Small Craft Advisory 980, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 AM AKST Fri Dec 22 2017

.ANALYSIS AND UPPER LEVELS...
The flow pattern aloft is looking both more coherent and
disorganized at the same time. From a broader viewpoint, a much
more coherent trough/ridge pattern is in place with a stout ridge
over the northeast Pacific and weaker troughing from the western
Bering southeastward into the northern Pacific. The disorganized
part is the flow between these two features. There are a number of
disturbances within the flow, each becoming harder to track as it
deamplifies and moves northwestward. Currently there are three
main shortwaves visible on water vapor imagery this morning.

From a sensible weather perspective, an expansive cloud shield
covers an area from Kodiak Island northwestward through the
Arctic. At the surface widespread gale-force winds with an area
of embedded storm-force winds stretches from the Gulf of Alaska
into Bristol Bay. The strong winds are keeping most of the
moisture from reaching the ground in the lee of the mountains,
but some rain and snow is reaching the ground along the Kuskokwim
Delta coast and upslope areas of Greater Bristol Bay. Further
east, light northerly winds for most of Southcentral Alaska with
a steady stream of high clouds. The front lies stretched out from
east to west near Kodiak Island. A stratus deck is entrenched in
the Copper River Basin.

&&

.MODEL DISCUSSION...
Guidance is currently handling the phase of the north Pacific
upper low into the Bering trough much better than previous days,
much less spread among the solutions.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. While a
Turnagain Arm wind exists, as well as cross-barrier southeast
flow, the strong down-Inlet gradient should pull this wind away
from the higher elevations of Anchorage. Thus, wind shear has
been pulled from the TAF at this time.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A gale to storm force warm front will very slowly lift northward
across the Gulf and Kodiak Island the next couple days. With
strong ridging from Southeast Alaska to the eastern Mainland,
lows tracking up from the northeast Pacific are being forced
northwestward to the eastern Bering Sea. Thus, there is very
little northward push behind the front. The latest forecast has
been adjusted to slow the northward progression of winds and
precipitation out ahead of the front, but it may yet be even
slower.

Kodiak Island will remain under the fire hose of moisture until
about midday Saturday, so they remain on track to see up to
several inches of rain, highest amounts on the east side of the
island. The remainder of Southcentral will stay dry, with quite
variable temperatures depending on whether the wind is blowing.
When precipitation finally reaches the Kenai Peninsula Saturday
night and Sunday, the surface front will be in the form of a
warm occlusion. Temperatures will remain cold enough to produce
snow in most places, with rain in the Homer/Kachemak Bay area.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Cloudy skies, warm temperatures, and gusty southeasterly winds
will continue to dominate the weather over the region into the
weekend. This will occur as a series of North Pacific lows move
towards the AK pen, leaving the area under the southerly jet
from a broad trough over the Bering. The first of these lows is
expected to bring high winds to much of Bristol Bay today,
especially to areas along the Aleutian Range and Western Capes
that have seen gusts up to 80 mph already early this morning. The
warm air advection from this low has already brought temperatures
well above freezing to all areas outside of the Kuskokwim River
Valley, however with strong downsloping from the Aleutian Range
and Kilbuck Mountains very little in the way of rainfall is
expected to reach ground in the lower elevations. A second low on
Saturday is expected to take a more southerly track and generally
remain south of the chain. This will prevent another round of high
winds from developing in Bristol Bay, however generally cloudy
and gusty conditions will continue through Saturday with continued
downsloping for most areas. Precipitation may move back into the
area on Sunday as the Saturday low dissipates in the Gulf,
however this shouldn't amount to much more than a few showers
with temperatures slowly falling back below freezing.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
A persistent southerly jet over the Eastern Bering will bring
continued active weather from the Pribilof Islands eastward into
Saturday. The first low currently tracking into the Eastern Bering
from the AKpen will bring gale force winds and rain to the
Eastern Aleutians/Bering today, followed by much cooler air and
northwesterly flow on Saturday. This will occur as a second low
tracks south of the chain, allowing the much cooler air currently
over the Western Bering to spread eastward into the Eastern
Aleutians/AK pen. As as already been observed over the Western
Aleutians, this should provide enough cold air to bring snow to
sea level with gusty northwesterly winds. Some localized areas of
blowing snow may develop on Saturday-Sunday at this occurs,
however with light accumulations expected and ocean temperatures
still around 40 degrees F these are not expected to be too
widespread or cause significant reductions in visibilities.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long-term forecast beginning Saturday evening will start off
with ongoing wet and windy conditions stretching from the northern
Gulf area through the southwest Mainland, and into the
eastern/central Aleutians and Bering as a north Pacific low
begins to track into the Alaska Peninsula. There remains some
model differences regarding the timing of the frontal winds and
precipitation, and how far the system will push into the northern
Gulf coast and Cook Inlet region by Sunday. Currently the middle
ground GFS solution was preferred, bringing the rain over Kodiak
Island northward into the Kenai Peninsula by Saturday evening,
then into the northern Gulf coast by Sunday morning. The low then
begins to track north along the western coast Sunday afternoon,
switching the southeasterly flow over the southern Mainland to
southwesterly flow, which will bring colder onshore flow and
showery conditions over the southwest mainland Sunday night into
Monday morning. This will also bring a slight chance of some
light snow to fall over the Cook Inlet region overnight Sunday
into Monday morning.

On the western periphery of this low pressure system, some strong
cold air advection will persist over the Pribilofs and Eastern
Aleutians through the weekend and into the early part of next
week. This will likely bring snow showers and the potential for
blowing snow over these areas Saturday evening through Sunday
morning. A ridge will build in over the western Aleutians/Bering
Monday morning, and quickly push eastward over the central
Bering/Aleutians by the middle of the week. This ridge will be
short lived as the next trough moves over the area Tuesday. This
system could bring another round of wet and windy weather to the
western and central Bering/Aleutians Tuesday afternoon through
the later part of the week. However, previous runs have shown
significantly different solutions, so confidence in the forecast
from Monday through the end of next week remains low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 161.
MARINE...Storm Warning 130 131 155 160 172 180 181.
 Gale Warning 119 120 127 132 136 137 138 139 150 165 170 171 173
              174 175 178 179 185.

&&

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...PEPE