Small Craft Advisory 790, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 AM AKDT SAT OCT 8 2016

.ANALYSIS AND UPPER LEVELS...

The broken record of idyllic autumnal weather continues across
Southcentral Alaska this morning as surface high pressure remains
in place. A well defined center of the surface high is offshore
over the central Gulf, leading to a very light westerly wind along
the coast. Inland, calm winds, even in the Matanuska Valley, are
allowing for widespread 20s from the interior Kenai Peninsula
northward. The cold spot in all of southern Alaska remains
Gulkana, where a reservoir of stratified cold air in the Copper
River Basin being allowed to cool more and more each day with
rapidly lengthening nights.

Conditions are far different over Southwest Alaska, as a strong
front remains nearly stalled along the coast from the north
Pacific through Bristol Bay through the Kuskokwim Delta. The bite
from the front are the winds, as associated precipitation is all
bark. Cape Newenham reported a gust of 72 mph yesterday evening,
with 30-40 mph gusts common through that entire area.
Precipitation is limited to a few isolated showers near the coast.
King Salmon's 00Z sounding shows that the entire atmosphere is
incredibly dry, so any precip that makes it to the ground, if any,
is only amounting to a trace.

A strong low over the Bering is moving northward over the middle
of the Bering Sea. It too has been a big wind maker, causing wind
gusts as high as 75 mph yesterday morning in Atka. The winds have
been steadily increasing over the Pribilofs last night as well as
the low makes its closest approach, with frequent wind gusts over
50 mph at both Sts. George and Paul.

This weather pattern is the direct result of a textbook omega
block over Alaska. An omega block is called that because it
resembles a Greek capital letter omega. Upper level lows over the
Bering and near the southern tip of the Panhandle are separated by
a very amplified upper level ridge centered over the heart of the
state. Thus, the jet stream weaves in between these features,
creating the look of the Greek letter omega. Under the upper level
lows, the weather is active, as evidenced by the current
conditions over the Bering, while the rest of the state is under
the ridge, resulting in calm, quiet weather. The omega block is
called a block because it is a stable weather pattern, meaning it
usually persists for a long time. Thus the forecast remains sunny
and dry over the mainland, while a seemingly endless train of
storm after storm track through the Bering, but have a very hard
time making any eastward progress.

&&

.MODEL DISCUSSION...
Models overall are in fairly good agreement through Sunday
morning with the synoptic features, but begin to struggle by
Sunday afternoon with another North Pacific low tracking into the
Western Aleutians. Models remain in good agreement with the Bering
Sea low tracking back to the Northwest Saturday and into Eastern
Russia by Sunday morning, as well as the timing and strength of
the frontal winds and they push further inland into the Western
Coast.

As mentioned above, the models then begin to struggle with
the timing and placement of the strong winds associated with the
next North Pacific system, but seem to agree on the strength of
the main system. The American models (GFS/NAM) were the preferred
solutions regarding this system, as they show strong gusty winds
pushing into the Central Aleutians Sunday Afternoon. However,
forecast confidence begins to drop off over night Sunday into
Monday, as the models begin to struggle with the potential
development of a triple point low south of Adak Sunday
night/Monday morning. This can directly affect the intensity of
the winds as they begin pushing into the Eastern Aleutians Monday
morning.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The biggest change in forecast thinking is that models are more
aggressive in pushing the ridge over the state eastward which will
allow the front approaching Kodiak Island today to move farther
northeastward tomorrow. This will spread cloud cover and some
precipitation farther up Cook Inlet on Sunday than previously
expected.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Much of the active weather today will be confined to the
southwest coast where a nearly stationary frontal boundary will
bring periods of rain as well as strong SE winds, especially to
the AKpen and Kuskokwim Delta coast. This front will begin to move
inland over Bristol Bay starting this afternoon as a wave begins
to develop over the AKpen, allowing strong winds to spread
northward into the Aleutian Range. This front will also bring
widespread rain to much of Bristol Bay through tonight, which may
be heavy at times near southeast facing terrain (such as northwest
Bristol Bay) due to strong upslope flow. This front will then
continue lifting northwards into the Kuskokwim Valley as it
dissipates, spreading a chance of rain but with diminishing winds
to most the southwest Mainland for the remainder of the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Most of the area will see a short lived period of much quieter
beginning this afternoon as the storm force low over the central
Bering continues to weaken as it moves northward. Yet another
storm force low approaching the central Aleutians on Sunday
afternoon will track further east into the Aleutians as ridging
over the Mainland begins to shift eastward. This will allow strong
winds to reach as far eastward as Dutch Harbor by late Sunday
night before spreading into the Bering for early next week. The
good news is that this system will be slightly weaker than the
remnants of Super Typhoon Chaba which brought a brief period of
high winds to the central Aleutians yesterday. There is however good
agreement that it will bring a broad area of storm force winds and
seas upwards of 20 ft to the central-eastern Aleutians into
Monday.

