Gale Warning 578, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
407 AM AKDT SUN OCT 2 2016

.ANALYSIS AND UPPER LEVELS...
The closed upper level low remains over the Kamchatka Peninsula
with an associated trough extending through the northern Bering
into the Southwest Alaska region. While, a weak triple-point low
is forming east of Kodiak Island this morning. Look for this
system to track eastward as the 120-knot zonal jet stream located
south of the Gulf of Alaska continues to move eastward. The
satellite imagery has the bulk of the moisture streaming from the
Gulf northward through Southcentral region into the North Slope
territory. The Bering/Aleutians is under the influence of
southwesterly flow with a showery weather regime as a weather
front pushed onshore through the Southwest Alaska area this
morning. These synoptic features coincide with the radar imagery
showing widespread rain throughout the aforementioned region.
The northern Gulf coastal communities are getting the heaviest
rainfall accompanied by onshore flow.

&&

.MODEL DISCUSSION...
The models are in decent agreement as the low tracks from the
Bering into the Eastern Russia region, and with the developing
low located east of Kodiak Island. The GFS was the preferred model
of choice due to the consistency. By Monday the models begin to
struggle with a low pressure system dropping off the Kamchatka
Peninsula, and tracking into the Western Aleutians. The ECMWF
remains the outlier with a faster system, and the NAM lagging
behind. Meanwhile, the Gulf has the triple-point low tracking
eastward, and dissipating heading into this upcoming week. By the
midweek time frame the models struggle with the strength, and
timing with a North Pacific Low as it tracks into the Western
Aleutians/Bering Sea. Therefore, the forecast confidence starts
out above average, but weakens due to the discrepancies with the
next system as it enters the Bering by Wednesday.

&&

.AVIATION...
PANC...Ceilings will gradually lower as downslope flow gradually
becomes weaker and transitions to a more northerly flow aloft later
today. However, with continued low-level moisture and below-
mountaintop winds remaining weak we are likely to see lowering
ceilings to MVFR especially along the Chugach Range, while VFR
conditions are still the most likely scenario at the airport
itself, though confidence is low at this point.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The primary upper level short-wave and surface low just east of
Kodiak this morning will exit across the Gulf today, leaving
behind weak and diffuse flow across Southcentral. With numerous
weak embedded waves moving through a very moist environment with
a little bit of low level instability, expect areas of light
rain or showers will persist, but it is very difficult to
pinpoint exactly where this will occur. Thus have used a
broad-brush approach to the precip forecast.

Deep northerly (offshore) flow will develop tonight and
strengthen Monday through Monday night as a ridge builds upstream
over Southwest Alaska. This will result in a gradual drying trend.
Surface flow will still be quite weak Tonight, so expect fog may
become a problem, depending on how quickly clouds begin to break
up. For now, have stuck with patchy fog, but there is potential
for more widespread fog to develop. As flow strengthens Monday and
Monday Night a weak outflow event will develop along the Gulf
Coast and Prince William Sound.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

A weakening frontal boundary remains draped across Southwest
Alaska this morning with a definitive back edge of precipitation
now apparent on the PABC and PAKC 88-D's. Rainfall will continue
to taper off from west to east throughout the day as the front
continues to push inland and weaken. The majority of the rainfall
should taper off by this evening but scattered showers will remain
possible throughout Sunday and much of Monday as colder air moves
in aloft and a conditionally unstable environment sets up. Some
gusty winds will continue through gaps in the Alaska and Aleutian
Ranges this morning but should taper down significantly after
sunrise as the gradient becomes less favorable to support gusty
winds. Overall, a much quieter and calmer period of weather is to
be expected for the next several days.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A weak front currently draped across the western Bering Sea will
continue to move east throughout the day while gradually weakening.
A nice core of 30- to 35-kt winds will impact the southern Bering
Sea near Adak and Atka this morning but winds will weaken by the
afternoon as the front begins to shear apart. By the time this
front falls apart, another decent front will quickly move into the
western Bering Sea tonight as a strengthening low pressure system
moves eastward off the Kamchatka Peninsula. Another shot at gale-force
winds and moderate to heavy rainfall will be common across the
western Bering Sea on Monday in response to this front.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Looking into early next week there has been little change in the
overall forecast reasoning since yesterday. A low departing the
Gulf on Monday will bring weak ridging to the southern mainland,
providing most of the area with a period of benign weather that
should persist into Wednesday. The pattern over the Bering and
Aleutians will be much different as a very active and progressive
pattern will setup beginning Monday and possibly persisting into
the end of next week as a series of developing systems pass
through the region. Each one of these systems will likely bring
rain and at least gale force winds to the western-central
Aleutians and Bering. Starting Wednesday, the models have all
backed off significantly on the development of an omega block that
looked to setup over the mainland. As a result, the forecast for
Thursday and afterwards looks much more active, especially for the
southwest mainland and the Gulf as the upper trough over the
Bering begins to approach the southwest coast. This trend would
then continue into next weekend as all guidance now indicates that
a broad trough will setup throughout the forecast area, bringing
at least chance of rain to most areas.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales...130-132 150 177 178 185 352 411 413.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
AVIATION...CC
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...DEK