Small Craft Advisory 295, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
441 PM AKDT Sun Apr 8 2018

.ANALYSIS AND UPPER LEVELS...
High pressure is continuing to bring generally sunny skies to much
of the Southern Mainland of the state, however this is beginning
to break down as a shortwave trough approaches from the south. So
far the greatest impact from this shortwave has been for some
increasing clouds over the North Gulf Coast, but showers are
beginning to appear over the Central Gulf on Middleton Radar which
will continue tracking towards the coast this evening. This
shortwave is associated with a deeper low currently centered well
south of the Gulf, but is tracking northward will become the focus
for increasing winds and rainfall to the Gulf tomorrow. Over the
Bering Sea, a broad gale-to-storm force low is beginning to enter
the Western Aleutians while its associated gale force front
stretches through the Eastern Aleutians. This system will continue
moving to the east today and begin merging with the Gulf low for
Monday.

&&

.MODEL DISCUSSION...
Model agreement remains generally good through early this week,
with the main differences being how far north the approaching Gulf
low will track. Previous runs had eroded the Mainland ridging too
quickly, bringing it's associated front much further north. With
todays model runs there is now increasing agreement that the
front will remain south of Middleton Island, leaving much of the
impacts from it confined to Kodiak Island and southern portions of
the Kenai Peninsula. As a result winds and POP's were both
increased today for the Gulf/Kodiak Island with warmer/drier
conditions for the Gulf Coast and Southcentral with good confidence.

&&

.AVIATION...
PANC...VFR conditions and light northerly winds are expected to
prevail through Monday afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A low pressure system currently over the Northern Pacific will
push into the Gulf of Alaska overnight. Cloud cover will increase
out ahead of the system over Southcentral keeping overnight lows
at or above the freezing mark for most locations with the
exception of the Susitna Valley and Copper River Basin. A weak
surface trough along the Northern Gulf Coast will bring scattered
showers to sea level locations with some light snow expected in
the coastal mountains overnight. By tomorrow morning, a front
will spread a wide swath of rain across the Southern Gulf into
Kodiak. The low is expected to deepen to sub 970 mb by Tuesday
leading to gale force winds developing over the waters around
Kodiak, especially across the Barren Islands and down through
Shelikof Strait Monday night into Tuesday. The front is expected
to stall some over Kodiak which, combined with strong on-shore
flow, will lead to decent rainfall accumulations over the island,
with 2-3" expected through Tuesday.

High pressure building in over the interior will block the low
from progressing north, keeping precipitation confined to Kodiak,
the Gulf and the Eastern Kenai Peninsula, with dry conditions
expected over the Western Kenai, Anchorage, and the Mat-Su Valley.
Warmer air and slightly clearing skies north of the system will
lead to the warmest temperatures of the year so far, with most
locations north of the Gulf Coast seeing highs in the low to mid
50's on Tuesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The weak ridge over mainland Alaska will provide one more night of
dry and mostly clear conditions across the southwest mainland,
with diminishing offshore flow supporting patchy fog development
across the Kuskokwim Delta. An approaching Bering Sea front will
then bring increasing cloud cover and another chance for
precipitation to the area by Monday afternoon. This front will
begin to stall out and weaken as it reaches the coast, keeping
most of the precipitation potential confined to the immediate
coast and western portions of Greater Bristol Bay. Precipitation
type should be mostly rain as warmer air moves into the region,
however some snow may briefly mix in at the onset of precipitation.
Rain will linger along the coast through Tuesday afternoon as the
front remains just offshore and is temporarily reinforced by a
weak disturbance moving in from the southeast Monday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The deep low currently entering the western Bering and an
associated front tracking east through the Aleutians will bring
active weather to most of the region through the early part of the
work week. The front will quickly track eastward from the Central
Aleutians to the southwest coast by Monday afternoon, bringing
primarily rain and gusty southeast winds to the Pribilofs and
Dutch Harbor overnight and then to the Akpen Monday morning. Some
snow may mix in at the onset of precipitation, however
temperatures should otherwise be warm enough to support rain as
the dominant precipitation type with the passage of the front.
Meanwhile, storm force winds will spread over the Western
Aleutians and surrounding waters this evening and persist through
Monday afternoon as cold air wraps around the back side of the
low. Cold advection will also touch off widespread snow showers
over the western half of the Bering through Monday night on the
southern periphery of the advancing low. Shower activity will
begin to trend downward across the Bering by Tuesday as the low
gradually fills and the front stalls and weakens near the
southwest coast.

&&

.LONG TERM FORECAST (Days 3 through 7)...
On Tuesday night, a strengthening low south of the western
Aleutians will track east centered along 48N. After becoming
vertically stacked south of the central Aleutians on Wednesday,
the low will turn more to the east-southeast Wednesday night and
Thursday before getting pulled into and merged with the broad
upper level low stretched over and to the south of the Gulf
Thursday night and Friday. A large upper level low/trough over
the Kamchatka Peninsula on Friday will track east over the western
Aleutians, Bering and North Pacific Friday night and Saturday,
while a rapidly strengthening North Pacific surface low out ahead
of it lifts north over the western Aleutians and then into the
western Bering.

In response to the deepening western low, upper level ridging
will build over the central Aleutians and Bering on Friday and
then continue amplify as it shifts east over the eastern Bering
and Alaska Peninsula Saturday to become centered over western
Alaska Saturday Night and Sunday. As compared with yesterday's
runs, models are trending towards keeping the axis of the upper
level ridge centered further to the west through the weekend
(centered over western Alaska as opposed to bringing it east to be
centered over all of Mainland Alaska), although significant
uncertainty remains. The challenges for the models include the
handling the cold upper low over the Arctic Ocean and far northern
Canada and the Aleutian/Bering low.

Model runs favoring digging an arctic trough south through
eastern Alaska and northwestern Canada would tend keep the upper
ridge of a higher amplitude and further west, putting Mainland
Alaska under northerly flow aloft and making very dry north to
northeasterly outflow winds a potential concern for southern
Alaska in the Sunday and Monday time period. If the westerly low
turns out to be more dominant and progressive, this would tend to
push the ridge further east bringing a couple of days of warmer
weather to mainland Alaska for the weekend, but opening the
Aleutians, Bering and eventually Southwestern Alaska to more
zonal westerly flow and a more active storm track for the first
half of next week. If both troughs remain equally influential and
end up phasing, the third potential synoptic outcome would be the
suppression of the upper level ridge with temperature holding
closer to or just above climatological normals and a gradual shift
to weaker zonal flow with the jet stream and storm track
remaining well south of the area and aimed at the Pacific
Northwest next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 120 130 131 132 138 173 175 176 185.
		 Storm 177 178.

&&

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...KVP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...JR