Small Craft Advisory 323, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
442 AM AKDT Fri Apr 10 2020

.ANALYSIS AND UPPER LEVELS...

With warm temperatures and increasing day light, snow continues
to melt around the region. At the NWS Office in Anchorage the
latest snow depth was 16 inches while the latest snow depth at
Valdez City was 75 inches. A dome of high pressure spans from
Kodiak to the Yukon Territory. Widespread subsidence has resulted
in dry conditions through much of the atmospheric column.
According to the AMSU (Advanced Microwave Sounding Unit) and the
SSMI (Special Sensor Microwave Imager) the precipitable water
value in the atmosphere is 60 percent of normal over portions of
Southcentral. Meanwhile, with the low north of Adak the same
satellite instruments pinged into to an excess of 200 percent of
normal for precipitable water values. And some of that Bering
moisture has slopped over into western Alaska, north of Bethel
which is consistent with radar imagery and surface observations.

&&

.MODEL DISCUSSION...

For initialization purposes, compared the precipitation on the
Bethel radar at 9z to the projected precipitation shield for 9z.
The Canadian, GFS, ECMWF and NAM all did reasonably well. At the
surface, the models are in decent agreement through Monday. Some
of the upper level energy for the same time frame is a skosh out
of sync but nothing in the category of specious. Starting Monday,
most notably in the North Pacific model divergence ensues.

&&

.AVIATION...

PANC...Early this morning the the Nighttime Microphysics
satellite image did not have any fog on it. With high pressure in
place expect VFR conditions and light winds will prevail through
the TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Sunday night)...

An upper level ridge will strengthen over Southcentral today,
leading to another sunny day and slightly warmer temperatures.
The ridge will then slide eastward, opening the way for deep
southerly flow from the North Pacific. A series of short-waves
and surface systems will begin to make their way northward toward
Alaska this weekend. A leading warm front will reach Kodiak and
the western Gulf on Saturday, bringing rain and windy conditions.
A surface low will follow closely behind, moving into the Gulf on
Saturday night. While there is quite a bit of uncertainty in the
track of this low, the end result will be to push the warm front
and associated precipitation northward into Southcentral saturday
night through Sunday night. Another storm will follow shortly
behind the first, with precipitation chances increasing late
Sunday into Monday. Temperatures will warm each day, so that by
the time precipitation overspreads Southcentral generally expect
rain and snow transitioning to all rain.

&&

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

Fair skies are expected today under an upper level ridge.
A much more progressive pattern will develop this weekend. A warm
front will begin to lift northward over the region on Saturday,
however widespread precipitation will not develop until Sunday as
a strong upper level low pushes the front onshore. While some
snowfall is likely along the Kuskokwim Delta coast on Sunday
morning when temperatures will be slightly below freezing, much of
the area will see mostly rain as temperatures will rise into the
40s across much of southwest Alaska. Gusty easterly winds are also
likely through terrain gaps over interior Bristol Bay. All of
this will accelerate snow melt.

&&

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

Scattered showers will continue through Saturday morning across
the western Aleutians as a low departs to the north. Weak high
pressure will build in its wake through Sunday bringing more
settled weather. Showers will redevelop Sunday evening north of a
warm front. Benign conditions are expected over the central and
eastern Aleutians today under an upper level ridge. Rain will
track across the region Saturday as a warm front lifts northward,
tapering off from west to east by Sunday ahead of weak high
pressure. Temperatures will rise over the coming days, potentially
warming to the upper 40s along the Alaska Peninsula by the end of
the weekend.

&&

.MARINE (Days 3 through 5/Saturday through Monday)...

Bering Sea/Aleutians:

The theme for this extended forecast will be warmer and wetter air
masses as a period of southerly flow begins thanks to a broad
area of high pressure over the Gulf of Alaska/Mainland Alaska. As
a frontal boundary lifts north out of the north Bering on
Saturday, high pressure over the eastern half of the Bering begins
to break down as a 1007 mb low in the north Pacific pushes a warm
front north into the eastern two thirds of the Aleutian Chain on
Saturday morning. This wave will push north of the Pribilofs
Saturday afternoon and keep western Alaska, Bristol Bay, and the
Alaska Peninsula in a wetter pattern through Monday morning.
Another warm front lifts into the Western Aleutians Sunday
afternoon, with its 995 mb parent low in the north Pacific set to
cross the chain late Monday night.

Gulf of Alaska:

The forecast period will start with dominant high pressure pushing
off to the northeast Saturday and a warm front lifting across
Kodiak Island Saturday afternoon as a north Pacific low pushes
into the Aleutians. This frontal boundary will maintain a presence
across the north Gulf Coast through Sunday night and then fade
Monday morning as high pressure builds back in from the east.

&&

.LONG TERM FORECAST (Days 4 through 7/Sunday through Wednesday)...

Model guidance has come into much better agreement for the Sunday
through Tuesday time period showing an upper level ridge in place
across much of Alaska with confidence very high. With this upper
level ridge in place, the warming trend will continue every day
into the middle of next week. For the mainland, expect
temperatures warming to near normal on Sunday and then to above
normal early next week. Unsettled conditions are also possible on
Sunday as a weak system from the North Pacific south of Dutch
Harbor moves northward toward Bristol Bay with high confidence for
this system. A different closed off system west of the Aleutians
Sunday will move east towards the Bering Monday due to the upper
level trough in place over eastern Russia and the North Pacific.
This may bring another period of unsettled weather to Southwest
and Southcentral Alaska Tuesday to Wednesday time frame next week
as it continues east but gets pushed north due to the blocking
ridge to the east. Confidence is average for this system.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 138.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...LB/MV