Small Craft Advisory 866, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
908 PM AKST Sun Nov 4 2018

Update to the LongTerm Forecast

.ANALYSIS AND UPPER LEVELS...
Ridging continues to dominate mainland Alaska with the axis
extending across the Alaska Peninsula and through Bristol Bay and
the Lower Kuskokwim Valley. On the east side of the ridging a
shortwave is pushing south through Southcentral Alaska which has
enhanced outflow winds in the gaps around the north Gulf coast.
West of the ridge, a weak front is pushing in over the Kuskokwim
Delta and even further out west a front is bringing rain to the
western Aleutians as it tracks east.

&&

.MODEL DISCUSSION...
The models have a fairly good handle on the main features in the
short term but are struggling with timing and location of the main
lows and fronts in the mid term. The 12Z runs are in better
agreement with the low moving into the Gulf Tuesday night but are
struggling with the timing of its associated front as it
approaches the north Gulf coast. There is also disagreement on
timing and location of a low moving into the western Bering
Wednesday with the NAM furthest north and the EC furthest south.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

Dry conditions persist through Tuesday across Southcentral as a
surface ridge across the central interior shifts to the Alcan
border. An upper level wave dives south toward the gulf tonight as
the upper ridge axis aligns over the west mainland. This energy
forces a tighter pressure gradient along the coast bringing an
increase of winds for north to south oriented gaps. These winds
should slacken Monday afternoon with the upper ridge shifting
across the southern Gulf.

The next front moves up to the southern Gulf late Tuesday
afternoon, spreading rain across the southern waters along with
gusty easterly gales. There is still a bit of uncertainty on the
track and timing with this quickly developing storm system. The
front is expected to move to the coast by Wednesday afternoon as
the surface low tracks northeast. Upper level short waves
propagating northwest from the storm core will allow a few showers
to move inland. Precipitation along the gulf coastal areas will
be rain with this warm core system with showers inland falling as
snow with a cold air mass in place.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Today
through Monday Night)...

A weakening trough approaching the coast is pushing a band of
clouds west to east from Bristol Bay north to the YK Delta this
evening. Moisture is very limited with this system; however any
precipitation that does reach the below-freezing surface will
fall through a layer of warm air aloft, resulting in pockets of
light freezing drizzle from Dillingham north to Bethel through the
evening hours. Very minor ice accumulations are possible around
the Kuskokwim Delta, where the most persistent drizzle is
expected to fall.

The warmer air moving in aloft over Southwest Alaska is the
result of a ridge in the upper-levels. This ridge will help
stabilize the atmosphere and reduce mixing near the surface. A
lack of wind along with only partly cloudy skies across the Lower
Kuskokwim Valley and Bristol Bay tonight will help produce areas
of fog overnight. Fog may also develop in the Kuskokwim Delta, but
it will likely be the result of the aforementioned front and
freezing drizzle. A second front will slide across the Kuskokwim
Delta Monday night and into the southwest interior Tuesday.
Warmer air out ahead of this system is expected to keep the
precipitation type mostly rain, especially around Bristol Bay and
the Kuskokwim Delta. Locations well inland and along the higher
terrain can expect a light accumulation of snow.

Another potential hazard for the late Monday through Wednesday
time frame is an expected prolonged period of steady south to
southwesterly winds moving into the coast, which may have impacts
as far as high water levels are concerned.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Today
through Monday Night)...

The main weather story for the Bering is a deepening Kamchatka low
sweeping an occluded front across the western Bering and
Aleutians tonight bringing rain and widespread gales to the area.
This low will swing southeast tonight behind the front, leading
to a second area of widespread gales and even storm force winds
over the western and central Bering Monday. The northwesterly
track of the low will keep the strongest winds well north of the
Aleutian Chain but will bring gales to the Pribilofs late Monday.
By early Tuesday, the low will move into the northern Bering as
the core of gale-force winds brush past Nunivak Island. Behind
the low, colder air will slide southeast from eastern Russia and
move over the Bering for Tuesday and Wednesday. The next
Kamchatka low then begins to move east late Tuesday with another
round of rain and gales across the western Bering and Aleutians
overnight Tuesday into Wednesday as its associated front sweeps
across the region.

&&

.LONG TERM FORECAST (Days 3 through 7/Monday through Friday)...

At the onset of the forecast period, there is a storm southeast
of Kodiak and an organized system east of Kamchatka. Models seem
to be improving and converging on both the low in the Gulf Of
Alaska and the new low in the Bering. There are some minor
differences with timing and intensity for both lows, but there is
a confidence boost for the longterm. Both of these storms will
bring another round of enhanced/gusty winds and a well organized
precipitation shield. Thursday the surface low for the gulf storm
will be just south of Middleton Island moving northeast. An
inverted trough will develop over Prince William Sound and into
the Copper River Basin. By Friday, the the surface low will have
rapidly weakened and pushed off to the east. In the wake of the
frontal passage ridging will build over the Gulf of Alaska. The
main weather producer with the the frontal boundary pushing across
the Aleutians/Bering and into southwest AK by the weekend. There
is a secondary impulse on the back side of the Bering low which
the models ping into.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm 411 412. Gales 177-181 185 413.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...PS