Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 280047
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKDT THU OCT 27 2016
.ANALYSIS AND UPPER LEVELS...
Satellite imagery this morning shows a low south of Kodiak island
spinning slowly to the southeast. the associated low level jet to
the north of this low has been bringing steady rainfall and gusty
winds across Kodiak Island overnight. Meanwhile to the west,
satellite imagery indicates a deep fetch of moisture being pushed
north across the Central Aleutians. A surface front sits beneath
this upper jet and is slowly intensifying and bringing gusty winds
to the central Aleutians. Meanwhile clear skies are building in across
mainland Alaska as the Gulf low pushes south and high pressure
becomes temporarily re-established.
Models are in generally good agreement today as the front across
the central Bering continues to intensify slightly and push
towards Bristol Bay. There is still some difference however on
the manifestation of a triple point low along this baroclinic zone
as it approaches Bristol Bay. This has important implications for
the intensity of gusts across Bristol Bay and coastal portions of
the Kuskokwim Delta, so a blend middle solution was chosen.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The low south of Kodiak will continue to move off to the east this
evening, taking with it the rain and wind currently impacting
Kodiak Island. This will also keep the offshore dry flow in place
over Southcentral Alaska through Friday.
The next storm system to impact the southern mainland is a storm
currently over the western Bering Sea. The front associated with
this low will be moving the the Bering Sea coast by tomorrow
afternoon. The front begins to break down through Friday night as
it moves into the Kodiak Island to Cook Inlet region. The overall
result will be increasing temperatures over the southern mainland
with increasing chances for rain and snow. The Copper River Basin
will be the last to respond to the warming and we have slowed the
increasing temperature trend until Saturday. Coastal locations
will see wet windy conditions beginning late Friday night across
Kodiak island spreading to Prince William Saturday.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A strong frontal system approaching from the west will bring
increasing south to southeasterly winds to Southwest Alaska late
tonight through Friday. These strong winds accompanied by heavy
rain will reach the Alaska Peninsula and Kuskokwim Delta Friday
morning and spread east into the Bristol Bay area through the
afternoon. At the moment it is looking like sustained winds will
reach 45 to 60 mph in exposed coastal locations with gusts up to
70 mph. However much depends on how how rapidly the frontal wave
develops Friday and how deep the resulting surface low is as lifts
north across the Eastern Bering. Model uncertainty remains
moderate regarding both of these factors and whether or not the
low will be deepening at a great enough rate to overcome the warm
air advection affects and allow the stronger winds to mix down.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The frontal system currently pushing into the central Aleutians
will strengthen rapidly tonight as it pushes east to the Eastern
Aleutians. A developing frontal wave will lift north bringing storm
force south to southeasterly winds to portions of the eastern
Bering and Southwest Alaska coastal waters late tonight through
Friday. The vertically stacked parent low in the western Bering
will track to the north then northwest...moving into Siberia
Friday night and Saturday. The next rather strong North Pacific surface
low will rapidly track in from the west to the south of the Aleutians
.LONG TERM FORECAST (Days 3 through 7)...
Beginning Sat night an upper ridge over the eastern half of
mainland AK will reside along the eastern flank of a low that
covers all of the Aleutians, Bering, Kamchatka and western AK. A
decaying front will persist over the Alaska and Aleutian
ranges. The next wave moving along the southern quadrant of this
upper low will produce a surface low that crosses the central
Aleutians Sat night. Models are in very good agreement with this
development. Differences with the detail of its track through the
Bering, however, are caused by different representations of the
mainland ridge as it noses into the northern Bering.
For now the forecast is closer to the EC in that it builds the
high into the northern Bering, which causes the low to head west.
Confidence not high with this trajectory since it depends on
ridge building which other models downplay. Given this solution,
by Tue the low reaches the northwestern Bering where it spins
through Thu. In the meantime the front over the mainland slowly
decays, and the next wave moving around the upper low brings a
surface low into the southern Gulf on Thu.
The Bering and Aleutians can expect significant rainfall with the
low and associated front into Tue, with Gales and Storms through
Tue diminishing to Small Crafts by midweek. Rain and wind will
also affect southwest AK through Tue before diminishing.
Southcentral will receive rain, initially from the decaying front,
and then beginning on Mon from a front associated with the Bering
low. Much of the precipitation from these events will be on
windward sides of mountain ranges.
MARINE...Storms 155 160 165 172 180 181 185 414. Gales 130 150
170 171 173 174 175 176 177 178 179 411 412 413.
SYNOPSIS AND MODEL DISCUSSION...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR