Small Craft Advisory 121, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 PM AKST Sat Feb 9 2019

.ANALYSIS AND UPPER LEVELS...
The amplified upper level ridge that had been sitting over the
Gulf and Southcentral is starting to move slowly eastward as a
trough, associated with a vertically stacked low in the Bering, is
moving eastward. Its frontal boundary stretches from the northern
Bering down across the Pribilofs to south of the central
Aleutians. Gusty winds and primarily rain have been associated
with this front as it progresses eastward towards the southwest
coast and AKPEN throughout the day. Meanwhile, the the AKPEN to
Southcentral continue to sit of the western side of the ridge.
These areas are seeing cloudy conditions, with a few rain showers,
across the region as moisture is being pulled in from the North
Pacific.

&&

.MODEL DISCUSSION...
The biggest item to note for the models in the short term is how
the models are in their second cycle of all of them moving the
low in the Gulf on a farther south trajectory on Sunday. This is
lowering the chances of precipitation around Southcentral Alaska
with the new track.

Models are in good agreement with the synoptic placement and
intensity with the low moving across the Bering through Mon
afternoon.

&&

.AVIATION...
PANC...The possibility of stratus and/or fog continues to be the
concern around PANC. Due to the higher clouds overhead and the
stratus that developed during the morning, it looks more likely
for stratus to be the prevalent condition with fog being less
likely. MVFR ceilings are likely through the night into Sunday
morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Ridging that has been over the area will start to push off to the
east tonight ahead of a shortwave moving in from the west. This
shortwave will meet with another shortwave approaching from the
south and spin up a low in the Gulf Sunday morning. This new low
will bring precipitation to Kodiak Island and the eastern Kenai
Peninsula, with other locations only seeing occasional light
showers. The majority of the precipitation will be rain with
higher elevations and interior locations seeing snow. The low
will then quickly move off to the southeast with more ridging
building in over Southcentral Alaska on Monday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Saturday
night through Tuesday)...

Two lows will impact the southwest coast over the next three
days. The first low is currently moving through the Aleutian
Islands and will impact the southwest coast tonight into
tomorrow. This low is the weaker of the two lows. It is
anticipated to bring rain and/or snow depending on temperatures at
your specific location in southwest Alaska, so be sure to check
out your local forecast. Also expected are gale force winds,
mainly in coastal areas around Bristol Bay.

The second low is a much stronger low that will move through the
central Bering. Due to its large size and strength, it will have
multiple impacts on southwest Alaska. The first and likely most
significant impact will be sustained gale force winds along
coastal areas of southwest Alaska. Before winds reach shore, a
front dropping fresh snow will (along with recently fallen snow
from the first low) will leave a loose snow pack to allow for
blowing snow to be an issue with these winds. As of now we are not
expecting visibility to reduce below a half mile due to warm
temperatures and and southerly winds, which have a tendency to not
produce intense blowing snow. However, this bears close watching.

The second issue also pertains to winds, which is coastal flooding.
A southwest south to southwest fetch of strong winds has the
potential to create a coastal flood issue for the Kuskokwim and
Delta and Bristol Bay. However, taking a look at today the current
thinking (after discussing with the ice forecaster) is that
shorefast ice will hold and protect the coast. This will mitigate
impacts in the Kuskokwim Delta, which will be the most exposed in
this wind direction. The Bristol Bay area will not see enough of
a fetch for long enough to be an issue. Therefore, not expecting
coastal flooding at this time. We will take another look though.

Lastly, freezing rain could be present as this system will be
sending warm air into southwest Alaska. Looking at forecast
soundings and temperatures today, it does not favor freezing rain.
Therefore, backed off on the freezing rain forecast to a chance
but did not discount it completely based on one model run.

All in all, a busy few days of forecasting for southwest Alaska.

&&

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

The first of two low pressure systems for the Being Sea is
currently pushing through the central and eastern Aleutians. It is
still forecast to bring gale force winds the Aleutians and Eastern
Bering as it moves east tonight into tomorrow.

