Small Craft Advisory 699, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 PM AKDT Wed Sep 12 2018

.ANALYSIS AND UPPER LEVELS...
The strong upper level Omega blocking pattern continues with a
ridge across the Alaska Peninsula/eastern Bering Sea with
flanking lows either side (southwest and southeast). Widespread
low stratus and fog, under strong subsidence, continues over the
Kuskokwim Delta, Alaska Peninsula, and eastern Bering Sea. Cloudy
conditions with areas of rain, associated with a frontal system,
is evident over the central and western Aleutians. A fairly
pronounced area of instability has given rise to isolated to
scattered thunderstorms over the central Aleutians. Some cirrus
sliding south along the forward side of the ridge is bringing
some cloud cover. However, unseasonably warm temperatures are
developing across portions of Southcentral, especially in areas
with outflow conditions across the eastern Kenai and northern
Gulf.

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.MODEL DISCUSSION...
Models are in good agreement through the short-term.

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.AVIATION...
PANC...VFR conditions and light winds will persist.

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.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The above normal temperatures will continue across Southcentral
Alaska as ridge remains steadfast. The ridging will inch its way
eastward resulting in widespread subsidence and more northerly
flow aloft. Expect more dry conditions through Friday. Friday
night a shortwave will approach Kodiak from the southwest
bringing low clouds and a chance for rain to the island. The last
time Anchorage had a dry streak from August 27-Sept 12th was in
1984. The past couple of days multiple records have been broken,
primarily along coastal locations which have been experiencing
gusty offshore winds. Seward reached 75F again today which makes
back to back 75Fs at Seward in September which is no small feat.
The last time this occurred in Seward was 1910.

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.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
(Tonight through Saturday)
Warm and dry conditions will continue for another 24 hours. Some
fog will likely form across portions of the Kuskokwim Delta and
near the Bristol Bay coast. A warm front will push across the
AKPEN Thursday morning, before occluding and then weakening near
the Kuskokwim Mountains Thursday evening. A secondary front
(likely a surface trough) will push across the AKPEN early Friday
morning, reaching the southwest coast by evening. Yet a third
surface front will reach the AKPEN early Saturday morning,
reaching the southwest mainland during the afternoon. Each of
these fronts will be accompanied by an increase in showers.

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.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
(Tonight through Saturday)
An unsettled period will persist through the start of the weekend,
as a series of storms and their associated fronts push across the
region. The first area of low pressure will cross the western
Aleutians into the Bering tonight, sending it's warm front
northward. Its associated cold front will begin to sweep from the
western portions of the chain tonight, to the AKPEN by Thursday
morning. A surge of tropical moisture is already encompassing much
of this region, while it sits under an upper-level trough. This
has proven instrumental in a fairly robust lightning output this
morning, and it has continued through this evening with some
decrease in coverage. As such, thunderstorms were added to much
of the Bering and Aleutians to account for this.

For your Thursday, as the first storm continues to push north, a
second low will approach from south to southeast of Shemya,
sending another pair of fronts northward and eastward. This will
keep enough instability for a continued thunder mention, as this
system will also have a tropical connection. By Friday evening,
the system will occlude and fill over the northern Bering, keeping
much of the region in a broad cyclonic flow with showers persisting.
Winds and waves will remain at small craft criteria conditions or
less through the period.

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.LONG TERM FORECAST (Days 3 through 7)...
Long-term models continue to gradually converge on a common
solution for the breakdown of the blocking ridge and accompanying
return of cloudy, rainy, and cooler conditions for Southwest and
Southcentral Alaska. The timing of large scale features in the
most recent model runs is remarkably similar. Over the weekend,
a short-wave moving up the west side of the ridge will push into
the interior, with some showers making it into the area, over the
top of the ridge. Models indicate enough weakness in the ridge by
this point in time to allow the front to cross Southwest Alaska
Friday night through Saturday, bringing rain and cooler conditions.
However, as it tries to cross Southcentral Saturday through
Sunday it will encounter some remnant of the upper level ridge. So
at a minimum, the front will continue to weaken as it arrives in
Southcentral. Certainly expect cloudier and cooler conditions as
we head through the weekend, but rain chances are much more
uncertain. Do not expect a washout by any means; rainfall will
likely be light and focused along and near the mountains.
Meanwhile, the Bering Sea and Aleutians can expect wet and windy
conditions as a series of fairly fast moving storm systems cross
the region.

The next storm system tracking north near the Kamchatka peninsula
will send a front through the western Aleutians and Bering by
Wednesday morning, weakening as it tracks eastward through the
remainder of the Aleutians and Bering. A secondary system will
cross the central Aleutians from the north Pacific late Thursday
night, and strengthen as it tracks into the eastern Bering by
Friday morning.

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

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...PS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...TP/SEB