Small Craft Advisory 277, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
535 PM AKDT Tue Apr 9 2019

.ANALYSIS AND UPPER LEVELS...

A weakening vertically stacked low is spinning over the Gulf of
Alaska at the base of a long-wave trough. This low has very little
upper level support as the jet stream at 30,000 ft is fairly
zonal. The jet is stretched from the western Bering into the
Pacific just south of the Gulf with the highest wind speeds
occurring within the Pacific. At the surface, easterly flow around
the surface low in the Gulf is bringing warm and moist air into
Southcentral and the western Gulf. Convective style rain showers
have been observed by radar throughout the coastal communities
along the northern Gulf, with visible satellite imagery picking up
on cumulus cloud formation along the western Kenai Peninsula. The
next system is quickly approaching as a deep North Pacific low
advances towards the western Aleutians this afternoon. At this
time, a front pushing ahead of this system is just south of the
Aleutian chain.

&&

.MODEL DISCUSSION...
Not a lot to update with the models today as they remain in very
good overall agreement. The largest change of note was reflected
on all the models and has to do with the interaction of the
initial large low and the second triple point low on Wednesday.
The first low, which can be seen on satellite approaching the
Aleutians, will not make much headway into the Bering Sea as the
second low will strengthen quicker and absorb the initial low
Wednesday night. This is a function of the models locking in
better to the jet stream and recognizing the second low will now
be in the correct position to quickly strengthen. This change is
reflected on all four main models. Even after that, the models
remain in good synoptic agreement into the weekend.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. The
southeast winds will likely move in off of Turnagain Arm again
Wednesday afternoon. However, with stronger down-Inlet gradient
expect winds a tad lighter than today, with little or no wind
gusts.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Tuesday
night through Friday)...

Active weather continues for the Gulf of Alaska. The interior
areas of Southcentral are pretty quiet save for some early season
convection producing rain showers. The weak front along the coast
is still sending some showers through the Anchorage area today
and will continue to do so into the evening. Weather should be
steady state for most areas tomorrow, with the exception of
Shelikof Strait and the Barren Islands where easterly gale force
winds will kick up.

The real weather producer is still forecasted to be the low
pressure system moving into the gulf early Thursday. Models have
been consistently indicating a strong low center moving up the
Alaska Peninsula, with fronts from the low pushing north through
the Gulf. Since consistency has been good, we are confident in
the forecast and did not need to make many changes to it today. As
such, we are still anticipating the western gulf to receive gale
to storm force winds on Thursday morning. Winds will then push
north and set up a band of strong winds along the coast. These
winds are forecast to work their way into the Anchorage area,
so a windy day is expected for the Turnagain Arm and Anchorage
hillside. Conditions should calm on Friday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

The showers that have lingered over interior regions of Southwest
the past few days have ended. Attention now turns towards the
potential for fog Wednesday morning. Weak surface flow and
generally clear skies will likely cause low temperatures to fall
to the lower end of model guidance, bringing them closer to the
dewpoint. While winds along the immediate coast will be slightly
stronger as a front approaches from the southwest, confidence is
high that areas of fog will develop, particularly in interior
valleys. This will burn off by late-morning as fair skies are
expected to persist through the day. Temperatures will approach
50, especially in downsloped areas aided by modest ESE flow. Winds
will significantly increase Thursday over the Bristol Bay coast
and the Lake Iliamna area on the northeast side of a strong low,
with gusts of potentially up to 50 mph. Moderate rain should
accompany the winds and will continue through the day as the low
slowly moves across the eastern Aleutians.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

Winds will gradually increase to gales this evening over the
central and eastern Aleutians as a weakening low moves in from the
south. Winds will diminish to sub-gales through the day Wednesday,
with the exception of Bristol Bay and near Saint Matthew Island.
A stronger low will phase with the initial low and likely bring
storm force winds Wednesday evening south of the Shumagin Islands.
Widespread gales will continue south of the Aleutians Thursday as
the low stalls over Bristol Bay. Seas will also build significantly
on the Pacific side of Unalaska and King Cove, potentially reaching
up to 40 ft.

&&

.MARINE (Days 3 through 5/Friday through Sunday)...

...Bering Sea and Aleutian Coastal Waters...
Confidence is high in the pattern, with one large low exiting the
eastern bering Friday and another crossing the Aleutians Saturday
and headed to somewhere in the vicinity of the eastern
Bering/Alaska Peninsula Sunday. There may be some brief periods of
Gales with each of these storms, most likely along the Aleutians
and Alaska Peninsula. However, most of the Bering Sea region
should remain below gale force. Seas will remain elevated south of
the Aleutians/Alaska Peninsula thanks to swell moving up from the
North Pacific, with much lower seas across the Bering Sea.

...Gulf of Alaska...
With the storm track primarily over the Bering Sea and Aleutians,
expect weakening fronts to affect the Gulf. Confidence is fairly
high that winds will remain small craft or lower with each of
these fronts.

&&

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

A front attached to an eastern Bering low will move ashore Friday
afternoon across southcentral and weaken. However, southwest flow
aloft and several disturbances moving across Southwest and
Southcentral Alaska will keep a showery pattern in place for your
Friday. Then, a short-wave ridge will build across the southwest
on Saturday, moving to the Copper River Basin on Sunday. This
will help advect drier air into the region, putting the kibosh on
any precipitation potential (for the most part) with decreasing
clouds expected. Seasonably warm temperatures will continue for
both areas, as afternoon temperatures climb into the mid 40s to
mid 50s, and overnight lows generally in the mid 20s to mid 30s
(coldest for the ridge tops in the Copper River Basin where some
single digit lows are possible).

Further west, an area of low pressure reaches the west central
Aleutians early Saturday, reaching the south central Bering on
Sunday. This system and disturbances aloft in the cyclonic flow
will allow for the wet weather to spread from southwest to
the north and east through the period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 130 131.
         Gale Warning 120 132 136 137 138 141 150 155 160 165
                      170 171 172 173 174 176 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...BB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...PD/SEB