Small Craft Advisory 998, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 AM AKST Thu Dec 28 2017

.ANALYSIS AND UPPER LEVELS...
An upper level ridge over the Northern Gulf of Alaska and extending
up into NW Canada is flattening between two upper level lows to
the north and south. Underneath this high, mostly clear skies,
cold surface temps, and a strong low level subsidence inversion
are leading to widespread fog and low stratus across the
Anchorage Bowl and down into the northern half of the Cook Inlet.
Low clouds and fog have also been persistent over the Copper River
Basin as well as over Southwest Alaska including the Kuskokwim
Delta and the Bristol Bay side of the AKPEN. Further west, a large
upper level ridge centered over northwestern Siberia is
dominating the weather over most of the Bering and Aleutians. A
low south of Attu Island is moving north but is beginning to stall
out as it runs into the dominant high. A front out ahead of the
low is beginning to move over the island chain bringing rain and
upper end gale force winds from Shemya to Atka.

&&

.MODEL DISCUSSION...
Models are in good agreement this morning regarding the
evolution and progression of the major synoptic scale features
through the end of the week. All models show a broad double
barrel low forming along the Aleutian chain by Friday but begin
to diverge on Saturday regarding the development a third low
center that looks to wrap up around from the south into the AKPEN.
The GFS was the outlier during this time period so stuck mainly
with the NAM and EC for the morning forecast package, which brings
a front into the Gulf of Alaska by early Sunday morning.

&&

.AVIATION...
PANC...Though the most recent obs (1253z) show VFR conditions at
the airport, this should only be temporary as area webcams still
show the fog monster lurking around in the Anchorage Bowl,
waiting to attack any unsuspecting victims. So LIFR conditions
will be in and out through the morning then should see some more
persistent clearing later in the afternoon. The real question is
whether or not fog builds back in again this evening. The upper
level ridge will break down some allowing in a bit of mid-level
moisture and SW'ly flow. On the other hand, weak surface flow and
lack of mixing will keep the surface inversion in place, so no
reason, especially this time of year, that fog/stratus won't
redevelop and move back in again this evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The generally benign pattern will continue across Southcentral
into Friday. Stable conditions inland will likely allow for fog
to continue across the Anchorage Bowl and the Copper River Basin
into Friday. Relatively cold temperatures will continue inland
into Friday with weak offshore flow continuing across the North
Gulf Coast. A weather front moving north on Friday will bring a
mixture of rain and snow to Kodiak Friday evening, increasing
chances of snow to the Southern Kenai Peninsula late Friday night,
and increasing winds to the western Gulf.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Forecast challenges continue to be clouds and temperatures over
the mainland. Where low clouds hang around, temperatures will
remain in the teens, but where they clear, temperatures will
plummet into the single digits or lower pretty quickly. Expect
clearing over the Kuskokwim Delta today, followed by low
temperatures below zero tonight. Low clouds should stick around
the Kuskokwim Valley through tonight, keeping temperatures from
falling off too far. Greater Bristol Bay is a bit more
challenging, but expect low clouds to hang around through the
morning hours and possibly longer. The pattern begins to change on
Friday as a front begins to bring some southeasterly winds and
warmer temperatures to the area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A gale to storm-force front will roll up on the chain today
bringing rain and snow to the southern Bering Sea. The front will
come to stall in place for the next few days as several more
disturbances spawn low pressure systems along it, each one further
east than the last.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The models remain in great agreement in the general pattern of a
return to a much more active and warmer pattern for the South
Mainland into the new year. This will occur as the same pattern
that brought widespread warmth to this same area earlier this
month redevelops as a broad ridge from the coast of California
noses up into the Panhandle with a continued persistent trough
over the Bering. This will leave the Gulf/South Mainland under the
influence of a southerly jet that is expected to bring a series
of northerly moving systems into the South Mainland through the
middle of next week. The first (and likely coolest) of which is
expected to bring gale force winds from the Gulf into the Eastern
Bering for Sunday, along with snow, possibly mixed with rain to
the Gulf Coast. The active pattern is then expected to continue
into Mon-Tue a second stronger and warmer system moves into the
region. As is usually the case in the models as these large scale
pattern changes are occurring, model agreement in the exact track
of these systems is poor, leading to low confidence in the details
in the forecast. What is much more certain is a shift back to a
warmer and wetter pattern with the potential for more wind events.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Fog Advisory 101.
MARINE...Gale 155 170-176 179 185 412-414.
         Storm 177 178 411.
 Heavy Freezing Spray 160 180.

&&

SYNOPSIS AND MODEL DISCUSSION...KVP
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...DEK