Small Craft Advisory 285, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 AM AKDT Sat Mar 28 2020

.ANALYSIS AND UPPER LEVELS...

A broad upper trough and associated surface low and weak frontal
boundary over Southwest Alaska is producing snow across the
western Mainland. Westerly flow across the Alaska Range has left
Southcentral largely on the dry side with little snow reported
except perhaps along the Talkeetna and Chugach Mountains. Gusty
winds on the backside of the surface low is producing some areas
of blowing snow across the Kuskokwim Delta. Weak outflow
conditions were observed across Southcentral with higher pressure
inland and weak low pressure over the Gulf.

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.MODEL DISCUSSION...
Models are in generally good agreement through Sunday night.

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.AVIATION...
PANC...Generally VFR conditions. Cold advection will increase
northerly winds across the airport complex tonight and Sunday.

&&

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

An upper trough over the Mainland is producing broken cloud
cover over Southcentral, but very little in the way of
precipitation. The main story will be the strong outflow winds
which will develop tonight as the upper trough drives south into
the Gulf and sets up northerly winds aloft which is favorable for
the enhancement of outflow conditions. In addition, cold
interior air spills into Southcentral and increases the
thermal/pressure gradients between the Gulf waters and land
areas. The combined ingredients will result in the development of
strong outflow wind conditions along the north Gulf coast,
through gaps in the ALaska Range, and across the Matanuska Valley
tonight through Sunday.

&&

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

A surface low in the northern Bering will make its trek inland
across Southwest Alaska this morning, which will help to keep
snow showers in the forecast through this afternoon. Snow will
taper from the Kuskokwim Delta late morning as the front
continues to move southeastward, allowing for snow showers to
linger across Bristol Bay throughout the day. Light snow
accumulations can be expected with this weakening system.

As the aforementioned low departs into the Gulf by late this
afternoon, strong north to northwesterly onshore flow could cause
some of the fallen snow to blow around, especially along coastal
locations. Cold air advection will continue to move in as this
low exits the region, causing a cooling trend through the weekend
as a polar high build across the southwest. Temperatures on
Sunday will be a lot cooler than today's high temperatures, with
high temperatures barely reaching the mid-20s across the area.
Expect low temperatures tonight and Sunday night to be in the
single digits as colder air remains in place.

&&

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

Strong north to northwesterly gale force winds over the eastern
Bering will weaken through Sunday morning as a low positioned in
the northern Bering moves inland. Meanwhile, the high pressure
and quiet conditions over the western Bering this morning will
come to an end later today as a front begins to move into the
region. There is still some uncertainty with the associated low
in the northern Bering in terms of strength and position.
However, as this front moves eastward to the central Bering for
Sunday afternoon, there is more confidence today that winds will
strengthen to gale force as it approaches the Pribilofs.

Cold temperatures continuing to move into the eastern Bering
today through Sunday will keep heavy freezing spray in the
forecast, as well as strong winds through bays and passes of the
eastern Bering and Alaska Peninsula.

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

Bering Sea/Aleutians... A storm system will track across the
western to central Bering on Sunday. There is uncertainty in the
exact track of the low center, but high confidence in widespread
small craft winds with gales likely near the low center. The
eastern Bering will likely see minimal impacts from this, as most
model solutions track the low to the northern Bering, or even
into Russia. Forecast confidence for Monday/Tuesday drops
significantly, although it doesn't look like any major storm
systems will affect the region.

Gulf of Alaska... There is a high confidence in gap winds along
the Gulf coast on Sunday. These will diminish by Monday and the
overall weather pattern looks quiet.

&&

.LONG TERM FORECAST (Days 4 through 7/Monday through Friday)...

Guidance is consistent with the overall synoptic pattern on
Sunday with an upper level trough over the Alaska mainland while
upper level ridging slowly moves eastward across the central and
eastern Bering. This will result in cold temperatures across the
mainland. A high confidence exists with a warming trend in
temperatures across the Alaska mainland in particular Southwest
Alaska Sunday through Tuesday. However, there is low confidence
with respect to the magnitude of the expected warm up as there
are discrepancies between guidance with how fast this ridge is
moving. The GFS appears to have the fastest bias as the GEM and
ECMWF show the upper trough extending into the Ahklun Mountains
while the GFS has the trough only extending to the eastern AKPEN.
More significant differences between guidance arise on Wednesday
with respect to the amplitude of the upper ridge over
Southcentral Alaska. This means that there is a low confidence in
the temperature forecast as the placement of this upper ridge
affects the placement of the surface ridging and thus causing
major discrepancies in the temperature forecast. One area of
confidence for this period is the weather is expected to remain
benign across Southcentral during this time as high pressure will
be over the area. Significant discrepancies continue on Thursday
and Friday and thus the forecast confidence remains very low for
this period at this time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 127 150 155 165 180 181 185 412-414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...SB/ED