The more significant low is still anticipated to enter the
western Aleutians tomorrow night. Forecasts are still going for
this to be a deep and strong low, with a tight pressure gradient.
Therefore, were are still expecting storm force sustained winds
with hurricane force gusts for the western Aleutians and Bering
tomorrow night into Monday. Seas will be correspondingly high with
this low...with wave heights over 40 feet.

The low holds together well as it tracks northeast through the
Bering Monday into Tuesday, maintaining storm force strength over
the central Bering while sending strong gales into the Pribilofs.
The storm will largely exit our forecast area midday Tuesday.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

There are a few systems to watch across the marine areas that have
the potential to produce areas of gales and storms through this
time frame. Starting Tuesday, we'll be monitoring a low departing
through the Bering Strait Monday night that is forecast to
produce storm force westerly winds Monday night, diminishing to
gales across the northern Bering by Tuesday morning. Depending on
the amount of sea ice near the coast, erosion may be a concern.
Confidence is moderate to high with this as model consistency has
been good.

Gale-force westerly gap winds through the Barren Islands out into
the central Gulf are expected starting late Monday night and
persisting almost nonstop through Tuesday. Any diminishing in
those winds will be brief as a strong low moves across the far
southern Gulf on Wednesday. This will turn the winds out of the
northwest as they intensify back to gales over much of the open
waters of the Gulf into Thursday. Confidence continues to improve
for this scenario as well. There is some potential for storms,
particularly in the windier gaps, especially on the north side of
Afognak Island and the south side of Kodiak Island. The winds will
diminish over the Gulf during the day Thursday.

A strong front will move into the far western Aleutians Tuesday
night, but will weaken as it crosses the Bering and reaches the
coast around Nunivak Island and the Kuskokwim Delta around
Thursday morning. Timing with this feature is also well agreed
upon in the long-range models. It's becoming increasingly likely
that storm force southeasterly winds associated with the front
will impact the western Aleutians Tuesday night into Wednesday,
then weaken to gale force when it reaches the Pribilofs and the
Eastern Aleutians by Wednesday night. Southwesterly gales behind
the front are also expected for the Western Aleutians Wednesday
and Wednesday night as the parent low tracks well north and west
along the Kamchatka Peninsula.

&&

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

The long-term forecast pattern, generally well agreed upon in the
models will feature a weakening front moving over southern
mainland Alaska Tuesday and Tuesday night causing mostly mountain
snow showers with no one particular area expected to see much in
the way of precipitation activity. Behind that, a seasonably cold
air mass will move into Southwest Alaska early on Tuesday and
spread across Southcentral by Tuesday night. This cold, dry air
will increase the strong westerly gap winds through the Barren
Islands, Passage Canal, and northerly offshore winds through the
Copper River Delta, Resurrection Bay and possibly Valdez marine
areas. Other than those windy conditions, a period of calm, quiet
weather is expected and the air mass should be dry enough that
areas of fog should be few and far between. A dying front will
approach the coast of Southwest Alaska Thursday evening, but
should dissipate entirely before making any more progress inland
than that. The cold air mass across inland areas of Alaska appears
likely to persist through Saturday, which will also keep the gap
winds going much of that time, especially in those areas with
openings to the Copper River Basin.

Elsewhere, the storm track for much of the long-term will remain
across the western and northern Bering, as strong lows move across
or near the Western Aleutians about once every 36-48 hours. The
first low moves well west of Shemya Wednesday morning, a second
low moves north over the Central Aleutians Thursday night, and a
third low impacts the western Aleutians Saturday night. Each of
these will have gales and potentially storms with them, along with
heavy rains. By Saturday, the models are having their usual
struggles by day 7, but all suggest another dying front will make
somewhat better progress than its predecessors at spreading
precipitation across Southwest Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storms 132 150 175 177 178 352 411 413. Gales 130 131 155
160 165 170-174 176 179-181 185 412 414.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...JW