Small Craft Advisory 311, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
329 PM AKDT Mon Apr 16 2018

.ANALYSIS AND UPPER LEVELS...
The ridge that has been over the mainland part of the state the
past few days is weakening as the center is moving northward into
the Arctic. Enough of a ridge is still over the eastern part of
the forecast area (as far southwest as Anchorage) to keep most of
the clouds at bay today. However, the front in southwest mainland
Alaska and the western Gulf of Alaska is keeping the
precipitation in those areas. This front can be seen on IR
satellite elongating with warming cloud top temperatures
indicating that it is weakening. The 250 mb jet stream is becoming
a bit more zonal running west-to-east over the Aleutian Islands.
The whole jet is edging southward and should be south of the
Aleutian Islands by late tonight. The low near Attu is tracking
steadily eastward as it brings widespread gales and some storm
force winds to marine areas in the Bering Sea and Aleutian
Islands.

&&

.MODEL DISCUSSION...
Models continue to have great agreement through most of the week
with small divergence in low tracks beginning by Friday. Even
these differences are not likely to make major changes in the
forecast. The biggest element of interest where the model
solutions will have the greatest impact will be this weekend as a
cold upper level low digs southwestward from the Yukon Arctic
coast. The 12Z ECMWF has a somewhat stronger 500 mb low moving
over Nunivak Island Saturday afternoon while the GFS is a little
weaker and 400 miles farther east. The existence of the upper
level low and its movement into mainland Alaska looks likely, but
this difference in tracks will have a large impact on the weather
for both Southcentral and Southwest mainland Alaska.

&&

.AVIATION...
PANC...VFR conditions will persist through Tuesday afternoon.
Winds will remain the only real potential impact to the PANC TAF
through Tuesday afternoon. This evening may see a period of
southeast winds but the Turnagain Arm winds will not be very
strong which should limit potential winds to 10 kt this evening.
Late Tuesday afternoon will likely be a different situation as the
Turnagain Arm winds will be stronger and more likely to bend into
the airport late afternoon into the evening with gusts in the 20
kt range.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
The front over the western Gulf that extends through Kodiak Island
and out over southwest Alaska has stalled and is bringing rain to
Kodiak Island and southern Kenai Peninsula. It will remain in
place until Tuesday when another approaching system will push it
north. As it approaches the north Gulf coast, easterly winds will
increase along the coast and for east/west oriented gaps such as
the Turnagain Arm area. The front will then bring rain to areas
all along the north Gulf coast with some higher elevations seeing
snow into Wednesday. The front from the new system will follow
close behind the first front making it to the north Gulf coast by
Wednesday afternoon adding another wave of precip to the area.
Precip will continue but diminish through Thursday for areas along
the north Gulf coast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Moving into Western Alaska is a decaying occluded front. There
are some isolated showers on the radar at King Salmon but the
Bethel radar is pretty dry. The front will continue to get sheered
apart as it moves towards the interior. The Alaska Range can
still anticipate more QPF from this boundary tonight but otherwise
there is not too much more in store from that system. The next
storm will follow quickly in its wake and expecting the next round
of precipitation as early as tomorrow morning for places like
Kipnuk and Togiak. At this stage it looks like it will start out
as a rain/snow mix and then change over to rain.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The next in a series of lows has already moved into the Western
Bering/Aleutians, with the occlusion bisecting the chain. This
system will push into the Central Bering with the front holding
together this forecast period. The thickness packing retains its
thermal ridging into Wednesday which implies that the occlusion
will be slow to decay. The latest ASCAT (advanced scatterometer)
pass only sampled the Eastern Bering which was pretty tame at the
time of sampling but the models suggest that widespread gales will
impact the Western/Central Bering tonight and tomorrow.
Additionally, most of the operational runs ping into storm force
winds materializing south of the chain. Once this low gets into
the Central Bering, it really starts to slow down.

&&

.LONG TERM FORECAST (Thursday through Monday)...
Southeast flow and wet weather will continue on Thursday across
the Gulf coastal areas, with persistent cloudcover across interior
areas and parts of Southwest Alaska. On Friday and Saturday, an
upper low will start to dig down from the northeast across the
mainland, which will pull shower activity inland across Cook Inlet
and perhaps even into Southwest Alaska as the upper low drops
into the longwave trough that will be persisting over the eastern
Bering. A storm on Sunday will approach the state and, depending
on the strength of the aforementioned upper low, will start to be
pulled northward toward southern Alaska. There is still quite a
bit of uncertainty with where this low will end up, but its likely
the Gulf Coastal areas will see another round of steady rain
develop on Sunday and continue through the start of next week.
Overall, the forecast for most of the state is fairly cloudy with
near-normal temperatures, which will be a change from the endless
sunshine Southcentral has had recently.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 176 177.
 Gale Warning 119 130 155 160 165 170>175 178>181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
LONG TERM...AD