Small Craft Advisory 304, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 PM AKDT Thu Apr 12 2018

.ANALYSIS AND UPPER LEVELS...
The upper level map shows a weak low over the Gulf of Alaska with
some ridging over the eastern Interior. The jet stream is running
over the western Aleutians and then diving southeastward and under
the Gulf low. This jet stream position is favorable for the
strengthening of the surface low near the Kamchatka Peninsula and
that is reflected on the computer models.
The surface pressure pattern is allowing the interior and
Southcentral Alaska to clear out nicely with weak high pressure
over the mainland part of the state. A vertically stacked surface
low in the Gulf will continue to bring some clouds to the Gulf and
extending into the Bering Sea and parts of southwest Alaska.

&&

.MODEL DISCUSSION...
In the eastern parts of the forecast area the models have been
very similar with no big concerns. The high-resolution NamNest was
consulted for wind details through channeled terrain.
The Bering Sea is a little different story as a significant spread
in model solutions emerges by Saturday in regards to the low
center in the western Bering Sea. The GFS was viewed as the best
solution, but the ECMWF is very close.

&&

.AVIATION...
PANC...VFR conditions will persist. The only real uncertainty
regarding the Anchorage TAF is whether some Turnagain Arm winds
clip the airport this evening or not. Most recent data looks like
the strongest winds should miss the airport to the south, but it
is not out of the question that a few gusts make it into the
airport this evening before ending by midnight.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Multiple weak lows circulating around the northeast Pacific and
Gulf of Alaska, and lingering low level instability will continue
to bring showers across the Gulf region through Friday night. Some
weak upper level waves passing over the Copper River Basin will
also keep a chance of showers over the area through Saturday. The
pattern will undergo a change over the next couple days as the
low circulation shifts southward into the Pacific, and steering
flow over Southcentral shifts to northerly as a high amplitude
ridge approaches from the Bering Sea on Saturday. This will
establish an offshore flow pattern over Southcentral Alaska,
bringing a drying trend through the weekend.

&&

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

The same general upper air pattern is finally begin to shift away
from southeast flow. The last shortwave trough is moving across
the Kuskokwim Delta and westward into the Bering Sea. There are a
few lingering showers leftover, but expect rapid drying overnight
as shortwave ridging begins to build in. Some fog is expected
overnight given the slack winds, but it should not be widespread
dense fog. Dry conditions will then persist through most of
Saturday before a quickly moving warm front approaches the coast.

&&

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

Broad cyclonic flow exists over most of the Bering Sea with an
approaching warm front over the western Bering. This system will
become the dominant system the next two days as it strengthens
rapidly into a powerful near storm force low over the western
Bering Sea Friday night through Sat. The associated gale force
front will reach the eastern Bering by Saturday afternoon as the
low undergoes rapid occlusion.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A ridge pattern over the eastern mainland keeps most of
Southcentral dry for the end of the weekend. A strong storm system
centered over the western Bering slides a front through the
southern and eastern waters Saturday night. The boundary lines up along
the west coast and slowly pushes rain inland through Sunday
morning. A strong wave of energy riding up from the North Pacific
keeps higher rain chances across the eastern Bering and west coast
through Sunday night. This next wave is expected to kick the
surface front into eastward motion on Monday spreading rain to the
Alaska and Aleutian ranges. There is still a bit of uncertainty
with the eastward progression of this front through Wednesday as
models are struggling on how to resolve the eastern Bering low
with another Pacific front racing in from the west, while yet
another wave plunges south over the Alcan border.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales 173-178 185 411-413.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...KH