Small Craft Advisory 567, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 AM AKDT Mon Jul 23 2018

.ANALYSIS AND UPPER LEVELS...
The ridge axis has shifted eastward over Southeast Alaska and the
Yukon Territory. There is a longwave trough extending from the
Bering to the North Pacific/Eastern Gulf Of Alaska with multiple
shortwaves embedded in it. At the surface, there is an occluded
low just southwest of Kodiak and this system has brought cloudy
skies to the Anchorage Metro Area. There is a secondary decaying
low between the Pribilof Islands and the Aleutian Chain. Moisture
has advected into the AKPEN, Southwest and Southcentral. Showers
have been detected on the radars at Bethel, King Salmon and Kenai.
Additionally, this pattern has resulted in gap winds for portions
of the Alaska and Aleutian Ranges. Looking upstream, there is
another low southeast of Kamchatka.

&&

.MODEL DISCUSSION...
The models are in good agreement through 72 hrs with the placement
of the main synoptic features which is reflected at the surface
and at 500 mb. There are minor timing differences with the waves
of precipitation but generally expecting broad and moist southwest
and southerly flow across southcentral.

&&

.AVIATION...
PANC...A cirrus deck and and an alto-cu layer have moved up Cook
Inlet and into the PANC aerodrome. VFR conditions are expected for
the ensuing 30 hr period. But there definitely is moisture
advecting towards PANC.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
While the upper level ridge has shifted eastward into western
Canada, subsidence and anticyclonic flow will persist over the
Copper River Basin the next couple days. This will maintain hot
and dry conditions. Meanwhile, a vertically stacked low over the
Bering Sea will drop south of the Alaska Peninsula on Tuesday,
with a plethora of upper waves rounding the low and crossing the
western Gulf, Kodiak Island and Kenai Peninsula. This will bring
periods of rain to the southern to Eastern Kenai Peninsula and
steady heavier rain to Kodiak Island. The persistent southeast
flow will keep the western Kenai mostly dry, though expect
scattered showers as short-waves move through. Areas north and
east of the Kenai Peninsula will see some mid to high clouds,
but remain dry.

As the upper level low/trough amplify over the north central
Pacific on Wednesday, this will build up the downstream ridge
and lead to strengthening southerly flow from the northeast
Pacific to Southcentral. This will drive short-waves inland
across Southcentral, leading to lowering clouds and increased
chances of showers or rain.

&&

.FIRE WEATHER...
A few different stations in the heart of the Copper River Basin
(near Glennallen) reached red flag criteria yesterday. Today looks
very similar, with high temps just a few degrees cooler (with the
strongest portion of the upper ridge now to the east) and winds a
bit stronger with a more favorable surface ridge location. Thus,
confidence is high that critical fire weather conditions will
once again be met late this afternoon through early evening. On
Tuesday, expect increasing high clouds will be just enough to
produce marginally cooler/moister conditions, but conditions
may come close to red flag criteria once again.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (through Thursday morning)...
The active weather literally revolves around an eastern Bering
Sea stacked low pressure system. The second disturbance rounding
the upper level trough is rolling across the AKpen this morning,
and will continue to spread rain over mainly the Bristol Bay area
this morning. Rain will also spread into the southern Kuskokwim
Valley. The Kuskokwim Delta could see some light rain making it
over the mountains, but will largely remain downsloped and dry.
Behind the upper level disturbance, general easterly flow remains
which will continue to promote upslope precipitation along the
Wood River Mountains, along with several lesser disturbances
within the cyclonic flow aloft. That particular setup will promote
showers through Tuesday evening. Tuesday evening will see some
warmer air poking into the Kuskokwim Valley, which will bring
instability and the chance for thunderstorms from Sleetmute
northward. Yet another trough from the Bering Sea (now North
Pacific) storm, swings overhead on Wednesday. Showers will remain
in the forecast, mainly for Bristol Bay, with another chance for
thunder in the Valley. Expect above average temperatures and light
to moderate easterly winds through the period, with abundant cloud
cover.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The low pressure over the eastern Bering will remain parked over
the area through the period. Widespread rain showers will slowly
taper off today, but linger through Thursday, mainly along the
Alaska Peninsula. A front over the Western Bering will keep rain
over the Western Aleutians/Bering through Wednesday before it
moves away. A very warm air mass will move into the Western Bering
behind this front, beginning today. The air mass will promote
widespread stratus and fog.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The longwave pattern beginning Wednesday is a longwave trough
extending through mainland Alaska and across the Alaska Peninsula
with a low anchoring the trough south of the Alaska Peninsula. On
either side of the trough is ridging with the stronger ridge to
the west. This setup should remain through the end of the week
which would bring southerly flow and rain to the southern
mainland with the majority of the rain along the north Gulf coast.
There is more uncertainty amongst the models heading toward the
weekend, but the general consensus is of a low flattening out the
ridge over the western Aleutians and tracking into the Bering. At
the same time the Alaska Peninsula low would diminish and ridging
over the eastern Gulf would intensify through the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...DK