Small Craft Advisory 792, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
943 PM AKDT Wed Oct 23 2019

.ANALYSIS AND UPPER LEVELS...
There is a large vertically stacked low centered near King Salmon.
The surface low is currently near 967 mb and slowly weakening.
Considerable showers associated with this low are occurring from
the central Bering eastward through the southern mainland. There
is an upper level ridge over northwest Canada. This is keeping
fairly strong southerly flow to the east of the low. This is
causing some of the showers along the north Gulf coast are to be
fairly heavy, especially along the Kenai Peninsula. There is a
strengthening low to the southwest of the western Aleutians which
is rapidly moving eastward, and this will become a major factor in
the weather over the next few days.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement through Friday
afternoon. There are some forecast challenges dealing with exactly
how the model forecasts will translate into the sensible weather
especially with the showery nature of the precipitation. Therefore
the forecast confidence is near normal.

&&

.AVIATION...
PANC...VFR conditions are most likely through Thursday afternoon.
There is a chance of some MVFR ceilings with showers beginning
late tonight. Gusty southerly winds will diminish later tonight.

&&

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

A powerful storm force low has made landfall this afternoon with
the main low center in Bristol Bay. The storm force front has
moved inland, so the strongest winds have already occurred along
the coast with gusty winds expected to continue across interior
locations through tonight before rapidly subsiding tomorrow as the
surface low weakens and drifts east toward the ALCAN. Showery
weather will persist mainly along the coast and over the higher
inland mountains with only sporadic sprinkles/inland showers.

Thu night a second shortwave trough will dig into the Susitna
Valley, and in conjunction with weak cold air advection, may
support a mix of snow across the Susitna Valley and south into
Anchorage. A brief dry period develops Friday evening before a
more substantial rain event develop for the weekend.

&&

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

A strong low centered over Bristol Bay will continue to work its
way inland this evening. Northerly gale force winds will persist
along the coast overnight before diminishing by Thursday morning.

A Special Weather Statement (SPS) has been issued for possible
high seas along the Bering side of the Alaska Peninsula coast.
With continued northerly flow, coastal erosion is possible from
Port Moller to Egegik, including Port Heiden, starting this
afternoon through Thursday evening. Please see the SPS for more
details.

Rain will persist over the greater Bristol Bay area this evening.
Farther north over the Kuskokwim Delta, colder, northerly flow on
the backside of the low has allowed for precipitation to fall as
snow. As the low center continues to move inland on Thursday, more
widespread northerly (colder) flow is expected with snow showers
likely over the Kuskokwim Delta region before tapering by
Thursday evening. Accumulations will be confined to the mountains,
though trace amounts are possible. Another chance of snow showers
for the Kuskokwim Delta Coast arrives Thursday evening when an
upper level shortwave moves inland, bringing trace amounts to
Nunivak Island and along the Kuskokwim Delta Coast from Kipnuk to
Hooper Bay. Reduced visibility is possible as these snow showers
may coincide with the gusty northerly winds. By Friday afternoon,
another front associated with a large Bering low approaches the
southwest coast. This next system will be a bit of a pattern
change for the weekend with warm, moist southerly flow expected.

&&

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

A storm force low centered over Bristol Bay continues to move
inland. Northerly gales will continue over the eastern Bering
before diminishing Thursday morning. The next big story for the
Bering is another incoming storm force low. The leading front
arrives over the western Aleutians Thursday morning, bringing
easterly gale force winds and rain. The low center is expected to
track south of the Chain, with the leading front reaching the
Pribilofs late Thursday/early Friday morning. This low will
initiate a bit of a pattern change with warm southerly flow and
heavy rain spreading across the Aleutians through Saturday.

&&

.MARINE (Days 3 through 5)...
Over the Gulf there is good model agreement and good confidence
in southeast gales on saturday that will diminish to small crafts
Sunday and Monday. There is low confidence that storm force winds
may be present around the Barrens Saturday and that gales could
last into Sunday. Out west there is high confidence of storm force
winds over the western Bering/Aleutians with a low chance of
storm force winds on Sunday. There is decent agreement that winds
will taper down into Monday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast, beginning Saturday, has ridging over the
eastern Gulf extending north over the eastern mainland. To the
west, a storm force low sits south of the central Aleutians that
will track north into the Bering through the weekend. This setup
results in an atmospheric river developing between the low and
ridging over the Alaska Peninsula with a strong push of warm air
in addition to the moisture. The models are struggling with how
quickly the atmospheric river will track east. This lowers
confidence in where the heaviest rain will be and for any
potential flooding problems that could develop along the Gulf
coast. The biggest impact would be if it stalled over a single
area for an extended period of time. For now, it looks to stay on
a steady track to the east through the week, but guidance is
struggling with that progression.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storms 131 131 150 174 177 178 411 413.
         Gales 119 120 160 165 170-173 175 176 180 181 185 351 352 412
               414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...DK