Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 290013
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
413 PM AKDT WED SEP 28 2016
.ANALYSIS AND UPPER LEVELS...
A flat upper level ridge over the northeast Pacific is nudging
into the southeast Bering Sea. An upper level front is over Southcentral
Alaska and moving rapidly east. There is a "cut off" upper level
low south of the central Aleutians that is in the process of
incorporating into the northern stream and moving north. There is
a deep upper low centered near the Kamchatka Peninsula. A strong
trough associated with this low is located to the southwest of the
western Aleutians and moving rapidly east.
The numerical models are in fairly good agreement through the
short term (Friday afternoon). There remain some differences with
a low that moves into the Aleutians Thursday night and Friday. The
NAM is the fastest to bring this into the Bering, while the ECMWF
is the slowest. The preferred solution was the GFS and GEM, which
are in between the NAM and ECMWF. Forecast confidence is near
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level disturbance moves across the Alaska Range tonight
with a southward extension crossing the Gulf waters. This will
bring isolated chances for rain and snow along the mountains to
the north with passing clouds across the Kenai, Copper River and
Gulf. Dry conditions settle across all of Southcentral for
Thursday and Friday as a ridge builds from the North Pacific.
Offshore flow increases tonight as the ridge axis extends north
across Bristol Bay. Gusty conditions through gaps are expected to
develop across Seward and Whittier this evening and then across
outflow areas of the northeastern gulf coast after midnight. Winds
taper off on Friday as the ridge center shifts over the Gulf.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The frontal boundary crossing the mainland will cross the Alaska
Range tonight, as upper level ridging builds in behind it. Inland
area will clear out but some cloud cover will be increasing along
the Alaska Peninsula as well as the Kuskokwim Delta where moisture
advection will promote stratus/patchy fog. Thursday night and
Friday morning winds will increase along the coast ahead of an
approaching front/developing low pressure system. The front will
impact the coast late Friday bringing rain and strong/gusty winds.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Several frontal boundaries and low pressure systems will converge
over the Central Aleutians late tonight and Thursday. The current
front over the Western Aleutians will slowly progress eastward
along with areas of fog as a new low center develops to the south.
A separate front will affect the Central Aleutians/Pribilofs/Unalaska
tonight and tomorrow. As the low pressure system crosses the Chain
into the Bering on Friday, winds will really ramp up to gale
force, even storm force plus through channeled terrain along the
Alaska Peninsula, accompanied by steady rain for much of the area.
.LONG TERM FORECAST (Days 3 through 7)...
Forecast thinking remains largely unchanged for the extended term
beginning Friday night as a Bering Sea front brings a return of
precipitation to the Southwest mainland, while a high amplitude
ridge continues to yield clear skies across Southcentral AK. Model
agreement is slightly improved today regarding the evolution of
the system moving through the Bering late in the week and how that
ultimately impacts the mainland ridge. The front is still expected
to enter the southwest Gulf of AK and then be shunted towards the
southeast by a developing North Pacific wave this weekend, with
high pressure weakening but still remaining in place over
Southcentral AK as the ridge begins to break down. This lends
increasing confidence that the majority of Southcentral AK will
stay mostly dry well into next week, with outflow winds and
freezing overnight low temperatures remaining the primary forecast
concerns. Meanwhile, the Bering will remain in a much more active
pattern as various waves continue to rotate around the the
periphery of the deep Siberian low, with a weak disturbance on
Sunday followed by potentially stronger systems on Monday and
again towards the middle of next week.
MARINE...Gales 165 170 171 172 173 174 175 176 179 181 185 411 412
SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML