Small Craft Advisory 471, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 PM AKDT Sat Jun 17 2017

.ANALYSIS AND UPPER LEVELS...

A long wave trough controls the North Pacific and Alaska on
either side of the International Date Line. At least four lows
and their associated shortwaves are managing the local weather
effects. Two of these circulations are taking the lead:
the low over the Chukchi Coast adding a northerly push from the
Arctic to the Yukon-Kuskokwim Delta, and the low over the Western
Gulf of Alaska working to return Pacific influences to
Southcentral... all while attempting to continue a northeasterly
continental flow to Southwest Alaska against the low's flow from
the Chukchi coast.

A shortwave is moving northeast toward the Kenai Peninsula from
the Gulf of Alaska. A less-organized wave is moving off the
Western Alaska Range. And a more sizable vortmax is passing Nome
and moving southeast toward Norton Sound.

Soundings around Southwest and Southcentral Alaska this morning are
considerably more tame today compared to yesterday's convective
signatures. That said, convective indices support a watchful eye
over the Kenai Peninsula where we find a Total Totals bullseye of
56 and CAPE (Convective Available Potential Energy) over 800 J/kg
in and around the Kenai Mountains. Storm motion looks to be
slightly West of North. This means that any storms that develop
have a chance to track toward, and perhaps into, the Anchorage
area. Unless the Turnagain Arm's cold water has the last word, of
course.

At the surface, High pressure sits over the Eastern Gulf of
Alaska. And a trough of low pressure stretches from the Central
Interior to the Yukon Delta.

&&

.MODEL DISCUSSION...

Models are in general agreement today but lose their focus Sunday
handling the placement of the low in the Gulf of Alaska and the
High pressure center over Prince William Sound / Kenai Peninsula.

The GFS was the model of choice across the team today.

&&

.AVIATION...
PANC...VFR conditions will prevail through the period. Winds along
the Turnagain Arm will remain gusty into the early hours of
Sunday. Gusts should subside through the day Sunday with a shift
to a light West wind.

.FIRE WEATHER...
Weaker instability over Southwest Alaska should limit thunderstorm
coverage and strength as compared to Friday. Widely-scattered
storms appear mostly limited to the Kuskokwim Valley this evening.

In Southcentral, a few (isolated) strong storms will be possible.
Initiation near or in the general vicinity of the East Fork fire
should imply the potential for gusty and erratic winds. Any storms
that develop have the potential for periods of heavy rain and
lightning.

Sunday's convective weather appears to be nearly absent, save for
some potential near the Alaska Range or Talkeetnas.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
More stable air is working its way into Southcentral Alaska from
the south. However, enough instability remains for some isolated
thunderstorms this afternoon/evening over much of the area.
Thunderstorms on Sunday and Monday will confined to the mountains
around the Copper River basin and Susitna valley as the stable air
is pushed further inland by increasing southeasterly flow aloft.
Some diurnally enhanced breezes are expected with the southerly
push at the surface. Conditions will be mostly dry on Sunday and
Monday, with a wet weather system approaching from the south and
east late Monday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
The thermal trough along the interior will have less influence
than previous days as low pressure along the Bering Strait and
Alaska Peninsula modify the air mass slightly cooler across the
Southwest. Afternoon and evening showers are expected through the
beginning of the week with a few embedded thunderstorms from the
Kuskokwim Mountains east to the Alaska Range. Weak low pressure
across the Southwest keeps flow generally from the south through
Sunday then becomes north on Monday as ridging moves to the
coast. Fog re-develops each night along the Bering and edges into
the coastal communities by early mornings. Visibility reductions
improve by mid morning with diurnal heating.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Low pressure south of the eastern Aleutians and Alaska Peninsula
tracks east through Sunday night bringing low clouds and a chance
of rain through Tuesday as it stalls in the southern gulf of
Alaska. A ridge centered along the Bering slowly shifts east as
the low exits to the gulf. A stable air mass associated with the
ridge traps cooler moist air near the surface bringing widespread
low clouds and fog Monday and Tuesday. The next front moves into
the western Aleutians Tuesday morning bringing southerly winds and
light rain from a weakly organizing system off of the Kamchatka
Peninsula which pairs with a surface low from the North Pacific.

&&

.LONG TERM FORECAST (Wednesday through Saturday)...

Wednesday starts off the extended forecast with the last gasps from
a system in the Gulf of Alaska. The deformation zone associated with
the system should be bringing widespread rain to the Cook Inlet
region. A narrow ridge aloft builds in as the previous system exits,
and drying trend will emerge through the remainder of the week, and
a transition to more of a diurnal mountain shower pattern. Guidance
wants to bring in a transient shortwave trough in the flow from the
southwest, which would bring a quick shot of rain showers to inland
areas of Southcentral. Toward the weekend, another ridge tries to
build in from the Bering Sea. Expect normal to above normal
temperatures with generally light winds for the extended forecast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...MTL