Small Craft Advisory 348, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 AM AKDT Mon Apr 20 2020

.ANALYSIS AND UPPER LEVELS...

A broad, disorganized area of low pressure continues to exist in
the Bering Sea. Another wave of energy is moving north through
the Gulf of Alaska and into Southcentral AK. The wave moving into
Southcentral is bringing warm, moist air with it. This is
creating rain showers, low ceilings and fog - especially in
coastal areas. Southwest Alaska is also seeing widespread low
level cloud cover and fog due to recent rain providing moisture
and weak high pressure that has now moved over the area. Overall,
pretty much all of our forecast area is dealing with cloudy and/or
foggy conditions this morning.

&&

.MODEL DISCUSSION...

Models continue to be in good agreement to start the week. Some
difference emerges in low placement for a compact upper level low
in the Western Bering on Tuesday. Outside of this feature,
guidance is on track for the next few days, meaning high
confidence in the forecast.

&&

.AVIATION...
PANC...Low level ceilings with light rain showers should persist
through the TAF period. Ceilings may drop to MVFR conditions at
times. Winds will remain light.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Overall the mean position of the upper trough will persist
over the Western mainland and keep generally broad
southerly flow aloft across Southcentral Alaska. At the
surface/lower elevations minor waves and frontal boundaries
moving north across the Gulf provide a moisture feed. Combined with
the upper levels, expect periods of rain/showers to persist across
the region through Tuesday with the brunt of precipitation along the
North Gulf Coast. Freezing levels overall stay above 3000 ft in many
areas. With the exception of gusty east winds across Turnagain Arm
and Small Crafts over the western Gulf, winds should be fairly light.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

Southwest Alaska can expect mild weather today. Lingering light
showers are possible for portions of SW AK but most locations will
be dry today. As the ridge gets shunted to the east, that will allow
the arctic trough to slide southward. The models ping into a
shortwave from the arctic trough moving north of Bethel tonight and
dropping further south on Tuesday. Sensible weatherwise, this
feature will allow slightly cooler temperatures into places like
Nightmute, Aniak and Bethel.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

At the onset of the forecast period there is a decaying low in the
Central Bering and a 979mb low in the North Pacific. On satellite
imagery there is another low circulation over the Western
Aleutians. On the longwave pattern, the ridge has shifted eastward
and the axis of the longwave trough extends from Kamchatka over
the Western Aleutians and into the North Pacific. The jet core at
the base of the longwave trough is at 32N. Gale force winds were
detected over night with the low near Attu and the low south of
Adak. This forecast period, the lion's share of the unsettled
weather will be in the North Pacific and Aleutians and the Bering
will have a lull in activity. The expectation is that the low
near Shemya will phase with the low in the North Pacific. Another
shortwave will descend from Russia into the Western Bering on
Tuesday, keeping the cold air advection on tap.

&&

Marine Discussion (Days 3 - 5: Wednesday through Friday)

Bering Sea/Aleutians…

Easterly flow will dominate much of the Bering through Tuesday
evening before shifting to a more northerly direction. Northerly
flow will be expected from Tuesday evening through Thursday. Winds
are expected to be below gales with no high seas expected through
Thursday morning. Guidance shows a front approaching the western
Bering Sea Thursday morning that may bring high end small craft/low
end gales but the strength and exact timing of this front remains
uncertain leading to a low confidence forecast.

Gulf of Alaska…

A front moving north through the Gulf of Alaska will allow for a
barrier jet along the Gulf Coast Tuesday morning through Tuesday
afternoon though remaining in the small craft advisory range. No
major weather features are expected across the Gulf of Alaska from
Tuesday afternoon through Thursday morning. The low that has been
sitting south of the Aleutian Chain will begin to move into the
region late Thursday morning into Thursday afternoon. Guidance
differs on the timing and the strength of this system as it begins
to progress eastward leading to a low confidence forecast. At this
time, it appears winds will remain below gales in the small craft
advisory range with no high seas expected.

Long Term Discussion (Days 4 - 8: Thursday through Sunday)

Overall, the long term weather pattern is looking active. A few
key features that models have been consistent with over the last
couple of days are an upper level ridge of high pressure in place
over Siberia and two upper level lows, one centered west of the
Bering over the Kamchatka Peninsula and the second centered south
of the Alaska Peninsula. By Friday, the low south of the AKPEN
begins to strengthen as it moves into the Gulf of Alaska for
Saturday. This will likely mean easterly flow across the northern
Gulf coast and scattered showers to start the weekend before
chances for precipitation increase as the low lifts northward for
the weekend. Meanwhile, a secondary disturbance spins up from the
primary Kamchatka low and moves west over the western Aleutians.
Precipitation with the leading edge of the front will likely start
on Thursday before becoming more widespread across the central
Aleutians by Friday. This low then moves south of the Chain on
Saturday. Northerly flow looks to return across the Bering for
Sunday as a large upper level trough remains in place over the
mainland while an upper level ridge attempts to build over the
western Aleutians by the end of next weekend.

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...KO