Small Craft Advisory 363, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 PM AKDT Thu May 3 2018

.ANALYSIS AND UPPER LEVELS...
The persistence of the upper-level low in the Bering Sea and its
frequent surface waves remain the focus for Southcentral and
Southwest Alaska this period.

One shortwave is moving over the Northern Gulf this afternoon. A
stronger wave is passing over the Alaska Peninsula heading for the
Western Gulf. This second wave will be the one to watch for the
potential of stronger gusts along the Upper Hillside.

This wave also connects subtropical moisture to the Northern
Gulf Coast. While the weather pattern remains in motion, limiting
the potential for a fall-like atmospheric river event in this
region, it will certainly be wet in most of Prince William Sound.

A special weather statement is posted for these issues.

Looking west to the main driver of the pattern, the surface low
continues to weaken as it moves north over the Kuskokwim Valley.
Low-level turbulence will remain a concern for aviators through
the short-term period while low ceilings will remain a part of the
longer-range forecast into the weekend and next week.

&&

.MODEL DISCUSSION...
Models remain in good agreement with the placement and track of
the low over Southwest Alaska. Upper-level features and timing are
also in good agreement through 48 hours. The next low approaching
the Aleutians into Sunday has some disparity between the major
models with the GFS being the strongest and fastest of the
solutions.

The NAM was the preferred model over Southcentral for wind
details. Southwest and the Bering Sea Coast regions preferred the
GFS.

&&

.AVIATION...
PANC... Regular shifts in winds should be expected in the next 24
hours as the approaching upper-level wave sets up a faster, gusty
Turnagain Arm wind beginning midday Friday. Low-level wind shear
will develop Friday morning before the onset of gusty southeast
winds across the airport complex late Friday afternoon.
Showers will be minimal, with ceilings and visibility holding at
VFR criteria.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The surface front will begin to push further inland this evening,
with the bulk of precipitation remaining along the Gulf coast.
Strong easterly to southeasterly cross-barrier flow will continue
to limit precipitation for the typical downsloped areas on the
lee-side of the Chugach mountains. Winds and rain will briefly
diminish during the overnight hours as the system dissipates, then
pick back up in Friday morning as the stronger system approaches
the area.

A rapidly deepening surface low will cross the Alaska Peninsula
into the southwest Mainland at about 970 mb Friday morning,
increasing the pressure gradient over Southcentral Alaska. This
will cause winds across the area to increase Friday, especially
along the Upper Hillside and through gaps in the terrain such as
Turnagain Arm. This system has a strong tap of subtropical
moisture, which will push into Kodiak Island late tonight, and
then to the Kenai Peninsula Friday morning. The bulk of the
moisture will then slide slowly east, with most of rain falling
from Prince William Sound eastward on Friday night. A fairly
intact front will push through inland portions of Southcentral
Friday afternoon and evening, and most inland locations will see
some precipitation.

&&

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

Low pressure along the eastern Bering pushes the current front
along coastal Bristol Bay through the Kuskokwim this evening. The
next developing surface low just south of the eastern Aleutians
pushes the next front across the Alaska Peninsula tonight. This
low deepens to 970 mb as the upper low advances and it becomes
stacked on a northward track across Bristol Bay waters Friday
afternoon. Gusty North to east winds develop across Bristol Bay
tonight with strong flow continuing through Friday night. Winds
increase across the Kuskokwim Delta and Valley Friday afternoon as
the low center nears the coast.

The storm system slowly fills as it continues north Friday night
through Saturday. Winds taper down in response with a shift to the
south as the low center moves north of the Kuskokwim Saturday
night. Rain will continue through the weekend as waves of energy
rotate around the core of the low; however, precipitation becomes
less organized on Sunday with the storm system nearing the Seward
Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The storms system across the Bering moves east into Friday
pulling much colder air toward the Aleutians. Gale force winds are
expected across the Bering through Friday as the storm system
organizes and becomes a stacked system over Bristol Bay during
the afternoon. Winds taper down Friday night as the storm system
lifts north across the Southwest mainland and weakens. The next
front moves up from the North Pacific and pushes into the western
Aleutians late Sunday.

&&

.LONG TERM FORECAST (Days 3 through 7...Sun through Thu)...
Once the remnants of the slowly moving low through the Southwest
mainland and associated atmospheric river along the Gulf Coast,
the focus for the long term forecast into early next week will
shift to the building ridge in the Yukon Territory. This ridge
will begin to build into the Eastern Mainland on Monday, however
it will struggle to reach as far west as Southcentral as a deep,
broad and nearly stationary trough sets up near the Pribilof
Islands. This setup will act to amplify the upper level pattern,
and leave a majority of the South Mainland under the influence of
a deep southerly jet into the middle of next week. As a result
there doesn't look to be a significant break to the cloudy and
rainy pattern, especially for the Gulf Coast, though temperatures
will begin to closer to normal as freezing levels rise in the
southerly flow. This should at least provide enough warm air to
cause much of the late season snowfall that has occurred recently
in the low elevations to switch over to rain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 152, Flood Watch 155.
MARINE...Gales 130-132 138 150 155 170-174 179-181 185 352 414.

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...DEK