Small Craft Advisory 60, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
359 AM AKST Sat Jan 20 2018

.ANALYSIS AND UPPER LEVELS...
The longwave pattern features a building ridge over the Bering
Sea and a trough with an axis spanning from the north slope and
into the Gulf Of Alaska. A shortwave continues to round the top
of the ridge and into northwest Alaska. Anomalously cold air has
been observed and expect this Arctic outbreak to impact the
Bering Sea and mainland Alaska. Ahead of the ridge, there is a
quasi-stationary weak low over the Gulf of Alaska which continues
to produce showers that are detectable on the Middleton Island
radar. West of the strengthening upper level ridge, a gale force
low with an occluded front is approaching the western Aleutians
and is also advecting warmer air towards Attu and Shemya.

&&

.MODEL DISCUSSION...
Models are in good agreement with the synoptic features and they
continue to exhibit good run to run continuity. The biggest
forecast challenge continues to be the duration and the areal
coverage of the fog and stratus in Southcentral. Fog is commonly
handled poorly by the models. The fog and stratus coverage will
have an impact on the temperature forecast. Places where the skies
clear out will experience radiational cooling and possibly be
colder than anticipated. Other than the temperature and the
fog/stratus issues, this is a high confidence forecast package.

&&

.AVIATION...
PANC...Light winds expected. The latest satellite imagery still
has stratus and fog over portions of Cook Inlet and along Knik
Arm. Vicinity fog remains in the TAF for PANC. Amendments may be
needed.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: through
late Sunday)...

Little change in the overall forecast philosophy has changed.
Cold air over the interior continues to push through the gaps in
the Alaska Range. Strengthening thermal and pressure gradients
are giving rise to locally strong gap flows along the north Gulf
coast/eastern Kenai Peninsula, and some inland near channeled
terrain. Fairly pronounced wind gusts(gale strength) are also
flowing through gaps in the Aleutian range over the western Gulf
marine areas. Generally windy conditions in the aforementioned
areas are expected to continue into Sunday, but should diminish
some along the North Gulf Coast with increasingly unfavorable
upper level support and weakening pressure gradients. A low and
its associated fronts moves west across the Gulf Sunday/Sunday
night bringing increased changes of snow to the North Gulf coast
and eastern Kenai Peninsula.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Over the next couple of days the story remains the same for the
southwest Mainland, as arctic air pours into the region and causes
persistent offshore flow and declining temperatures. This will
continue to push both daytime highs and lows downward with
increasing threats for bitter wind chills approaching -40F. This
will be most likely where the winds are the strongest, so it is
likely the Kuskokwim Delta will realize the coldest wind chills.
The one change in this forecast is it seems more likely that a
weak low will move into the Kuskokwim Delta, bringing some light
snow to the coast this evening. Otherwise, cold and windy
conditions with clearing skies will resume on Sunday and carry
into early next week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure settling over the central part of the Bering Sea
will induce more of an easterly flow component as cold air pours
over the eastern Bering Sea and a gale force front moves into the
western Aleutians then stalls. This front looks like it will not
make further progress than the western Aleutians, so increasing
winds to gale force will be the biggest impact with this front.
With cold air pouring over the Bering Sea, expect freezing spray
to be a threat from the Pribilof Islands eastward.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Colder than normal temperatures continue through the next week as
a ridge pattern dominates the Bering. Low pressure systems wobble
on either side of the ridge, with one along the gulf and the
other just south of the western Aleutians. This pattern keeps a
drier pattern across the southern mainland with scattered showers
mainly along area waters. Confidence is higher than normal for
the extended forecast as models are trending toward similar
solutions. WPC solutions incorporated use of the operational
ensembles of the GFS and ECMWF which maintains consistency along
the active low centers.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 411 150 155 165 177 178 180 130 131.
         Heavy Freezing Spray 160 180 181 130 138 139.
&&

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