Small Craft Advisory 614, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
735 PM AKDT Fri Aug 10 2018

Updated for Long Term Discussion

.ANALYSIS AND UPPER LEVELS...

Low pressure in the eastern Bering Sea continues to push
northeastward extending a front over the eastern Bering Sea and
Alaska Peninsula. Weak support aloft and a loss of organization
aloft has allowed this low to fill and weaken but the front
remains present. Visible satellite imagery shows wide spread
cloud cover over most of southwest Alaska with a dry slot sitting
over the southwestern mainland. Radar returns are showing a swath
of rain over the western coastline stemming from that front.
Ahead of the low, a weak ridging pattern is taking hold over
eastern Alaska bringing clear skies and dry conditions to the
area.

&&

.MODEL DISCUSSION...
Early on, models are in good agreement as the low pressure in the
eastern Bering dissipates. However, cohesiveness is short lived
as the remnants of typhoon Shanshan advances towards the central
Aleutians. There is quite a bit of disagreement both in the
placement of the low but also the speed in which it moves. For the
entirety of the track of this low, the EC is quite a bit faster
with the NAM sitting between the EC and the slowest solution, the
GFS. While the timing differs, the general track of the low is
consistent.

&&

.AVIATION...
PANC...VFR conditions will persist. Light winds will last into the
afternoon before increasing out of a south to southeast direction
as the pressure gradient increases due to the Bering low moving
toward southwest Alaska and ridging along the Gulf coast.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The forecast for this weekend will be the dominated by three
separate weather systems, each progressively stronger than the
last. Presently, a transient ridge is giving way to a shortwave
lifting through the Aleutian chain and into our area. With this,
rain will spread across Southcentral this evening and into the
overnight hours. The Anchorage Bowl can expect to see rain
beginning to fall later this evening and last through the morning
hours. By morning, there will be a 6 to 12 hour break in the rain
before a second weather system moves in on the heels of this first
one. The next weather system can be seen this evening south of
Adak and will lift in a similar manner as tonight's rainmaker.
With more of a tropical connection, heavier rains can be
anticipated to last through late Saturday night.

Attention then shifts towards the third weather system. This
system is from remnants of tropical storm Shanshan as it moves in
from the north Pacific. This low will deepen as it moves across
Bristol Bay and lifts towards Bethel Monday morning. An attendant
warm front will move across Southcentral overnight Sunday,
bringing heavy rains to coastal areas. Anchorage will be rain
shadowed for most of the time, but strong winds are anticipated.
Model guidance has not fully locked onto this post tropical system
with any consistency for the last few days. This has caused
confidence to fall a little for Anchorage, but we are anticipating
winds to increase along Turnagain Arm and the upper hillside
overnight. Some of the winds may get pulled into town for some of
the time, but it is not looking to be as strong as our last spring
time storm. Problems could arise with full foliage and very
saturated soils.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The low centered off the Kuskokwim Delta coast will weaken in
place tonight through Saturday morning while its front sweeps
across southwest Alaska. The flow aloft will be from the southwest
through Saturday evening, keeping conditions moist and showery.
The next system will begin to impact the area Saturday night, as a
very strong low moves into the eastern Bering. Winds and
precipitation will increase on Saturday night and Sunday morning
as the low moves toward the Southwest coast Sunday afternoon. The
front will quickly traverse the area during the day Sunday, and
there will be a slight risk of thunderstorms Sunday afternoon in
the middle Kuskokwim basin.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The main weather threat will be from a strong low moving northeast
into the area Saturday and Sunday. A moisture band from the low
will precede the actual low by quite a bit, as precipitation
reaches the Alaska Peninsula late tonight. The "warm front proper"
will reach the eastern Aleutians and Alaska Peninsula around noon
Saturday, while the Storm Force low is centered south of the
central Aleutians. The low center will then deepen and push
northeast, located near Dutch Harbor late Saturday night. The low
will cross into the eastern bering Sunday morning, reaching the
southwest Alaska coast near Cape Newenham Sunday afternoon.

&&

.LONG TERM FORECAST (Days 3 through 7: Sunday night through
Friday)...
The extended forecast beginning Sunday night remains in an active
wet pattern across the southern mainland and eastern Bering as low
pressure centers over the Kuskokwim. A cloudy pattern with drier
conditions is expected to the west across much of the central and
western Bering as a ridge builds from the North Pacific. Low pressure
over the Southwest fills as it takes a slow southeasterly track
to the Gulf Monday through Thursday. Rain should be considerably
less organized by Tuesday afternoon across the southern mainland
with the low center moving to the northeast Gulf waters.

For Wednesday through Friday, isolated to scattered chances for
rain remain across the region as short waves move about a broad
trough along the mainland. During this timeframe for the Bering,
another storm system is expected to track from west to east. Model
uncertainty increases considerably for the second part of the
week, especially in regards to this next storm system. The main
struggle for models is that a strong short wave dives south across
the eastern Bering on Wednesday and they differ in how they handle
this energy with the approaching storm from the west. A blend of
the operational models and their ensembles brings increasing chances
of rain from west to east across the Bering.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm warning 172.
         Gales 130 150 155 160 165 173 174 179 180 413 414.

&&

SYNOPSIS AND MODEL DISCUSSION...RA
SOUTHCENTRAL ALASKA...SS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
LONG TERM...KH