Small Craft Advisory 290, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKDT Sat Apr 7 2018

.ANALYSIS AND UPPER LEVELS...
Thinning stratus moving off the Chugach Range allowed for a wealth
of midday sun in Southcentral for the start of the first full
weekend of April. A weak lee-side surface trough was making this
possible.

From Kodiak to Unalaska, wraparound moisture from the low in the
Gulf of Alaska kept temperatures in check. Even though the
previous day's front dissipated, a lower cloud deck and rain was
still focused on Kodiak. Rain and snow fell in Unalaska. In
between, onshore flow to the AK Penisula's mountains created a
solid overcast for most, with the exception of Cold Bay which had
some morning sun.

An upper-level low nearing 170W is digging south of 50N helping
to pull in a North Pacific gale-force low along a weakening
occluded front. The front was moving over the Eastern Aleutians.
Another gale-force low is in the southern Bering.

Challenges today, tomorrow, and all of next week will be picking
a winner between incoming solar radiation, albedo, and cloud
cover. Solar influence is growing stronger, but clouds still hold
the trump card.

&&

.MODEL DISCUSSION...
Models were in general agreement today. However, as early as
Tuesday 00z, the ECMWF was showing a tendency toward deeper
pressure centers in the Bering and western Gulf of Alaska.

The team relied on the ECMWF for Southcentral region forecasts,
while the Southwest and Aleutian forecaster worked from the NAM
in the short-term, then blended toward the ECMWF in the mid
range.

&&

.AVIATION...
PANC...VFR conditions and light winds are expected to prevail
through Sunday afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
Nice weather will remain for Southcentral Alaska well into Sunday
before a shortwave from the south will bring cloud cover across
Southcentral Alaska and light rain to the north Gulf coast and
Kodiak Island Sunday night. The rain will increase on Monday for
the north Gulf coast and Kodiak Island as a front moves in from
the south which will also further increase sky cover for the more
interior locations of the southern mainland. On Tuesday, rain
will diminish along the north Gulf coast but continue for Kodiak
Island.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure over the mainland will keep Southwest AK dry through
most of the day on Monday as offshore flow maintains mostly clear
skies. There is some potential for patchy fog development the
next few nights as high pressure settles in within a weak warm air
advection regime, however the continued offshore flow and dry
ambient conditions will serve the keep any fog localized in
nature to portions of Greater Bristol Bay and the Kuskokwim
Delta. The chance for precipitation will return to coastal areas
by late Monday as a weakening Bering front approaches the
mainland.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Benign cloudy conditions will persist over much of the region
into Sunday as a front deteriorates over the Central Aleutians
and a col region remains over the eastern half of the Bering. The
next front will eventually bring another round of precipitation
and stronger winds to the region through Monday as it enters the
Western Aleutians late tonight and then tracks eastward to the
Akpen by Monday evening. Storm force winds will develop over the
Western Aleutians and surrounding waters by Sunday night as the
parent low moves into the Bering, aided by cold advection on the
back side of the system.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The weather pattern next week will undergo a gradual transition
as the weakening ridge over Mainland Alaska is pushed north and
large scale upper level lows along the Aleutians and over the Gulf
of Alaska become the dominate weather features to influence
southern Alaska. Early in the week, an upper low over the Bering
and one well south of the Gulf will merge Tuesday into a broad
multi-center low over the Gulf as the two features track east and
north respectively. Troughs and associated surface lows will
rotate through the Gulf around the periphery of the broad low
Tuesday and Wednesday.

The next low coming in from the west will track along and south
of the Aleutians Tuesday night and Wednesday to get pulled into
the large scale Gulf/North Pacific upper low low circulation
around around Thursday. By Friday another equally large upper
level low will become established centered off of the Kamchatka
Peninsula but extending over the western Bering, western Aleutians
and extending well south into the Pacific. The presence of these
two large upper level lows will help to amplify the upper level
ridge building in between them over the central and eastern
Aleutians and Bering on Friday.

By Saturday the upper ridge shifts east to the Alaska Peninsula
and Southwest Alaska and then continues to build over Mainland
Alaska Sunday and Monday with developing north Pacific frontal
systems starting to push back into the Aleutians around this time.
The net effect of all of this looks like continued relatively
quiet weather with a gradual warming trend through the week
(though dependent on cloud cover for how much of a warming trend)
and the potential for more rapid warming next weekend if the upper
level ridge does indeed push east over Mainland Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 127 173 175 176 177 185. Storm 178.

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...JR