FXAK68 PAFC 230128
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 PM AKST Wed Nov 22 2017
.ANALYSIS AND UPPER LEVELS...
The frontal system over the Bering is beginning to spread snowfall
along with gusty southeasterly winds into the Kuskokwim Delta and
Western Bristol Bay. This front is part of a much larger system
that is taking up most of the Bering Sea, with a good supply of
cold/dry air advecting into the low allowing for continued
intensification as it moves onshore. This surge of cold/dry air
also helping to bring gale force winds throughout the Central
Bering, which are expected to increase to widespread storm force
as it moves into the Eastern Bering/Aleutians. Over the Gulf and
Southcentral, conditions are much quieter than the Bering with a
brief break from the active weather in a continued progressive
pattern. This will begin to break down late tonight as the frontal
moving through the Southwest Mainland produces a triple point low
in the gulf.
The models remain in very good synoptic agreement in the early
term before starting to break down early Thursday with the
positioning and intensity of the triple point low in the Western
Gulf. In particular, the GFS continues to be both the deepest and
furthest west with that low, and was generally ignored today in
favor of the further east/weaker solutions of the NAM and EC.
These differences then become larger on Friday with large
differences in how quick the low will depart the southern Gulf, the
NAM being the slowest. The speed that this low departs the Gulf
will weigh heavily in how strong winds over the North Gulf Coast
and will need to be monitored as trends towards the NAM position
will produce stronger winds than currently forecast.
PANC...VFR conditions with light winds will continue today, before
ceilings near 5000 ft move into the area beginning late tonight.
There may also be a few flakes as ceilings drop on Thursday
morning, however these are expected be very light with VFR
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 2)...
Dry weather prevails across the southern mainland through Friday
evening as an offshore pattern persists. Active weather across the
Southwest mainland brings a front across to the western gulf
tonight spreading precipitation across much of the gulf including
the Kenai and Kodiak Island through Thursday morning. The front
weakens as it slides across the central waters Friday afternoon
then remains stationary and diminishes heading into Saturday
The main concern surrounds offshore winds for typical gusty areas
through channeled terrain. As the surface low moves into the gulf
late Thursday night a ridge shifts from the Yukon Territory to
the central interior. The ridge forces a cold dense air mass
toward the coast which actively increases winds overnight Thursday
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Gusty winds and widespread snow associated with the Bering storm
will continue to impact portions of southwest Alaska. At times,
the models ping into moderate to heavy snowfall. Periods of
blowing snow and white out conditions are also possible tonight
and tomorrow morning. The frontal boundary will move inland and
stall near Bethel, then slowly decay. Cold and drier air will be
steered into the region Thursday night. Isolated showers will
linger over the region through the end of the period but
significant accumulations not expected after Thursday.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The forecast period commences with an unsettled pattern in place,
complete with wintry precipitation, strong winds and rough seas.
The latest scatterometer pass has the Bering front east of the
Pribilof Islands this afternoon. Behind the low center, widespread
northwest flow and strong cold air advection. A tight pressure
gradient will continue to bring strong winds to much of the
Bering and the Central/Eastern Aleutians. The winds will gradually
diminish for all areas from west to east for the Bering and the
Aleutian archipelago by Friday morning. Looking upstream, a dome
of high pressure will build into the Western Aleutians early
Thursday with the ridge axis east of Atka by Friday morning.
.LONG TERM FORECAST (Days 3 through 7)...
The long term portion of the forecast begins Friday night with a
familiar outflow wind pattern in place across much of southern
Alaska, with a ridge over the Bering Sea and a longwave trough
extending along the Alcan border into the eastern Gulf. This will
keep most of the area cold and dry well into the weekend before
the ridge breaks down and the pattern begins to shift once again
Sunday into early next week.
Forecast confidence quickly diminishes by the beginning of next
week as a deep trough over eastern Russia sends a series of
shortwaves into the Bering Sea. Models continue to show poor
agreement with respect to the evolution of these waves and
subsequent development and placement of surface features. It
appears that a deep low will rapidly intensify over the Bering
Saturday night and then move to the general vicinity of the Alaska
Peninsula by late Sunday, sending a front near the southwest
coast and bringing the threat for another round of mixed
precipitation and gusty winds to portions of Southwest AK. An even
deeper low then looks to approach the Aleutian chain on Monday,
bringing stormy conditions to the southern Bering with the details
largely dependent upon the track of the low through the middle of
the week. Guidance is also hinting at another system moving into
the western Gulf in the Monday/Tuesday time frame, but confidence
is low at this time as specific solutions remain all over the map.
Generally speaking, those in southern Alaska can expect chances
for precipitation to increase through the first half of next week
(especially along the coast) as temperatures rebound closer to
seasonal normal values.
PUBLIC...CFW 155 161, NPW 181 185 195, WSW 155 161.
MARINE...Storms 150 155 165 170-171 179 180 181 185 412-414.
Gale 121 130-132 138 165 173-175 178 352 411.
SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS