Small Craft Advisory 768, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
437 AM AKDT Tue Oct 15 2019

.ANALYSIS AND UPPER LEVELS...

A strong 958 mb low (remnant Hagibis) centered west of St.
Matthew Island continues to slowly move northward. This low has
brought hurricane force gusts and high seas to the Bering waters
overnight. A front associated with this low has stalled along the
Southwest coast, inhibited from moving inland by a persistent area
of high pressure in place over the Mainland. Behind the low, cold
air is streaming in from the northwest. Meanwhile over the Gulf,
a complex low has brought gusty easterly winds and rain to Kodiak
Island. An inverted trough associated with this low has begun to
lift northward and is approaching the northern Gulf coast this
morning.

&&

.MODEL DISCUSSION...

Forecast models continue to be in good agreement regarding the
overall synoptic pattern. Disagreement arises by Wednesday when
model solutions differ on the location of several smaller
circulations over the Gulf of Alaska and their arrival into
Southcentral. Meanwhile over the Bering, a second strong low moves
in Tuesday night. Models struggle to agree on the strength and
track of this low, though current thinking is the low center will
traverse the Pribilof Islands late Tuesday into early Wednesday.

&&

.AVIATION...

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

&&

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

Outflow and gap winds are expected to diminish across Southcentral
today as pressure gradients relax. Broad cyclonic upper level flow
over the NE Pacific/Gulf will continue a support a series of lows
which will generally drift across the Gulf. Positioning of
centers and intensity will be somewhat problematic. However, while
there are differences, common ground can be be found with NE to
NW gales over the western and northern Gulf today and weakening
tonight. Gales will redevelop across the southwestern Gulf
Wednesday afternoon/night as the next front moves in from the
west. Precipitation will spread west across the northern and
western Gulf today with rain at most sea level locations and mix
or snow at higher elevations over the mainland coastal mountains.
Overrunning snow potential across the Chugach into the Matanuska
Valley/Anchorage Bowl on Wednesday morning looks fairly weak.
However, could not rule out flurries or some very light snow
during the morning hours which would then mix with rain during
the afternoon.

&&

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

Precipitation from the frontal boundary has been detected on the
radars at Bethel (PABC) and King Salmon (PAKC) this morning. The
front spans from Hooper Bay to Pilot Point. The models bring the
boundary inland today with light rain making it to Bethel and
Levelock. However, the front loses momentum. A second frontal
boundary will move into the region early Wednesday. Widespread
rainfall is anticipated with coastal communities receiving the
lion's share of the moisture.

&&

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

This morning the surface low anchoring the remnants of Hagibis is
west of St. Matthew Island with an estimated pressure of 958mb.
The models show the surface low moving westward into NE Russia.
The surface low will weaken and the northern portion of the
frontal boundary will undergo the process of frontolysis. The
longwave trough over the Bering has several impulses of shortwave
energy embedded. A second surge of energy will create a new wave
along the baroclinic zone near the western Aleutians. This new low
will undergo a period of rapid intensification today. The new
surface low will track over the Pribilof Islands tonight bringing
another round of strong winds and rough seas. As the forecast
period unfolds, the low will push into western Alaska on Thursday.

&&

.MARINE (Days 3 through 5)...

Bering Sea/Aleutians: Models continue to show discrepancies for
the synoptic setup in the Bering in the Thursday timeframe. In any
case, there continues to be indication that a double barrel low
will set up in the Bering, with one center near Cape Newenham and
the other center in the northeast Bering. It's tough to say which
will be stronger, but models have shown a slight trend deepening
the Bristol Bay/Cape Newenham low. This would likely result in
some gales in the southern Bering and eastern Aleutians Thursday.
Expect mixed seas with combined wave height in the 15 to 20 foot
range... subsiding Friday. A series of disturbances will likely
rotate around the northeast Bering low, thus areas of showers and
small craft advisory conditions are likely through the end of the
week.

Gulf of Alaska: An upper low will cross the AKPEN Thursday and a
surface low will develop near Kodiak Island. The range of
solutions is a bit broader than ideal... the main question is how
far north the low propagates. It's possible that it will bring
gales to the southern outer waters Thursday. Or, it could track
far enough south that stronger winds will be concentrated in the
North Pacific. Either way, elevated winds are likely out of
Kamishak Bay as pressure drops in the Gulf. The pattern looks
generally benign in the Gulf by Saturday, but model discrepancies
compound so it will be important to monitor the forecast.

&&

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

Details in the long term remain murky, as models continue to
struggle with the preceding evolution of post-Typhoon Hagibis.
However, there are some general trends apparent. Low pressure is
likely to settle in the Bering Sea (or perhaps centered off the
west coast) through early next week, and cold air advection in
north flow around the west side of the low will continue showery
unstable conditions over the Bering/Aleutians. The location of the
low center is uncertain, but if it sets up near the west coast,
precipitation and increased southwest winds are likely in its
southern periphery. High pressure in the low levels will persist
over northeastern Alaska, leading to cold, generally dry
conditions inland. However, enhanced cyclogenesis is likely as
modified cold, dry air originating in eastern Siberia spills into
the North Pacific. Thus, expect a series of lows to approach the
Gulf from the west. This will likely bring precipitation and
increased cloud cover to the North Gulf Coast, possibly making it
inland.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch: 195.
MARINE...Storm Warning: 177-179, 185, 412, 413, 414.
Gale Warning: 119, 120, 131, 132, 150, 155, 160, 165, 170-176,
180, 351, 352, 411.
. FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...MM