Small Craft Advisory 771, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 AM AKDT Mon Oct 8 2018

.ANALYSIS AND UPPER LEVELS...

The frontal system associated with the vertically stacked low
currently centered over the western Gulf extends across the
Pribilof Islands and eastern Aleutians early this morning while an
upper level ridge is amplifying over Southwest Alaska. The
pressure gradient tightening between the front and ridge is
bringing windy conditions to the eastern Aleutians and Alaska
Peninsula while the building ridge is bringing areas of fog to
Southwest Alaska. Over southcentral Alaska, the combination of
partial clearing due to the exiting trough and the ridge building
to the west are bringing a mix of stratus and patchy fog.

&&

.MODEL DISCUSSION...

Models remain in good general synoptic agreement for the first
half of the week. While there remains some small difference in
the timing and position of the low lifting north to western Gulf
and Alaska Peninsula Tuesday night all are in agreement that this
will be a strong system.

&&

.AVIATION...

PANC...With a mix of stratus and patchy fog around the area
conditions will likely be variable this morning, bouncing between
VFR and MVFR to briefly IFR at times before skies clear out late
morning through this afternoon.

&&

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

A retreating upper wave heads east and will briefly continue a few
showers over the mountains along the Copper River Basin.
Subsidence with a building ridge moving in from the west will
bring stratus and fog this morning to the Cook Inlet Region,
Anchorage Bowl, MAT-SU Valleys, and portions of the Copper River
Basin. These conditions should improve significantly by mid
morning as drier air moves in. The pressure pinch between the
ridge and a eastward retreating low over the Gulf will bring
generally offshore flow with brisk gap winds over the eastern
Kenai Peninsula and North Gulf Coast through early afternoon.

The long wave upper trough digging south across the north Pacific
will be the conduit to pull intensifying surface lows north
tonight through Tuesday night. The first, and weaker of the two
lows, will move to near Kodiak Island tonight then weaken as it
heads up Cook Inlet Tuesday. This low and accompanying front will
bring widespread rain and gales to the the western Gulf tonight
and Tuesday. Rain will generally be confined to east upslope areas
with locations to the lee of the Chugach Mountains generally in
the rain shadow with strong easterly cross-barrier flow.

The second in a series of surface low is the remnants of typhoon Kong-
rey. This low will be the stronger of the two lows and move to
somewhere between the eastern Alaska Peninsula and Kodiak Island
late Tuesday night. Another round of rain and wind (stronger) is
expected with this low. Also expect strong gap winds especially
along Turnagain arm and through Portage Valley. The brunt of the
rain will once again be along the coasts and east upslope areas as
strong cross-barrier (southeast) flow will keep areas to the lee
of the Chugach on the dry side.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
(Today through Tuesday night)

Drying conditions and areas of fog can be expected this morning,
as a transient ridge of high pressure builds across the region.
Some of the fog has already been locally dense, with visibilities
as low as 1/4 of a mile. A few breaks should develop this
afternoon as subsidence associated with the high mixes down,
helping to erode the cloud deck from the top to bottom.

Our attention then turns to a a pair of systems that will cross
southwest Alaska. The first will be an occluded front associated
with a low in the western Bering. This feature looks to reach the
coast and AKPEN Tuesday morning. Widespread rainfall will develop
with this front while spreading northward through the day. Then, a
rapidly deepening area of low pressure will move towards the
AKPEN Tuesday night/Wednesday morning and then ride the spine of
the Alaska range through the day. Widespread rainfall, some of
which will be moderate to locally heavy at times, is expected with
this storm. This is due to a tropical feed of moisture, as it
taps moisture from near Hawaii.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
(Today through Tuesday night)

An area of low pressure will continue to wobble across the
western Bering, with its associated surface front racing eastward
across the eastern half of the area. It should reach the coast of
southwest Alaska by late Tuesday morning. Until then, widespread
rainfall and gale force winds will accompany both the front and
the backside of the low across the western Bering/Aleutians.
Sustained gale force winds and seas of 12 to 16 feet will be
common ahead of the front and near the low.

The next feature of interest will be a rapidly deepening area of
low pressure (the remnants of former Super Typhoon Kong-Rey),
that will approach the AKPEN by Tuesday evening. Widespread
moderate to locally heavy rainfall will develop along and ahead of
this storm. Sustained storm force winds will likely develop east
of the Shumagin Islands with seas of 19 to 24 feet. On the
periphery of this system look for sustain gales and seas of 12 to
18 feet.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The long term, beginning Wednesday night, has a pattern with a low
over the Bering and ridging east of the Gulf. This setup will last
through the rest of the week and will result in multiple
shortwaves rotating around the Bering low that will swing in over
the southern mainland. More rain is expected with each wave moving
through. This pattern looks as though it could break up over the
weekend but there is a fair amount of model disagreement for this
timeframe. With the wide spread of operational guidance, the
ensembles were preferred.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 119 120 130 131 132 137 138 170 171 172 177
                      178 179 181 185 351 352 414

&&

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...DK