Small Craft Advisory 865, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKDT SAT NOV 5 2016

.ANALYSIS AND UPPER LEVELS...
The active North pacific jet stream pattern persists this morning
as another strong low is forming south of the Bering Sea along the
sharp baroclinic zone. A deamplifying upper jet and associated low
is moving into the Southeast Alaska Panhandle with a rapidly
weakening low moving inland and east of the ALCAN border. A series
of weaker mesoscale lows embedded within a broad trough over the
Bering Sea and Western Gulf of Alaska will begin to move northeast
this morning. One of these surface lows is moving inland across
Bristol Bay with a band of enhanced rain and snow showers moving
inland this morning. Near Southcentral, there is another low along
the North Gulf Coast south of Prince William Sound which is
supporting a weak offshore pressure gradient.

&&

.MODEL DISCUSSION...
The models remain in excellent long term synoptic agreement deep
into next week. However, since the main upper jet remains well to
the south, the weaker flow pattern (not strongly forced) means
subtle wave progressions and wave mergers are not as high
confident. Precipitation with the first weak trough moving inland
today and tonight looks to remain rather light, but uncertainty
remains with how far south light snow develops. With that said,
impacts are low and this forecast will continue to take a blended
approach with widespread but light snow forecast for most
locations north of Anchorage. Thereafter, uncertainty grows with
shortwave troughs rotating toward the Gulf Coast as another North
Pacific low lifts northward. The GFS and NAM solutions depict
stronger easterly flow which would largely keep inland locations
on the drier side whereas the ECMWF and Canadian and more bullish
spreading moisture inland Sunday afternoon into Monday. For now a
blended approach was favored which keeps the best precip chances
along the coast and far Eastern Copper Basin.

&&

.AVIATION...
PANC...Snow will develop north of Anchorage early Sat morning.
There is some uncertainty in how far south the light snow will
make it. For now, most likely scenario is the airport will only
see flurries with VFR ceilings. If snow makes it a bit farther
south there could be a brief period of marginal ceiling and vis
sometime between 15z and 21z Sat.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Broad cyclonic flow aloft with combined with multiple weak
surface low pressure centers will continue across much of
Southcentral today. Light snow with relatively minor accumulations
are expected across the Susitna and Matanuska Valleys today
through late this evening. Higher snow amounts are expected along
the Talkeetna Mountains. Flurries generally are expected across
the Anchorage Bowl with some minor accumulations possible at
higher elevations. Light snow is also expected across the Copper
River Basin with a mix along the coasts. Inland areas will dry out
some overnight tonight, however a wave moving in from the east
will bring increased chances of snow to the Copper River Basin
Sunday.

Outflow winds across the eastern Kenai Peninsula will diminish
this morning as pressure gradients relax, but will increase some
again Sunday night. A strong weather front moving north across
the Gulf tonight will bring gales to the southern Gulf tonight
and then spread north through Sunday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A weak low moving inland into Bristol Bay will bring snow showers
to much inland Bristol Bay this morning, mixing with rain along
the coast. Dynamics from this low are quite weak however, so most
areas should receive less than an inch of accumulation before
ending this afternoon. To the north of this low, a shortwave
clipping the Kuskokwim Delta will bring light snow showers
primarily to the lower Kuskokwim Valley and northern Delta.
Moisture from this wave is very low however, so accumulations
should be generally limited to a dusting. Skies throughout the
southwest will then begin to clear this evening in advance of a
North Pacific low approaching the AKpen. While this low and its
main impacts will remain well south of the area, it will bring
clearing skies and offshore flow that will continue through
Sunday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The activity over the Bering today will be focused around the
North Pacific low that is moving just to the south of the
Aleutians. Most of the impacts from this low will come from weak
cold air advection that will develop throughout the Bering. This
system will spread rain showers to the area with northerly winds
generally remaining just below gale force through this evening.
This pattern will break down very quickly however as a front
associated with a Kamchatka low will begin to bring rain and at
least gale force southerly winds to the western Aleutians
beginning Sunday morning. This front will then move into the
central Bering/Aleutians by Monday morning, spreading rain and
gales into those areas.

&&

.LONG TERM FORECAST (Days 3 through 7)...
By Monday morning the next rather large low pressure center will
be entering the western Bering with the associated surface front
stretching across the central Bering and central Aleutians. Well
to the south along this front around 40N, a frontal wave will be
rapidly spinning up and tracking east-northeast along a strong
jet stream. Another deep low will be centered south of the Gulf
with a shortwave trough and secondary surface low rotating around
its northern side and dragging a frontal wave through the Gulf.
The multi-center Gulf low will remain in place with shortwaves
rotating around it through Tuesday.

The low in the western Bering will track southeast crossing the
Aleutians Tuesday and then continue to fill and dissipate Tuesday
night and Wednesday as the low to the south rapidly deepens and
takes over. The southern low will turn northeast and then north
tracking into the southern Gulf as a rather deep low on Wednesday.
The associated frontal system will reach the northern Gulf
Wednesday night bringing rainy and windy conditions to coast
areas. The front will spread inland over Southcentral and
Southwest Alaska Thursday and Friday as the low continues to track
north across the Gulf. Additional storm systems will follow a
similar path into and through the Gulf over the weekend as a more
active storm track enters the Gulf.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 131 132 138 150 155 172 174 175 176 177 178 351
352 411.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...JER