Small Craft Advisory 209, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 AM AKDT Sun Mar 11 2018

.ANALYSIS AND UPPER LEVELS...
The latest satellite image depicts a low southeast of Middleton
Island with a ridge over the Aleutians and a moisture surge that
is riding up the backside of that ridge. A broad upper level
trough stretches from the South Mainland into the Gulf, which
continues to bring produce showers over portions of Prince William
Sound and the North Gulf Coast. The latest scatterometer data
pings into another surface low near Northeast Russia which is
producing gale force winds.

&&

.MODEL DISCUSSION...
The models are in good synoptic agreement for the first 24 hours.
Past Sunday, the main eye sore is the low moving towards the
Central Aleutians, with the ECMWF being the most bullish with the
track of the low. The track continue to look good for the Prince
William Sound low. However, there are still some timing issues
with the precipitation shield, but good confidence in another snow
event for portions of PWS including Valdez and Cordova.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist today and
Monday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A low in the northeast Gulf will move into Prince William Sound
today. Precipitation will quickly spread westward today, reaching
Cordova, Valdez and Glennallen early this morning, Whittier by
late morning and then possibly to Anchorage and the Matanuska
valley this afternoon. The precipitation will stall in its
westward progress late this afternoon as the low moves inland and
dissipates. With Anchorage and the Matanuska Valley at the west
end of the system, snow amounts (if any) in these areas should be
light. The precipitation is expected to fall as snow, except some
rain should mix in near Cordova by this afternoon.

On Monday two systems will approach the area, one from the
southwest and one from the southeast. The southwest system will
weaken as it reaches Kodiak Island Monday morning and then break
apart as it reaches the Kenai peninsula Monday afternoon. The
southeast system will bring precipitation into Cordova, Valdez and
the eastern Copper River basin beginning in the late afternoon
and evening hours. How far west the precipitation moves is a low
confidence forecast as the models are not in very good agreement
on this.

&&

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

Besides low stratus and possibly a few passing flurries this
morning, dry weather will prevail today before another front moves
inland this evening. This will bring widespread snow to the
coastal locations, along with some blowing snow along the
immediate coast. This front will move inland tonight then weaken
on Monday with snow total accumulations ranging from 1-3" inland
and 2-4" along the coast. Dry conditions build back in Monday
night.

&&

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

A warm front stretching over the Central and Eastern Aleutians and
Pribilof islands will bring rain and snow and gale force winds
before reaching the Southwest coast tonight and weakening. Another
warm front and weaker surface low will move into the Western and
Central Bering/Aleutians and move eastward toward the coast
through Tuesday. &&

.LONG TERM FORECAST (Days 3 through 7)...
The long range forecast begins Tuesday with a relatively quiet
weather pattern over the southern mainland and most of the
Aleutians/Bering as the area lies in a transition zone between
systems. A nearly stationary surface low will be present over the
Northern Pacific/Southern Gulf of Alaska which could bring some
snow to the Gulf Coast on Tuesday before being kicked east by a
building longwave ridge, bringing pleasant mid-week weather to
southcentral.

A persistent long wave trough over the Bering will begin to re-
amplify Wednesday as waves rotating around the base of the trough
will kick off several low pressure systems through the week. The
upper level jet over the Bering will become more
west/southwesterly by mid week which will help to tap into
subtropical moisture to the south and advect it north towards
mainland Alaska. At this point, the long range models fall out of
agreement regarding the placement and even timing of the various
lows tracking out of the Bering, with models becoming 180 degrees
out of phase with each other by the end of the week (trough vs
ridge), so there is little confidence in the timing of specific
systems late next week. Regardless, there is consensus in an
overall anomalous and active pattern for mid March as the
persistent upper level trough over the Bering Sea drives the main
storm track into mainland Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 119 412 413 414 165 172 173 174 175 176
         177 178 180 181 185.
Heavy Freezing Spray 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...KVP