Small Craft Advisory 664, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
524 PM AKDT Mon Aug 27 2018

.ANALYSIS AND UPPER LEVELS...
Sunday's rainfall produced quick rises on the Little Susitna river
and area streams overnight. As much as 2.6 inches of rainfall fell
near near Hatcher Pass. River levels are already trending down,
but higher levels should be expected in the short term.

The back edge of this weather maker shows up as showers, which are
still spotted on radar this afternoon. These continue along
coastal regions in Southcentral as a low near Prince William
Sound passes through the Gulf of Alaska. Gusty conditions that
were felt around Anchorage and surrounding areas have started to
calm down since this morning.

Ridging behind this front brought drier conditions this afternoon
for much of southwest Alaska and the Aleutians. A North Pacific
low south of Adak will be the next system impacting the western
and central Aleutians and Bering. Stratus and fog are found in
most locations as usual.

&&

.MODEL DISCUSSION...
Models seem to be in better agreement with the placement and
strength of the North Pacific low as it moves into Bering through
Wed night. The NAM was the preferred model due to the higher
resolution, especially for gap winds tomorrow extending from the
Barren Islands to Valdez.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Patchy fog
will develop the vicinity is expected overnight and into early
morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
(Tonight through Thursday)

The forecast dilemmas tonight are how far north will the rain
shield spread that's associated with a Gulf low, and any potential
fog development tonight and tomorrow night for parts of the
area, and winds overnight and tomorrow for some area waters. As
for the rainfall, a low currently south of Seward will continue to
trek off to the northeast this evening before turning east and
roughly paralleling the coast. The models did try to push the rain
shield northward towards the Anchorage Bowl. However, radar
imagery shows this storm maintaining more of an northeast track,
with the rain shield having really slowed down its northward
progression of the deformation rainfall. Thus, the rain looks to
affect mainly the Prince William Sound region and northern Gulf.

As this system departs the region offshore flow and dry advection
should lead to some breaks developing in the cloud cover tonight.
This, combined with saturated soils and light winds may allow some
patchy fog to develop near the Cook Inlet and across the Mat-Su
Valleys both tonight and tomorrow night. With offshore flow in
place and a tight pressure gradient still in place along the Kenai
Peninsula, look for winds to increase to small craft conditions
for Resurrection Bay and Passage Canal, in addition to the coastal
waters. Otherwise, the general theme is for drier conditions and
a return of some sunshine to take hold for Tuesday, before more
clouds roll back in for your Wednesday, ahead of the next system
to affect the region.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper level ridge will build in from the west tonight bringing
drier conditions to the region. However, with abundant low level
moisture already in place, the sinking air with the ridge will
help reinforce low level clouds and lead to development of areas
of fog. Fairly robust northerly flow on the east side of the
surface ridge will lead to locally clearer skies and warmer
temperatures in portions of Bristol Bay, especially during the day
Tuesday. The next storm will arrive Wednesday as a low tracks to
the northern Bering Sea, pushing a warm front northeastward to
Southwest Alaska. With the bulk of dynamics with this system
driving northward to the northern Bering Sea, Southwest Alaska
will see just a glancing blow of rain and winds Wednesday through
Wednesday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The ridge sitting over the Bering Sea will quickly give way to a
series of storms. The first one will lift northward across the
Aleutians tonight through Tuesday, advecting warm and moist tropical
air northward into the southern Bering Sea. A second, trailing
storm will merge with the first storm late Tuesday and deepen as
it continues northward across the Bering Sea. The strongest winds
and heaviest rain with these systems will be right across the
central Aleutians and Bering Sea. As the low tracks northward on
Wednesday a cold front will sweep from west to east across the
Aleutians and southern Bering Sea. This will help improve ceilings
and visibility as the atmosphere destabilizes and lead to gusty
winds.

&&

.LONG TERM FORECAST (Days 3 through 7: Thursday through
Monday)...

Thursday will start out with an area of precipitation associated
with a front north of the area over Interior Alaska. This will
cause broad westerly winds across the area that are likely to keep
any associated precipitation to the mountains over Southern
Alaska. An area of low pressure located west of Nunivak Island
Thursday morning will track southeastward along the Bering Coast
through the day Thursday into Thursday night. This will keep
unsettled weather ongoing along the coast, while much of the rest
of the moisture associated with the front continues eastward into
the Copper River Basin by Friday morning. The low will cross the
Alaska Peninsula during the day Friday and weaken into a surface
trough by Friday evening.

As the trough continues southeastward into the Gulf of Alaska and
away from mainland Alaska, an expansive area of high pressure out
over the Bering will build in for the weekend and into Monday.
This should allow much of Southern Alaska to get a welcome break
from all of the wet weather. While this will be the case for most
of the area there are a couple of exceptions: First, on Saturday
afternoon and evening, a weak cold front will track southward out
of Interior Alaska and into the Copper River Basin. This could
mean a brief period of rainfall for portions of that area Saturday
evening. The models differ on whether or not any rainfall is
produced by this feature at all. Without any moisture source, that
fact is certainly not surprising. The other exception will be the
end of the dry weather as a strong cold front moves into the far
western Bering on Sunday, and reaches the Kuskokwim Delta as early
as Monday evening. Unsurprisingly, there are differences in
timing. Everywhere else, a dry weekend with seasonable
temperatures is expected. Enjoy!

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

SYNOPSIS AND MODEL DISCUSSION...AH/DS
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB
LONG TERM...JW