Small Craft Advisory 626, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 AM AKDT Fri Aug 30 2019

.ANALYSIS AND UPPER LEVELS...
A ridge continues to be the dominant synoptic feature over the
mainland this morning with a low to its west over the Bering. The
one notable difference this morning is a strong disturbance racing
eastward along the base of the trough over the western and central
Aleutians. At the surface...the stable air mass over the mainland
has trapped smoke at the surface around area fires and patchy fog
along the coasts, reducing visibilities once again this morning.

&&

.MODEL DISCUSSION...
Models are in good agreement with the track of the front today
through Saturday...however, there is still some uncertainty on how
much precipitation will fall. Total rainfall was generally
increased with higher confidence since the latest operational models
support this trend. Areas of smoke was decreased near Dillingham
today as mixing along the front improves visibilities from fires
nearby. Areas of smoke across the western Kenai and north, were
extended through later this afternoon since little improvement is
expected until the front lifts inland.

&&

.AVIATION...
PANC...MVFR visibilities and ceilings improve during the
afternoon. Ceilings lower again along the front that moves up
this evening from the Kenai. Winds will vary with weak low
pressure driving the front through Saturday afternoon; however,
brief gusty southeasterly flow is expected for a short time as
the leading frontal boundary pushes through.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A bit of a pattern change is expected this weekend as a couple of
systems bring wind and rain to Southcentral.

The upper long wave trough heads east and phases with a north
moving surface low and front approaching the western Gulf today.
This system brings widespread rain to Kodiak Island today. The
Surface low heads north up Cook Inlet tonight and will spread rain
across the Kenai Peninsula, Anchorage Bowl, the MAT-SU Valleys.
A more western track would tend to favor a little more downslope
drying for the western Interior Kenai Peninsula, however the low
to mid level cross-barrier flow is not overly strong and does
shift around to the south fairly quickly. So overall, most areas
should see a fair amount of rain overnight tonight and morning
hours Saturday. Precipitation should become more showery Saturday
as the upper trough moves north of the Anchorage Bowl by mid-
morning, but will linger as rain over the Susitna Valley into the
afternoon hours. A few lingering showers are possible over the
Southcentral Mainland Sat night.

A strong occluded front, associated with intense low moving near
the eastern Aleutians late Saturday will bring rain to Kodiak
Island Saturday evening and to the Kenai Peninsula/Cook Inlet
Region early Sunday. This system looks to bring a fair amount of
wind with downslope drying the lee (west) of the Kenai, Chugach,
and Talkeetna Mountains Saturday and Sunday with the brunt of the
precipitation falling along the coast and upslope areas over the
Western Cook Inlet/Western Susitna Valley. Strong gap winds
across Turnagain Arm/Portage Valley are expected Late Saturday
night through Sunday.

&&

.FIRE WEATHER...

Western Interior Kenai Peninsula...east winds should be picking up
some with the approach of this first system early this evening.
Still looks like you should get around a .10 inch overnight
tonight. Main concern would be the potential for strong and gusty
east winds Saturday night and Sunday over the Swan Lake fire
area. Cross-barrier flow will likely be strong enough to keep qpf
totals below .10.

Susitna Valley...Should see wetting rains Saturday as the first
system lifts north. The second system on Sunday looks like it will
drop most of the precipitation over the western Susitna Valley
and not much on the fire areas.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

The latest satellite imagery has the remnants of a frontal
boundary from the northern Bering to the Alaska Peninsula and
cloud coverage is impacting much of the region. On the King Salmon
Radar as of 3:12 am AKDT the leading edge of the precipitation
shield is north of Egegik and over Bristol Bay. This system is
past its prime and the front is undergoing frontolysis.
Significant accumulations are not expected with this system and some
locations may only get a trace of moisture or just cloud
coverage. There is a second and more juicy storm brewing on the
horizon. That system will impact southwest Alaska Saturday and
Sunday. High confidence in widespread rains and cooler
temperatures with this system.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

There is a potent low south of the western Aleutians that will
continue to deepen today and into tomorrow. The pressure gradient
will become very impressive with this system. Widespread gales
are forecast and some locations may even experience storm force
winds. This system will push northeast and impact the entire
chain. Rough seas and persistent rain expected with this low.
Sunday the surface low will be northeast of Dutch Harbor. In the
post frontal environment, gusty northerly winds and showers will
linger.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...

Previous Discussion:

The most significant weather feature continues to be the broad
gale force low in the Bering Sea. Little change in the forecast
with this low, as models have been consistent with this system.
This low is still expected to travel northeast through the Bering
Sea, dropping below gale force level Monday evening as it passes
by the Y-K Delta.

A frontal system associated with this low will create small craft
to gale force winds in Shelikof Strait and the Barren Islands
Saturday into Sunday. We did have to increase the wind speeds in
this region as the models were underdoing the winds, but they are
consistent enough that we are confident in the forecast. A barrier
jet will also form in coastal waters near Prince William Sound Monday
as this front impacts the coast, producing some weak gales there.

&&

.LONG TERM FORECAST (Days 4 through 7:Sunday through Thursday)...

Previous Discussion:

Models, while quite sloppy after Monday, are in agreement enough
to still show that we will have a transition to weather more
typical of this time of year. All are showing a more active
weather pattern with at least a couple low pressure systems
entering the Gulf of Alaska, which stem from long wave troughing
that will be in place in the Bering Sea.

Until then, the week will start with a frontal system approaching
the southcentral coast with our first real chance at significant
rain in months. It will also be windy, with a barrier jet setup
along the coast and increased winds down turnagain arm and the
Anchorage Hillside. It should be noted that while many areas
should see rain, it is likely that Anchorage Bowl and the leeside
of the Kenai Mountains (Swan Lake) should see blocking and
downsloping from the mountains. Out in the Bering, the broad slow
will be impacting much of the Aleutian Islands and southwest
Alaska with gale force winds and rain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...DENSE SMOKE ADVISORY 121.
MARINE...Storm Warning 177.
         Gale Warning 130 155 165 170 171 172 173 174 175 176 178 179.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...BB