mon)...
A very complex and active weather pattern is set to take shape
across Southcentral AK. Let's proceed in chronological order.
First, a weak warm front is sliding across the southwestern Gulf
of AK this morning. This will bring a quick shot of snow to Kodiak
Island later today before it transitions to all rain. This front
will then make its way into the southern Kenai Peninsula later
this evening before pushing into Prince William Sound by Monday
morning. As it makes landfall along the coast, precipitation will
initially start as snow with some light accumulations expected.
There could be pockets of blowing snow through Portage Valley and
Turnagain Pass on the leading edge of this front early Monday.
However, as the winds push in, warm air will accompany them. This
should cause the snow to mix with rain, especially at lower
elevations and coastal sites. Farther inland over the Susitna
Valley, the air will remain cold enough to support all snow and
allow for a few inches of accumulation.

Part two of this pattern will be a strong low developing over the
eastern Bering. This low will sling another front on a nearly
identical track across the Kenai Peninsula and eventually into
Prince William Sound. There will not be much in the way of a
perceivable break in precipitation for many of the coastal
locations due to the abundant moisture and deep southerly flow.
This system will bring strong southeast winds to Turnagain Arm,
Anchorage Hillside, and parts of the Matanuska Valley. These
winds are expected to push in during the day Mon and eventually
into the Anchorage Bowl late Mon night. Warmer temperatures will
ride in with these winds as they serve to mix down some of the
warmer air aloft. The winds will also serve to downslope many of
these same areas, keeping them mostly dry. The western Susitna
Valley will be a different story. Cold air will hold on up there
and the southerly flow will create impressive snow rates. Several
inches of new snow accumulation are expected up there through
Tuesday morning.

Finally, the third part of this complex pattern will be a cold
front entering the area from SW Alaska late Monday through early
Tuesday. Deep southerly flow will allow for widespread moderate
to heavy precipitation to continue across much of Southcentral,
especially in coastal areas. As the cold air moves in, this should
change all of the precipitation to snow. There could be
significant accumulations through Turnagain Pass, Susitna Valley,
and Thompson Pass. Winds will remain gusty in some locations, so
blowing snow will also remain a threat. This set-up will also
provide the Anchorage Bowl its best chance for accumulating snow.
Due to the complexity of this system and disagreement between the
forecast models, it is still a bit too early to nail down exact
snow accumulations. Interested parties should closely monitor the
forecast.

&&

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

Light snowfall continues across Southwest Alaska this morning as
the result of a front diminishing across the region. A brief
period of dry conditions will move in this afternoon before the
next system moves in later today.

A warm front moving across the Alaska Peninsula by early afternoon
will bring warmer temperatures with a mix of rain and snow into
the greater Bristol Bay area as it lifts north through the evening
hours. This front could bring an inch or two of new snowfall
accumulation to the region before a second front moves into these
same areas overnight tonight into Monday. Expect any rain or rain/snow
mix to transition to snow with the second front as cooler
temperatures wrapped around the backside of the associated low
make their return to the region late Monday into Tuesday. The
possibility of blowing snow conditions cannot be ruled out during
this time with snowfall and gusty winds. However, no products
have been issued at this time for the Bristol Bay area, but will
be considered in future forecasts as models come into better
agreement with the placement of the associated low.

Over the Kuskokwim Delta, models all agree on blizzard conditions
in this two part system, leading to the issuance of a Blizzard
Warning for areas west of Bethel. The first front will move along
the Kuskokwim Delta coast this evening. Strong winds and falling
snow will cause reduced visibility in blowing snow. The second
front will approach the coast early Monday morning, which will be
when the worst blizzard conditions are expected, with visibility
dropping to a quarter mile at times. By Monday afternoon, the
strongest winds will diminish as the low center weakens and moves
inland, but expect the snow and blowing snow to continue through
early Tuesday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Active weather remains over the Bering today starting with a pair
of lows along the Aleutian Chain. The first low the central Chain
will weaken throughout the day as it lifts north of the Pribilofs
by this evening. The second low near Shemya is strengthening as
it moves towards Adak by Monday morning.

A rapidly deepening low quickly moves in from the North Pacific
near Dutch Harbor by late this evening. This continues to be the
biggest forecast challenge in terms of position and strength. The
High Wind Watches remain in effect for the Alaska Peninsula and
Eastern Aleutians, with the biggest impacts expected between Dutch
Harbor and King Cove starting this evening, with the potential to
see gusts to 80 mph. These watches have been extended in time due
to elevated winds expected to continue through Monday as colder
air gets wrapped into the back side of the low.

The position of this low keeps trending westward, keeping it
closer to the Pribilofs and slightly strengthening from the
previous models runs. This will likely cause blowing snow
conditions for the Pribilofs starting Monday afternoon through
Tuesday. No hazardous winter weather products have been issued for
the Pribilofs, but will be considered for this afternoon's
forecast package. Residents should remain on alert for blowing
snow conditions and cold temperatures returning to the island in
the coming days. The associated low will then move inland over
Southwest Alaska by Tuesday afternoon.

&&

.MARINE (Days 3 through 5/Tuesday through Thursday)...The extended
forecast begins on Tuesday with a deep system in the eastern
Bering Sea. Widespread gales can be expected over much of the
Bering with this system as well as freezing spray concerns.
Another system enters the area on Wed/Thur and looks to come west
to east, possibly tracking just south of the Aleutians. No matter
the storm track, the secondary system will bring a colder air mass
to the Bering Sea along with freezing spray concerns and prolonged
northerly wind.

&&

.LONG TERM FORECAST (Days 4 through 7/Wednesday through
Saturday)... An active storm pattern will be taking shape in the
extended period. Guidance is pointing at a slightly different
track than what we've been experiencing, just south of the
Aleutians into the Gulf of Alaska as opposed to the north Pacific
into the Bering Sea. The setup will bring more active weather to
Southcentral Alaska. The focus for this time period will be a
front stalling out from northwest to southeast over the
mainland/Gulf of Alaska on Tuesday. Guidance is pointing to the
development of a strong low pressure system along this boundary
in the Gulf, tracking into Prince William Sound. The main concerns
with this track will be snowfall potential in Anchorage and
Matanuska Valley, as well as Valdez area. Behind that system, a
system from the Aleutians will move into the Gulf of Alaska late
in the week. No matter the exact storm track, look for another
shot of Arctic air coming back into the area.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch...181, 185. Blizzard Warning...155.
MARINE...Storms: 155, 165, 170, 172, 180. Gales: 127, 130, 132,
150, 160, 171, 173, 174, 177, 178, 179, 181, 185, 352, 412, 413,
414. Heavy Freezing Spray: 139, 185.
. FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...MTL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1213 PM AKST SUN FEB 16 2020

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

0756 AM     EXTR WIND CHILL  NUNAPITCHUK             60.91N 162.44W
02/13/2020  M-43 F           BETHEL             AK   ASOS

            ASOS RECORDED A WIND CHILL VALUE OF -43F.

&&

ED