Small Craft Advisory 597, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 PM AKDT Fri Aug 3 2018

.ANALYSIS AND UPPER LEVELS...

A large upper level and fairly strong surface low center are
moving slowly south across the Gulf. The associated front extends
from the northern Gulf to over the southeastern Gulf this
afternoon. Satellite imagery indicated an open wave traveling
northwest along the frontal boundary in the northern Gulf. Fairly
steady rain continued along the Gulf coast. East to north gale
force winds, associated with the Gulf low, were evident over the
northern and western Gulf. A deformation zone over the Copper
River Basin supported cloudy conditions and light rainfall over
that region. Upper ridging was building east across western
Alaska. Abundant low level moisture and subsidence with the ridge
brought widespread low ceilings and some fog to much of the
Delta/eastern Bering Sea. A frontal trough brought near gale force
southerly winds to the western Aleutians earlier today.

&&

.MODEL DISCUSSION...

Models through Sunday are in fair agreement through Sunday
afternoon. Significant model differences develop Sunday night and
Monday with the timing and placement of precipitation and
pressure centers. That said, it looks to be on the wet side
during the latter side of the weekend into early next week.

&&

.AVIATION...
PANC...VFR and light winds through tonight. IFR ceiling and/or
visibilities are possible Saturday morning but the dry northwest
surface flow very well may keep this from happening, so am keeping
conditions VFR in the TAF. Gusty southeast winds will likely
develop over the airport complex late Saturday afternoon/early
evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Today through Sunday)...

Rain continues overnight across the Copper River Basin as the
frontal boundary remains stretched north from low pressure over
the central Gulf. This boundary diminishes by late Saturday
morning with the system exiting southeast. Partial clearing
overnight along Cook Inlet and northward may allow patchy fog to
develop as winds go light toward early morning.

Another warm day is on tap for Saturday with temperatures climbing
to 70 degrees or just above in many locations. Scattered showers
will develop during peak heating, mainly along the mountain
ranges. Isolated thunderstorms are possible across the Talkeetna
Mountains and Alaska Range due to a shortwave which moves through
zonal flow aloft late in the day.

Winds are expected to increase on Sunday as the pressure gradient
tightens across Southcentral between low pressure tracking across
the interior and ridging centering over the Gulf. This low
pressure system will bring scattered to numerous showers Sunday
afternoon and evening as it moves swiftly east. Gusty winds
through channeled terrain should lighten on Monday as a the
surface low continues on an eastward track into Canada. However,
westerly flow increases across the western Gulf Monday afternoon
with the next low racing across from the Bering. This low pushes
the next front which is progged to bring another round of wetting
rains during the beginning of the next work week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Northerly flow in the boundary layer will persist tonight.
Isolated showers are possible for tonight for portions of
Southwest. There is another storm brewing in the Bering. Expect
this system to glide over the ridge that is over the Aleutians,
and move into western Alaska Saturday evening and Sunday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The longwave pattern features an upper low near Kodiak, a ridge
axis over the Central Aleutians, and another closed low near
Kamchatka. A tight pressure gradient has developed near the AKPEN
and Eastern Aleutians resulting in gusty winds. A surface low in
the western Bering will continue to follow the path of least
resistance and track north and later northeast. The latest runs
of the models show gale force potential with this system. Last
but not least, there is a dome of high pressure south of the Chain
with the ridge axis between Adak and Unalaska. The ridge axis
will slant a little towards the east as the aforementioned low
pressure system moves towards St Matthew Island, but the high
isn't going to move much this forecast period. Stratus and fog
will continue to be a forecast challenge.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...

The models in the long-term continue to show a lot of
discrepancies, but some broad features are coming together. On
Tuesday, the models are in somewhat better agreement. A longwave
trough with embedded shortwaves will swing eastward across the
Bering, making it to western Alaska on Tuesday morning. The latest
model runs all generally agree that Tuesday will be a wet day for
nearly all of southern Alaska in that pattern. Within that large-
scale agreement, however, the local scale details are far from
certain. As such, when and how much rain will fall on any given
location Tuesday are details that cannot be said with any
certainty. By Wednesday, even the large-scale pattern becomes
more uncertain as the Canadian model holds the longwave trough
axis over the Kuskokwim Delta, while the GFS and EC both continue
swinging the trough eastward. Going with that latter solution,
portions of Southwest Alaska will dry out Wednesday, while the
trough becomes negatively tilted resulting in another wet day for
essentially all of Southcentral except Kodiak and maybe the Homer
area of the southern Kenai Peninsula.

By Thursday, the broad GFS/EC solution continues to suggest the
trough continuing to swing eastward with the trough axis somewhere
over Southcentral. That pattern would result in a somewhat drier
day, though lots of clouds and showers would persist for much of
the day, particularly through Prince William Sound and the Copper
River Basin. Meanwhile, broad upper-level northwest flow over
Southwest Alaska and Kodiak will make for much drier weather
there, with a good bit of clearing as well for locations away from
the coast. Friday for now should be a generally dry day for most
of the area, depending on the behavior of an upper level low over
northern and/or western Alaska. By Friday evening another low
moves out of the Pacific and into the Bering coast.

&&

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

&&

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