Small Craft Advisory 213, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
834 AM AKST Sat Mar 11 2017

.ANALYSIS AND UPPER LEVELS...
Water vapor satellite imagery shows an expansive ridge anchored
over the Central Bering this morning with a closed low to it's
north over the arctic. A shortwave diving from the arctic low is
spreading some mid level clouds over the Southcentral Region this
morning; otherwise mostly clear skies prevail across the southern
mainland.

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.MODEL DISCUSSION...
Models continue to remain in good agreement with no significant
changes in the East. In the West, the NAM-Nest was the preferred
model, and the forecast confidence remains high through the
weekend.

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.AVIATION...
PANC...VFR conditions with northerly offshore winds through
the weekend.

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.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level high over the western Bering Sea will slowly
retrograde through Sunday night. At the same time, an upper level
low over the Northern Panhandle will drift westward. Considerable
clouds are over Southcentral Alaska this morning due to a vort-
max sliding through the area in the northeast flow aloft.
Conditions should clear later today as the vort-max moves into the
Gulf. By Sunday night, the proximity of the Panhandle low will
increase the winds through Thompson Pass, Valdez and the Copper
River delta.

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.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Near normal temperatures will continue through the weekend before
the next arctic air mass begins to drop south early next week.
Sunny skies and light winds will be a common theme through the
short term as a blocking pattern remains well entrenched across
the region.

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.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Broad upper level high pressure continues to dominate the Bering
sea with a newly formed rex block centered over the region. This
has allowed winds to diminish and rainfall/snowfall chances have
become rather minuscule. Pockets of stratus and high clouds will
be observed across the Bering through the weekend but fog chances
should be kept at bay by how dry the boundary layer has become
(see previous 2 PACD RAOBs).

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.LONG TERM FORECAST (Days 3 through 7...Mon through Fri)...
A pattern change will slowly unfold. This occurs as the ridge
over the Bering very slowly creeps to the west and allows more
energy to spill over the mainland. The energy helps to carve out a
deep longwave trough that will extend from the Arctic through the
Gulf of AK. Within this trough will be plenty of very cold air.
The 850hPa temperatures over the Interior look to drop to just as
or nearly as cold as they were during the past week. It does look
like the AK Range blocks much of this cold air from intruding
into Southcentral AK. While the Southwest AK will not be so
fortunate with low temperatures looking to plunge well below zero
by the middle of next week. As this colder air works in, there
could be some light snow that makes it over the ridge. The more
likely impact will be some gusty winds with the robust cold air
advection. As this cold air spills off the edge of the ice pack
over the open Bering waters, there will be widespread snow showers
spreading across the Aleutians.

The other interesting aspect of the pattern change will be lower
pressure developing in the northern Gulf of AK. There is still a
fair amount of uncertainty with any surface low center that would
develop. However, it does look like enough moisture will make it
back in to the coastal areas that we have increased the snow
chances across that region. If moisture can swing far enough west
into the very cold air, it could lead to some snow threats for
interior portions of Southcentral towards the latter half of next
week.

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.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

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SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...MO