Small Craft Advisory 15, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
519 AM AKST Fri Jan 5 2018

.ANALYSIS AND UPPER LEVELS...
It is a tale of two domains this morning. In the east, high
pressure is building in. This is resulting in offshore gaps winds
in the usual locales (Seward, Whittier, Valdez). It is also making
for a fairly wide swath of fog and low stratus across much of
South Central. This fog shows up very well on POES Satellite
imagery and it is banked up along the Chugach and Kenai Mountains
in addition to filling in many of the valleys of the Kenai
Peninsula. Out west, it is quite a different story. A potent
80 kt finger of the subtropical jet is pushing a strong warm
front through the Eastern Aleutians and the Alaska Peninsula.
Winds along this front are approaching warning-level (75 mph) in
places like Cold Bay, but we expect those strong gusts to be
limited in extent and frequency. Nonetheless, very gusty southeast
winds will continue from the Alaska Peninsula and into SW AK
courtesy of this front. Several other surface low pressure
centers are developing along this boundary. The one that will
eventually emerge as the dominant low into the weekend is over the
west central Bering Sea bringing its own swath of gale-force winds
along with it.

&&

.MODEL DISCUSSION...
Models continue to come into better agreement with the upcoming
pattern. Thus, forecast confidence going into the weekend is
moderate to high. The most challenging part of the forecast is
when the fog and low stratus will ultimately lift around the
Anchorage Bowl and the rest of Southcentral. With an increasing
offshore gradient and drier air moving in, we are still thinking
it will dissipate by later this morning. Otherwise, the only other
significant change to the forecast was to continue to increase
winds and PoPs along the Gulf Coast this weekend. All models
continue to trend a bit stronger with this feature, so we utilized
the GFS to add some more detail. The GFS also came into better
agreement with the other solutions in handling the parent low over
the Bering, so it was used for forecast adjustments out there as
well. Yet another storm-force low will make its way towards the
Aleutians on Sun. While there are some minor differences with this
system, there is a strong general consensus it will bring another
round of wind and rain.

&&

.AVIATION...
PANC...The fog/stratus continues to lurk around the Anchorage
Bowl. As northerly winds continue and usher in drier air, it
should continue to dissipate. However, there is still a fair
chance it could "slosh" off the Chugach and back over the
terminal during the morning hours. Once the fog threat is over,
VFR conditions will persist with light northerly winds.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Upper level high pressure over southern Alaska will slowly drift
north today. Gap winds will decrease today as the associated
surface high weakens. Some fog and low stratus will linger this
morning, then dissipate in the afternoon as the ridge moves away.
A front will move into the southwest Gulf today, with
precipitation and winds reaching southern Kodiak by late morning
and Kodiak City by early afternoon, and then to the north Gulf
Coast tonight. A triple point low will develop along this front
just southeast of Kodiak Island around midnight tonight. This low
will move into the northern Gulf Saturday, setting up south of
Seward Saturday evening and remaining nearly stationary through
Saturday night while slowly weakening.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A potent low is looming down range from Southwest Alaska. A
front will push eastward today with robust southeasterly winds
across the southern Alaska Peninsula. The low has already bottomed
out and the winds for the most part will stay below warning
thresholds, with perhaps just a few isolated peak wind gusts up to
75 mph. The front stalls but will still bring precipitation into
the coastal areas. The biggest impact will be strong
southeasterly winds, particularly in the Bristol Bay area and into
the Kuskokwim Delta. As the forecast period unfolds, the front
will decay and the remnants of the upper trough will lift
northward across Southwest.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A pair of lows will impact the Bering. A 950 mb low north of Adak
will continue to push north and later wobble northwestward and
bring unsettled conditions to the Central and Western Bering. A
second low south near Unalaska will trek northeastward and become
an open wave. The tight pressure gradient will continue to
deliver more gusty conditions today with a peak wind of 64 knots
recorded at Cold Bay early this morning. Expect storm/gale force
winds for much of the Bering into tomorrow. In association with
the aforementioned lows, warm air has advected into the Bering Sea
and multiple locations along the chain will see max temperatures
in the 40s today and tomorrow. Additional shortwave energy will be
ejected from the vortex which will later be in the Western
Bering, bringing a shot of cooler temperatures as the trough
propagates across the Aleutians.

&&

.LONG TERM FORECAST (Days 4 through 7)...
The weather looking into early next week will be dominated by
continued storminess over the Bering Sea/Aleutians with a ridge of
high pressure over the Mainland. The most impactful system in this
period will begin late Sunday with a storm force low that will
move it the Central Bering. This system looks to bring widespread
gales to much of the Bering Sea region to the Southwest coast, but
likely will not move much further inland as high pressure over the
Mainland holds. This should allow for temperatures to remain at or
below normal for most of the Mainland with clear skies through
Tuesday with impacts largely confined to possibility of outflow
winds to the Gulf Coast. This pattern then looks to break down
slightly towards the middle of next week as the high pressure
begins to slide eastward into the Yukon. This would allow
storminess to return to the Southwest Mainland and possibly the
Western Gulf, however confidence in this pattern shift is low as
the models are typically too quick to break down Mainland ridging
in the extended forecast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 150 155 160 165 180 181 185.
 Gale Warning 119 120 127 130 131 132 136 138 139 170 173 174 175
 176 177 178 179.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
LONG TERM...DEK