Small Craft Advisory 859, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKDT Fri Nov 2 2018

.ANALYSIS AND UPPER LEVELS...
An upper level area of high pressure is still in place over the
Alaska mainland today, extending along a negatively tilted axis
from Kotzebue down toward Gulkana. Looking westward, an inbound
960 mb low is currently centered over the central Aleutians. Due
to the close proximity of these two systems, strong, gusty
easterly and southeasterly flow is in place at the surface across
the southwestern Gulf as well as Kodiak Island, the AKPEN, and the
eastern Aleutians. The leading edge of the front associated with
this low is beginning to spread precipitation in across the AKPEN,
coastal areas of Southwest Alaska, as well as Kodiak Island. What
was a triple point low along this front has strengthened in the
southern Gulf of Alaska and is heading toward Southeast Alaska.
This low is moving quickly eastward and elongating (and weakening)
the front as it moves into Southcentral Alaska and into the ridge
of high pressure.

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.MODEL DISCUSSION...
Good synoptic agreement across the models continues today. Even
the issue with the speed of the low tracking across the Gulf of
Alaska has been resolved. Differences generally pertain to the
resolution of smaller features and terrain effects.

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.AVIATION...VFR conditions and light winds will persist. Cloud
cover is expected to keep fog from redeveloping again overnight.

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.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
A strong gale force front is moving north toward the Gulf Coast
this evening with rain impacting Kodiak Island. The front will
clear Kodiak Island soon after this AFD goes out then reach the
southern Kenai then quickly fall apart by Saturday morning. With
the stout interior high pressure in place, precipitation will not
make it far beyond the immediate coast with some higher elevation
light snow. Moderate offshore flow in Prince William Sound will
keep Valdez and Thompson Pass completely out of any snow threats.
The front moves east Saturday with a secondary upper level high
building over the interior. The upper level flow will go northerly
and with cold high pressure in place, this will create another
period of mostly sunny weather with offshore gap winds through
Monday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Today
through Saturday Night)...
The main feature driving the weather across the southwest mainland
through Saturday is the large strong low moving from the eastern
Aleutians to the western Gulf of Alaska Saturday. The main concern
with this front and low is with respect to wind and cross barrier
flow across the Aleutian Mountains and Alaska Range. Cross
barrier down slope flow will serve to limit rain amounts. In
contrast, the upslope regions of the Kilbuck and Ahklun Mountains
will result in precipitation. A weak residual trough from this low
northwest along the Bering Coast persists through Saturday night
followed by a rapidly moving low amplitude weak ridge Sunday. As
we move into Monday we have a large strong low moving into the
northwest Bering Sea. This storm will push a front into the
southwest mainland, although most of the energy and strongest
wind with this storm will focused north of 60N latitude. One
concern for Monday is a long moderate fetch across the Bering Sea
into Kuskokwim Bay. At this time we are only anticipating rises
around a foot over mean higher high water. This will bear watching.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Today
through Saturday Night)...
The strong low over the eastern Aleutians will move off to the
western Gulf of Alaska Saturday. The strong northeast to northwest
wind around the north side of this low will gradually weaken as
the low moves off to the east and weakens. In its wake showers
will be plentiful across the Alaska Peninsula to the Central
Aleutians. This storm will be followed by a weak ridge of high
pressure that will rapidly be replaced by the next strong large
low to impact the Aleutians and Bering Sea. This next storm moves
into the western Bering Sea Sunday with the associated front
sweeping through the western Aleutians with gale to storm force
wind in advance of it. This front rapidly sweeps across the
eastern Aleutians and eventually to the Bering Sea coast, albeit
much weaker south of 60N latitude. The parent low will be in the
northwest Bering sea leaving the Bering Sea and Aleutians in the
west to southwest flow with the main impact being showery
conditions with small craft to gal force wind through Monday.

&&

.LONG TERM FORECAST (Days 3 through 7/Monday through Friday)...
Not much change in the extended forecast today for Anchorage
forecast area. Cold and dry conditions are expected to continue
for the mainland, with storms moving across the Bering Sea through
the end of next week. In the upper levels, a strong ridge over
the mainland maintains its hold, keeping a strong low over the
western Bering Sea. This low will track northward through the
Kamchatka Peninsula, bringing gale force winds to the Bering Sea
through Wednesday, but relatively few impacts otherwise. Although
the front from this storm is anticipated to move over the mainland
on Wednesday, it should be relatively weak and precipitation is
not expected to make it very far inland.

As the Bering Sea low weakens, another low is expected to approach
the area from the northern Pacific. Again, the upper level ridge
should help deflect this feature off towards the east. Yesterday's
model runs were in more disagreement on what would happen with
this low, but today, they've come more into alignment, with the
surface low crossing the Gulf of Alaska toward Yakutat late
Wednesday and into Thursday. This should bring some outflow winds
to the Southcentral region, but precipitation impacts are expected
to be confined to the Gulf Coast.

For the end of next week, models are picking up on a stronger low
pressure system crossing the Bering Sea closer to the Aleutians
than the storm we see moving through the Bering earlier in the
week. Models were indicating a similar solution yesterday, so
consistency in the runs leads to more confidence that this will
occur. This track has the potential to bring winds and waves to
the southwest coast, so the forecast bears watching for the next
few days to detect any changing trends.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 119 120 130 131 138 139 160 165 178 180.

&&

SYNOPSIS AND MODEL DISCUSSION...KO/EZ
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SA
LONG TERM...LF