Flood in Alaska, October 9 to 14, 2016

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
355 PM AKDT SAT OCT 8 2016

.ANALYSIS AND UPPER LEVELS...
An omega block remains in place over Alaska this afternoon. An
amplified upper-level ridge of high pressure is parked over
Mainland Alaska while low pressure dominates the Bering Sea and
Southeast Alaska. The occluded low over the Bering is gradually
filling as it tracks northwestward towards the eastern Russian
coast. As the low continues to weaken, gale force winds wrapping
around the system over the western Bering are diminishing
throughout the day. An associated front stretches from eastern
Siberia southeastward along the southwest Alaska coast and across
the Alaska Peninsula, bringing storm force winds and rain to these
areas. Satellite imagery shows a wave developing along the front
south of the Alaska Peninsula, which is aiding in the intensification
of winds and rain along the front.

Further east, much quieter weather continues over the Southcentral
Mainland under high pressure. Clear skies and calm to light winds
are allowing for strong radiational cooling at night, and the
lengthening nights are making it harder for daytime temperatures
to recover each day. The result has been a cooling trend with the
coldest temperatures of the season being reported over Southcentral
over the past couple of days.

&&

.MODEL DISCUSSION...
Models are in good agreement on synoptic features across the Gulf
and Southcentral Alaska through the short-term forecast period
(Monday Afternoon). Out west, models are in fairly good agreement
through Sun afternoon with the weakening Bering Sea storm tonight
and a developing Western Pacific low which moves to near the
western Aleutians Sun afternoon. Models diverge quickly after this
and continue in poor agreement into Monday. The NAM/GFS hold a
fairly strong low near the Central Aleutians into Monday while the
ECMWF/Canadian move the main low center well south of the Eastern
Aleutians. It seems reasonable with the strong zonal flow
developing over the North Pacific that there will likely be a
fairly significant triple point development south of the Eastern
Aleutians/western Alaska Peninsula and a weakening parent low
holding near the Central Aleutians.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
Ridging will remain over Southcentral Alaska early into the week
but it will diminish and push off to the southeast Sunday before
rebuilding back over the area Monday. As it weakens it will give
way to the front near Kodiak allowing it to push in over the
island bringing rain to the area and cloud cover to portions of
Southcentral Alaska. However, as the ridge rebuilds it will push
the weakening front back to the southwest and cause gap flow winds
to increase in east to west oriented gaps on Monday. On Tuesday
another front will move in over Kodiak Island but will be held up
from further advancement by the ridge.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A frontal system along the Southwest Alaska coast stretching from
the Kuskokwim Delta coast across Bristol Bay and the Alaska
Peninsula will begin shifting east tonight as several shortwaves
rotate around the large upper low over the Bering. The front
however will not make it very far inland and shear apart Sunday as
it hits the large blocking ridge over Mainland Alaska. The tight
easterly pressure gradient currently over Southwest Alaska will
weaken Sunday as the front falls apart allowing the strong easterly
winds to slacken somewhat and turn more southeasterly. Southeast
winds will increase again on Monday as a developing frontal wave
lifts north towards the Alaska Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The very large vertically stacked low over the Bering will
continue to gradually fill as it tracks northwest Tonight and
Sunday. The next developing low coming in from the west-southwest
will reach the Aleutian chain around the 180 longitude late
Sunday then move northeast before stalling in the southern Bering
just north of the Central Aleutians on Monday. A triple point
low/frontal wave developing to the south along the north side of
the strong west to east running jet centered around 45N will take
over as the next next feature of significance, although models
struggle with its strength and track. Some solutions have it
phasing with a frontal wave developing along the old front south
of the Alaska Peninsula and lifting it north while others keep it
as a strong independent system further south tracking rapidly east
along the jet. Given the strength of the jet stream tend to favor
the stronger and further south solutions, although do also think
the other two features (the low in the Bering and wave lifting
north to the Alaska Peninsula) will exist and be significant
players as well.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The high latitude omega blocking pattern will quickly break down
on Wednesday as the trough over the Bering Sea/North Pacific
amplifies significantly. The amplification will be caused by a
strengthening jet stream over the North Pacific that will allow
more cold air over Russia to dive down over the Bering Sea. With
increased dynamics of the developing jet stream (and resultant jet
streak), a strong area of low pressure is expected to push across
the Aleutian Islands and Alaska Peninsula Tuesday and Wednesday
before ultimately moving into the Gulf of Alaska.

The Bering Sea will remain quite active over the next 7 days due
to the strengthening upper level trough and numerous disturbances
pushing through the region. Over the Alaska mainland, the ridge
that has been over the region for the past several days will get
pinched off and drift northward toward the arctic as the trough
over the Bering amplifies. This will allow rainfall to return to
Kodiak Island and the gulf coast of Alaska next week but offshore
flow should keep much of interior Alaska on the dry side.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning 173 174 175.
		 Gale Warning 130 132 150 160 170 172 176 177 178 185.

&&

SYNOPSIS AND MODEL DISCUSSION...RD/BC
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...MC