Small Craft Advisory 852, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKDT Wed Oct 31 2018

.ANALYSIS AND UPPER LEVELS...
An upper level ridge of high pressure remains in place along an
axis extending from Southwest Alaska into the Gulf. An upper level
trough situated just south of the eastern Aleutians is slowly
weakening.

Satellite imagery shows generally clear skies across much of the
southern mainland with some high clouds in place over Southwest
Alaska. In addition to high level clouds, moist low level air
coupled with subsidence from the building high pressure has
generated fog across Southwest mainland Alaska and areas along
the northern AKPEN, as well as across the Copper River Basin.
Along with clear skies in Southcentral, surface observations
indicate light northerly winds with gustier outflow winds in place
along the southern end of Cook Inlet.

&&

.MODEL DISCUSSION...
Model solutions remain in good agreement through the near term.
Minor disagreement arises early this weekend with the exact
placement of an upper level North Pacific low that approaches the
eastern Aleutians Fri morning. Models also disagree with placement
of the leading warm front associated with this low. Currently,
the GFS is most aggressive and brings this warm front through
Southcentral Fri night while the EC/NAM solution shows the warm
front stalling out. At this time, the EC/NAM solution is
preferred.

&&

.AVIATION...
The only question for the TAF is whether there will be any stratus
that develops overnight into tomorrow morning. The northerly flow
will persist and this has kept the atmosphere mixed well enough
to keep any significant fog from forming and also kept the stratus
from taking hold this morning. At this time it looks a lot like a
repeat for tomorrow morning with only FEW to SCT cloud coverage
for the stratus.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Cold surface high pressure and offshore flow is the name of the
game for Southcentral and most of the Gulf of Alaska today as a
strong gale force low skirts the southern Gulf. The low will get
closest to the Gulf Coast Thursday afternoon and evening, in
conjunction with a switch to weak northerly flow aloft, so
expecting the best gradient at that time to push slightly stronger
gap winds. Otherwise, weak flow over the Copper Basin will keep
threats for fog and low stratus in place through at least Thursday
and possibly longer.

The next front moves into the Gulf of Alaska Friday which will
bring rain and gale force winds to Kodiak before the front stalls
over the North Gulf. Expecting dry conditions inland into and
possibly through the weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Ridging over southwest Alaska has started to clear out cloud cover
over the area. The ridge axis is pushing east through the area
and as it does the winds will shift to a northeasterly direction.
These northeast winds will last through the night and should be
strong enough to keep fog from forming over the southwest mainland
tonight. This fair weather pattern will last into Friday when a
front moving through the Aleutians will make its way to the
Bristol Bay area. The front will stall there and bring precip to
the Bristol Bay area through Saturday with rain along the coast
and snow further inland.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
A weak low south of the eastern Aleutians is following a track to
the northwest and is bringing rain to the islands as it passes. It
will move into the southern Bering this evening where it will
dissipate. The next system headed this way looks to be much
stronger. It will also come up from the North Pacific bringing
another push of warm air to the area. Its front will make it to
the eastern Aleutians Thursday evening and to the Alaska
Peninsula Friday morning. Strong winds will also be associated
with this system with storm force winds expected on the Pacific
side of the Alaska Peninsula Thursday night into Friday morning.
The main low will not make it into the Bering but will instead
veer off to the east Friday morning where it will diminish as it
tracks toward the Gulf.

&&

.LONG TERM FORECAST (Days 4 through 7)...
The extended period begins Saturday evening with a ridge of high
pressure situated over the Alaska mainland. Near Kodiak Island, a
surface low is beginning to fill as it loses upper-level support
with the jet now racing west to east well south of the state. A
decaying occlusion remains draped across the Gulf east of the low
with a secondary surface low over the Alaska Panhandle. farther
west, conditions remain unsettled as an inverted trough lifts
north across the Bering while a mature low begins to slide east
from Kamchatka. Between the two, a weak ridge lies across the
central Bering. However, low-level moisture and a west-northwest
flow is keeping showers across this part of the chain.

Moving forward through the weekend, the low near Kodiak moves west
to east across the Gulf. Uncertainties in the forecast remain as
they have in previous days, though, as the GFS continues to
strengthen the low and track it farther into the northern Gulf
than the EC, NAM, and Canadian. Given the combination of colder
surface temperatures, the strength of the high pressure over the
mainland interior, and current outflow winds, the GFS is seen as
the outlier in bringing the low and associated occlusion into the
northern Gulf. With the EC favored, this would suggest limited
moisture for southcentral, with precipitation confined to the
coast this weekend. Farther west, the latest GFS/GEFS runs are
also the most aggressive with the placement of the Kamchatka low
and its associated front draped across the Bering. This, too, is
seen as the outlier, with the latest EC runs favored. This would
place the front over the central Bering and Aleutians by Sunday
with a weaker trough along the southwest coast.

Uncertainty within the guidance grows quite a bit moving into
early next week as the GFS continues to erode the high pressure
over the mainland and push the trough over the Bering east. The
EC and to a lesser extent the FV3 amplify the long-wave pattern,
keeping a stout trough over the Bering and ridge in place over
the Alaska mainland. While guidance from the GFS and EC would
keep conditions unsettled across the Bering to the southwest coast
(strong westerly winds and plenty of precipitation), the differences
become more pronounced downstream. To put it differently, the
GFS solutions favor shortwaves pushing across the southwest and
eventually into the northern Gulf and across southcentral
beginning early Monday lingering through midweek. The EC would
favor a drier solution, holding off on the advancement of the
trough through the interior until Tuesday. But the EC also has a
distinct south to north flow east of the AKPEN which would help
advect more moisture and warmer air into Southcentral by mid
week.

Given the issues with the GFS in the short-term, it is difficult
to lend it any credence through the mid-term. Therefore, the
forecast into early next week is weighted toward the EC solution.
However, it is also difficult to buy into the large amplitude
solution of the EC moving beyond Monday. Therefore, after Monday a
compromise between the EC and GFS is favored. This would begin to
erode the high from the south and west late Monday and eventually
bring moisture back into the mainland interior and southern coast
by Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 155. Gale Warning 150 165 170 171 172 173
174 179 180 .

&&

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...TM