Small Craft Advisory 671, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
410 AM AKDT Mon Sep 16 2019

.ANALYSIS AND UPPER LEVELS...

A strong upper level jet remains in place over the AKPEN with a
deep 500 mb low centered over the Gulf. Moderate rain is indicated
on radar along coastal areas of the Kenai and Prince William
Sound on the northern edge of the associated surface low. Showers
are also occurring over the AKPEN behind the low in a
gusty northwesterly flow. Farther west, a ridge is bringing
settled weather to the central Aleutians this morning, while
another strengthening low is leading to rain over the western
Aleutians along its associated warm front.

&&

.MODEL DISCUSSION...

Synoptic models remain is good agreement in the short-term
regarding the brief break in the rain for most areas through
Tuesday and its return on Wednesday. Confidence remains relatively
high.

&&

.AVIATION...

PANC...MVFR ceilings will persist through this early morning as a
low departs to the south. VFR ceilings are expected to persist
thereafter. Winds will remain light through the day.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2/Today
through Tuesday night)...

A gale force low over the northern Gulf will exit southeastward
today, with winds and rain diminishing behind it. While most of
the rain has already ended across Southcentral Alaska, the
atmosphere is still quite moist. As mid and upper level clouds
begin to diminish this morning, areas of low clouds and fog
will settle in. Increasing offshore flow should lead to decreasing
clouds most places this afternoon. The exception will be the
northern Susitna Valley and the Copper River Basin. A digging
arctic trough will track eastward across these areas late this
afternoon through tonight leading to areas of rain. This trough
looks like it will track just far enough south to help strengthen
gap winds along the north Gulf coast and Prince William Sound.
Gusty winds will also linger through tonight across the western
Gulf and Kodiak, where pressure gradients remain tight.

There won't be much of a break before the next storm is upon us.
Tuesday will start out sunny in Southcentral, but rain will reach
Kodiak during the morning hours, then spread to the rest of
Southcentral Alaska Tuesday afternoon through Tuesday night. Each
of these storms has looked just a little bit different. Compared
to the one that moved through Sunday, the upper level flow will be
much more amplified, leading to a stronger and larger storm.
Expect higher rainfall amounts as this moves through Tuesday night
and Wednesday. With the surface low taking a track to Southwest
Alaska, this will also produce stronger southeasterly gap winds,
especially along Turnagain Arm and the Anchorage hillside. This
will not be a downslope situation though, thanks to a strong
southerly jet aloft and a long fetch of tropical moisture
transport.

&&

.FIRE WEATHER...

Conditions will dry out a bit today through Tuesday, though as is
typical for September relative humidities will remain fairly high
for the bulk of each day. Rain will then move back into the region
Tuesday afternoon through Tuesday night. The overall weather pattern,
with widespread wetting rains every 2 days or so, looks like it will
persist for at least the next week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-3: Mon-Wed)...

A few showers remain across the Bristol Bay region spotted on the
King Salmon radar. These showers associated with an upper level
wave will diminish as we head into the afternoon. Dry conditions
will be spotted around the remainder of Southwest Alaska to start
off the week. As a brief period of ridging builds in, the
potential for fog development returns in the overnight hours
along with light winds.

This less active pattern quickly transitions back into a rainy
forecast on Tuesday morning as a new front associated with a
stacked low in the eastern Bering moves inland. The widespread
rain will move eastward across to the Kuskokwim Delta and Alaska
Range through Wednesday afternoon, with the remainder of Southwest
staying under the influence of a showery pattern.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1-2: Mon-Tue)...

Areas south of the Alaska Peninsula will continue to see gale
force winds out of bays and passes, which will diminish as we head
into the afternoon and evening hours.

The attention quickly shifts back to the North Pacific low in
western Bering where this new system is bringing gale force winds
as it crosses the Aleutians lifting into the central Bering for
Tuesday morning. This low will continue to deepen towards 988 mb
as it progresses eastward into the eastern Bering and Southwest
coast by Wednesday. Expect the strong winds and widespread
rainfall to continue with this system.

&&

.MARINE (Days 3 through 5)...

There is high confidence that a low in the eastern Bering early
Wednesday will help to bring gale force winds around the eastern
Aleutians and Alaska Peninsula. As the low moves over mainland
Alaska through the day on Wednesday the winds will diminish. Out
west, there is lower confidence that a North Pacific low
approaching the western Aleutians on Wednesday will bring gale
force winds to the area. These winds are expected to drop to
small craft level on Wednesday. Winds look to stay light Thursday
and Friday.

&&

.LONG TERM FORECAST (Days 3 through 7)...

There is good agreement amongst the models of an unstable pattern
remaining over southern Alaska through the weekend. This would
keep a chance of showers for most locations. However, the
Aleutians and north Gulf coast will see more activity with a
series of lows tracking through the area from west to east while
staying just south of the Aleutians.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 119 130 132 150 172-178 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...DK