Small Craft Advisory 268, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
400 AM AKDT Fri Mar 30 2018

.ANALYSIS AND UPPER LEVELS...
The longwave pattern is dominated by a building upper level ridge
over the Bering and a weakening upper level trough over
Southcentral. At the surface, high pressure is spreading over the
western half of the state leading to clearing skies and light winds,
though fog has developed over the Bristol Bay area as a result. A
very weak surface trough extends across the Gulf Coast into the Cook
Inlet area bringing increased cloudiness with a few isolated snow
showers over the Chugach Mountains and even a stray shower over the
Anchorage Bowl this morning.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement for most of the
forecast period, all showing a large closed high building over
most of the state this weekend. The models have been struggling
with some of the finer details of the forecast including fog over
Bristol Bay and the spotty showers over southwest and
southcentral. Overall forecast confidence is high through the
weekend.

&&

.AVIATION...
PANC...Radar currently shows a few isolated snow showers moving
south across the Anchorage Bowl, with Ft. Richardson reporting
MVFR ceilings. Thus a short period of ceilings below 3000 ft and
some light snow can be expected over the terminal early this
morning before VFR conditions and light winds take over and
persist the rest of the TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level low is over southcentral Alaska as of early this
morning as it cuts off and moves into the Gulf of Alaska today.
There are some isolated snow showers near the low center but these
will dissipate by mid morning. The low moving into the Gulf will
bring in some somewhat gusty winds to coastal areas and through
channeled terrain, but the lack of cold air to the north will
mitigate the strength of the gusts.
Other than that, there should be decreasing clouds by afternoon
over most of the region with the Copper River Basin likely the
last area to clear out.
A shortwave in the interior will move over the northern Susitna
Valley and Copper River Basin Saturday and Saturday night, but it
looks like it should just bring some mid-to-high level clouds
without any precipitation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure over the eastern Bering will remain the dominant
feature through this weekend, bringing a stretch of dry weather
and sunny skies to much of the southwest mainland. The fog threat
will hang on for one more night, particularly across the Kuskokwim
Delta as warm advection works into the area with the eastward
advance of the ridge. Increasing offshore flow this weekend should
help to limit fog potential in subsequent nights.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The Bering will stay largely quiet through the weekend as the
closed upper high remains overhead. This will keep one front
confined to the far western Bering and another front just south of
the Aleutian chain into Saturday. Rain will then begin to work
back into the chain Saturday night and Sunday as the ridge shifts
north towards Saint Lawrence Island, allowing the North Pacific
front to move over the Central Aleutians. This feature will also
be accompanied by gale force winds and higher seas on the Pacific
side of the chain.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast begins Saturday night with dominant high
pressure over the eastern Bering. There is good consensus amongst
the models with this setup leading to an outflow pattern for the
southern mainland. This setup will remain into early next week
when the high pressure diminishes and moves west. There is also
good agreement of an upper level low developing over mainland
Alaska as the high diminishes. However, guidance varies greatly
on where this low will setup and its timing. This will play a big
factor in the type of weather that will develop over the southern
mainland. Due to the uncertainty by mid next week the ensembles
were preferred for that time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales 172 174 176.

&&

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