&&

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

A high latitude omega blocking pattern will continue across the
Bering Sea and Alaska through midweek before the patten finally
breaks down. This will lead to continued sunshine and near normal
temperatures across the Alaska mainland but lead to a wet period
across the Bering Sea and Aleutian Islands. With the ridge portion
of the omega block over the mainland, an amplified trough and
upper level low over the Bering Sea and North Pacific will
continue to bring system after system through the Bering Sea. The
jet stream will become more zonal on Tuesday which will help bring
about the transition that will break down the upper level ridge
over the mainland. Models struggle quite a bit from Tuesday night
onward as the blocking pattern breaks down as the different models
bring about the demise of the upper level ridge over the mainland
in different ways and at different times. However, a potent area
of low pressure is likely to develop over the western Aleutians on
Monday and drift into the North Pacific south of the Alaska
Peninsula Tuesday night. Models have trended further south from
run-to-run as colder air coming off the coast of Russia will
prevent a lot of deamplification of the upper level trough over
the Bering Sea.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...storm 185.
         gale 150 160 165 175 176 177 178 179 180 181.
&&

SYNOPSIS AND MODEL DISCUSSION...JW/TP
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...MC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1225 PM AKDT SAT OCT 8 2016

AKZ121-100345-
WESTERN KENAI PENINSULA-
INCLUDING THE CITIES OF...KENAI...SOLDOTNA...HOMER...
COOPER LANDING
1225 PM AKDT SAT OCT 8 2016

...SKILAK GLACIER-DAMMED LAKE IS RELEASING...

NO FLOODING IS EXPECTED AT THIS TIME.

RESIDENTS ALONG THE KENAI RIVER, PARTICULARLY IN THE KENAI KEYS
AND BIG EDDY AREAS, SHOULD BE AWARE THAT WATER LEVELS WILL BE
RISING OVER THIS WEEKEND INSTEAD OF FOLLOWING THE NORMAL TREND OF
DROPPING BEFORE WINTER. NOW IS THE TIME TO PLAN FOR HIGH WATER AND
TAKE NECESSARY PRECAUTIONS, INCLUDING SECURING EQUIPMENT AND
MOVING ITEMS TO HIGHER GROUND.

KENAI RIVER LEVELS AT THE OUTLET OF SKILAK LAKE HAVE BEEN SHOWING
A SLIGHT INCREASE OVER THE LAST COUPLE OF DAYS WHILE THE UPPER
RIVER AT COOPER LANDING CONTINUES TO STEADILY FALL. BASED ON
CURRENT ESTIMATES OF THE SKILAK GLACIER-DAMMED LAKE VOLUME AND THE
LIKELY RELEASE RATE, PEAK RIVER LEVELS ARE NOT EXPECTED TO RISE
ABOVE FLOOD STAGE AT THE KENAI RIVER GAGE BELOW SKILAK LAKE OR
AREAS DOWNSTREAM.

WATER LEVELS ON SKILAK LAKE AND THE KENAI RIVER DOWNSTREAM FROM
SKILAK LAKE ARE EXPECTED TO CONTINUE SLOWLY RISING THROUGH THIS WEEKEND
WITH PEAK WATER LEVELS ON SKILAK LAKE EXPECTED TO OCCUR ON OR NEAR
TUESDAY OF NEXT WEEK. SKILAK LAKE IS FORECAST TO RISE
APPROXIMATELY 2 TO 3 FEET WITH AREAS DOWNSTREAM ALONG THE KENAI
RIVER EXPECTED TO RISE BETWEEN 1.5 AND 2.5 FEET. IN SOME AREAS
ALONG THE LOWER KENAI RIVER WATER LEVELS MAY APPROACH BANKFULL.

NO SIGNIFICANT PRECIPITATION IS EXPECTED TO COINCIDE WITH THIS
GLACIER-DAMMED LAKE RELEASE EVENT. UNCERTAINTY EXISTS IN THE RATE
THAT THE GLACIER-DAMMED LAKE WILL DRAIN. THIS STATEMENT WILL BE
UPDATED AS NECESSARY IF THE LAKE APPEARS TO BE DRAINING FASTER OR
SLOWER THAN EXPECTED.