Small Craft Advisory 728, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 AM AKDT TUE SEP 13 2016

.ANALYSIS AND UPPER LEVELS...
An upper level trough currently running north to south from the
Talkeetna mountains to eastern Kenai Peninsula will continue east
through the early morning hours with a band of more organized
showers following it east. Breezy southerly winds up Cook Inlet
and into the Susitna Valley are following the trough east. Over
Southwest Alaska, showers have diminished with the exception of
some scattered mountain showers and more numerous showers along
the Alaska Range as ridging builds along the west coast and the
Alaska Peninsula. Further to the west a frontal system stretches
across the Bering and central Aleutians with the parent low just
south of the far western Aleutians.

&&

.MODEL DISCUSSION...
Models are currently in good synoptic agreement through the mid
term with only minor differences in the track and timing of the
key features. For the western domain the GFS was preferred as a
good middle ground compromise solution for the low tracking east
along the Aleutians. For the eastern domain, the NAM and Canadian
were preferred to trend towards a slower solution with the front
crossing the Gulf Wednesday and Thursday.

&&

.AVIATION...
PANC...Gusty south winds will continue through early this
afternoon before the passage of the trough and a weakening up-
inlet pressure gradient allow winds to diminish and shift to the
southwest. VFR conditions are expected to persist through
Wednesday morning as high pressure builds over the region.

&&

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

As low pressure deamplifies as it moves north and east away from
Southcentral Alaska today, a slightly cooler and much drier regime
will move across much of the region from the south and west. Winds
will generally continue the onshore trend, except for perhaps in
the Prince William Sound region where a weak surface low and
westerly cold advection may allow for some weak outflow winds,
especially at Seward and Whittier. This pattern will be extremely
short-lived before clouds and moisture return in association with
a large Aleutian low moving toward the area. The initial warm
front will bring showers to coastal locations as early as
Wednesday, with the primary front arriving late Wednesday into
Thursday, bringing the next shot of significant rain and some wind
to much of the region, especially along the North Gulf Coast and
Prince William Sound. This next system does not appear to be a
significant wind threat for the Anchorage area, unlike the
previous system.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Tue and Wed)...
Much of the energy and precipitation associated with the
seasonable low pressure system is now moving to the east of the
area. This will allow for a brief drying trend that will last
until the next front starts to make its way in Wed morning. Some
low clouds and patchy fog could hang on through this morning. But
then skies will slowly clear from west to east today as a
shortwave ridge tries to provide some subsidence to the area. As
the next front approaches from the Eastern Bering tonight, expect
winds to switch to an east to southeast direction and increase
towards daybreak Wed. Rain will reach the Alaska Peninsula during
the overnight hours and should track to inland Bristol Bay right
around sunrise. This system will not pack nearly the punch that
the former system did, so winds and precipitation amounts should
be lighter. As the front falls apart over the area into Thu,
expect more showery conditions with winds starting to diminish
some.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Tue and
Wed)...
The low that is currently just south of Shemya is pushing a
massive occlusion through the Central Bering. The low will make a
slow eastward track right along the Aleutian Chain. As it does so,
gale-force southeast to easterly winds will continue along the
occluded front. This sprawling low will dominate the sensible
weather across the entire Bering. Steady rain at Atka will track
with the front into the Cold Bay area by this afternoon. Steady
rain will persist for areas east of the low center, favoring the
Pacific-facing side of the islands. To the west of the low
center, more showery and gusty conditions will develop and persist
into Thu.

&&

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

Beginning the extended period Thursday morning, a large trough
centered over the Aleutian Chain will be in the process of
supporting the eastward progression of a warm front into southern
Alaska. This will spread showers and rain into the region,
although the strength of this front will be rather weak,
especially compared to the strong front which just moved through
Southcentral. The trough will then move east and stall over the
Gulf through the weekend, keeping a continued cloudy and seasonal
pattern in place. In other words, it will feel like a typical
Alaska fall. Impacts are generally expected to be minimal with no
major storms or heavy rain events...with temperatures remaining
near climatology.

Beginning next week, the large scale pattern becomes increasingly
noisy as the models all diverge with respect to the North Pacific
pattern and a trough moving into the Bering from the Kamchatka
Peninsula. All the major models show rather different strengths and
speeds of this trough, so an ensemble approach was favored which
will depict a zonal flow pattern and will keep precipitation
chances inland along with average temperatures for next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None
MARINE...Gale Warning 170 172 173 174 175 176 177 179 185

&&

SYNOPSIS AND MODEL DISCUSSION...JR
AVIATION...CB
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...JA