Small Craft Advisory 54, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
937 PM AKST Wed Jan 16 2019

.ANALYSIS AND UPPER LEVELS...
There is a vertically stacked low centered about 450 miles south
of Kodiak Island. An associated front stretches from the west side
of the low northward through the Alaska Peninsula into Bristol
Bay. Some moisture from this low is also over the central and
western Gulf of Alaska, with some showers along the Gulf coast
from about Cordova westward. There is and upper level ridge over
north central Alaska through the Copper River Basin. An upper
level low is sitting over the northern Yukon Territory. There is a
flat ridge over the central and western Aleutians extending
northward into the southwest Bering Sea. A front associated with a
surface low over the southern Kamchatka Peninsula is moving
eastward towards the western Aleutians and southwest Bering.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement through the short term
portion of the forecast (Friday afternoon). However, some of the
current forecast challenges, including more subtle low level
features such as fog and stratus, are not usually handled very
well by the models. Therefore forecast confidence is near
normal.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. There is a
chance through early this evening of some brief MVFR conditions
in snow showers, however the probability is too low to introduce
into the TAF.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Saturday)...

A bit of weather affecting Southcentral this evening has the
potential to have some minor impacts as it moves across the area.
A weak front moving westward from off the Gulf is moving into the
Kenai Peninsula this afternoon. In addition to some Gulf moisture,
the front is also bringing in warmer air aloft. Temperatures on
the Hillside are in the upper 30s to around 40. With this warm
air and moisture moving over the sub-freezing air mass currently
entrenched over the Anchorage Bowl and lower elevations of the
Kenai Peninsula, the conditions are set up for some very light
freezing rain over the next few hours. Fortunately, with some dry
air remaining aloft and any and all precipitation so far being
very light in intensity, the impacts should be minor. With that
said however, anywhere a period of freezing rain does occur will
have to deal with slick conditions. Commuters and those traveling
across Southcentral this evening should use additional caution
tonight.

The portion of the front affecting Southcentral will dissipate
tonight, with the rest of it continuing into Kodiak Island late
tonight. The rain will continue in Kodiak City into Thursday
morning before ending as the front continues westward. Conditions
turn very quiet for both Friday and Saturday precipitation-wise.
Concerns beyond Thursday will consist of fog development around
Cook Inlet and the Copper River Basin Thursday night into the day
Friday, and a glancing blow from another Arctic air mass
currently over the northern Yukon. Colder temperatures expected
from the Arctic air mass should keep highs in Anchorage in the
teens on Saturday with lows around zero away from the Inlet.

&&

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

A brief break in the weather overnight has given way to a trough
of low pressure moving across the AKPEN from the Gulf of ALaska.
This should warm up the cooler temperatures experienced overnight
in parts of southwest Alaska. This will be the first in a series
of troughs the next couple of days that will bring rain and snow
to southwest Alaska. Rain is expected more on the AKPEN as far
north as Dillingham, with snow in other locations. This
precipitation type profile results from the surface northeasterly
flow that will continue into the weekend. This will keep
temperatures cool enough for snow, despite the attempt at bringing
in some warmer air from the Gulf of Alaska by the low pressure
system. Northeasterly flow will then become predominant on
Friday, drying out much of southwest Alaska. Overall, pretty quiet
weather for southwest Alaska, with no major weather impacts.

&&

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

Generally quiet weather is expected for the rest of the week as
far as things normally go in the Bering Sea and Aleutians. A low
in the north Pacific will continue to send troughs over the
eastern Aleutians into Friday. Meanwhile, northerly flow will
continue for the Central Bering, as an area of high pressure moves
in and creates a bit of a blocking pattern the next few days.
This will sustain strong northerly winds through Friday, with
gale force winds and some channeling through gaps and passes in
the Aleutians Islands. Expect your typical cumulus with snow
showers as well. The front anticipated to push into the western
Aleutians tomorrow night will get hung up on the backside of this
high pressure and largely be stationary through Friday. Saturday
we begin to see a pattern change when the blocking high retreats
to the north and interacts with low pressure in the north Pacific
to create easterly flow across pretty much the entire Bering Sea.

&&

.MARINE (Days 3 through 5...Sat through Mon)...
Confidence has increased in the strength of the easterly winds
over the Western Bering Sat into Sun. This is primarily due to
better agreement on the closed high over the Bering Strait and
some cold air moving in from the Eastern Bering. Thus, have
started to trend winds high bringing them now into the gale force
range. We will monitor this area for the potential for at least
some storm force gusts.

The low that develops late Sun into Mon near the Alaska Peninsula
still has a high amount of uncertainty surrounding it. Most of it
is tied to exactly what happens with the upper level low over the
mainland. So for now, will likely elect to just hold to small
craft winds. The best chance for any gales associated with this
system would be on its southern flank somewhere south of Kodiak
Island late Mon into Tue.

&&

.LONG TERM FORECAST (Days 4 through 7...Sun through Wed)...

The period begins with a dominating upper level Arctic low over
the northern part of the state. As the low deepens and the trough
axis extends over Southwest Alaska, another important feature to
the south comes into view by Mon. A North Pacific low moves into
the southwestern Gulf of Alaska. While all models indicate the
presence of this Arctic low as well as the low in the Gulf,
however model solutions continue to struggle with placement of
the low by Tue. Currently, the EC/Canadian solution places the low
on a track inland through Southcentral thereby introducing warmer
air and moisture, and ultimately warmer temperatures. Conversely,
the GFS places the low track much further east; moving inland
over the Copper River Basin, thereby delaying the warm-up period
over Southcentral for early next week. By the end of the period on
Wed, all model solutions indicate general agreement with the
placement of a North American ridge building over the southern
half of the state. A stretch of warmer weather like this across
Southcentral is fairly typical in January, so much so that it is
actually reflected in the snow depth climatology for Anchorage. It
is usually accompanied by some downsloping winds.

Meanwhile, over the Bering, a closed upper level high continues
to support cold air advection from Siberia through western AK.
This high slowly drifts westward by Tue and allows an upper level
Kamchatka low over the western Aleutians to advance eastward. By
Wed, this low will ultimately reinforce the building North
American ridge by advecting warmer air in from the south.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 155 165 170-172 177 178 414.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...MO/KO