Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 151220
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
420 AM AKDT Sun Oct 15 2017

.ANALYSIS AND UPPER LEVELS...
The latest satellite images depicts a series of lows south of the
Aleutians and into southeast AK. The jet stream which is steering
theses lows remains zonal with a 150+ kt core. Over the Gulf of
Alaska, the remnants of an upper level circulation continue to
churn with a surface low near Yakutat. Meanwhile, the latest
ASCAT pass depicts a new low of interest off the northeast coast
of Russia.

&&

.MODEL DISCUSSION...

The GFS and the NAM initialized well pinging into the lows near SE
Alaska and NE Russia. Through 24 hrs, the models are in lock step
with the major synoptic features. Beyond that time frame, the
solutions start to diverge with the timing of the next low to
impact the Aleutians and the frontal structure. But all of the
models depict the transition from zonal to meridional flow as the
ridge/trough couplet over the north Pacific evolves.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Clouds are diminishing steadily this morning across the southern
mainland in response to strengthening high pressure to our west.
This has allowed temperatures to drop to near or just a few
degrees below our morning low temperatures from yesterday. Some
localized fog has formed in the Matanuska Valley, but this should
diminish quickly this morning shortly after sunrise. A very nice
day with occasional high clouds will unfold for much of the area.
The exception to this sunshine will be eastern sections of the
Copper River Basin, where clouds will persist for much of the day
associated with the storm centered near Yakutat.

Temperatures tonight will again drop to new seasonal lows for many
locations as cold air and mostly clear skies continue to move
into the area. Some showers may try to move into the Cordova area
as the storm near Yakutat breaks apart and general instability
spreads westward, but nothing significant is expected in the way
of precipitation.

For the start of the week, cold and mostly clear conditions will
continue, though there is some uncertainty with how much mid- and
high- level cloudiness moves into the population centers as a
large and diffuse upper level low begins to set up shop over
northern Cook Inlet. For now, have leaned toward the
clearer/sunnier end of things in the morning forecast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

A decaying area of low pressure over the southern portions of the
Gulf of Anadyr will continue to bring onshore flow that will usher
in moisture and slightly above normal temperatures to the region.
Colder air filtering in aloft will create some steep low-level
lapse rates that will interact with the moisture to create
scattered showers all across Southwest Alaska. Onshore flow will
weaken Monday night which will allow temperatures to slowly cool
off to more normal temperatures midweek while shower activity
diminishes with a drier pattern engulfing the region.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

The Bering Sea will continue to see an active period of weather
thanks to the placement of the arctic jet which is situated along
the Aleutian Islands. Due to the location of the jet, any
shortwave propagating the longwave pattern will spin up across
the northern Pacific Ocean or Southern Bering Sea. Saying this,
two disturbances are slated to move across the southern Bering Sea
through the day 3 period (Tuesday). The first is an open wave
with a weak surface reflection that is currently located just to
the west of Adak. This wave will intensity into a closed low this
afternoon with 20 to 30 kt winds and some light to moderate
rainfall being observed across the central and eastern Aleutians.
The more potent low will move near Shemya late Sunday night around
992 mb and will strengthen as it moves across the Aleutian Chain
through Tuesday. At this time, it looks like some storm force
winds will be possible south of Adak Monday night. There does
appear that there will be some subtropical influences so there
could be some fairly heavy rainfall that falls along the Aleutians
on Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The mid and long term forecast, starting Monday night, will have
a storm track south of mainland Alaska. This setup will have a
series of lows moving across the Aleutians but staying south of
the mainland. There is somewhat decent agreement amongst the
models with these lows but exact placement and intensity is still
a struggle. For the southern mainland, this pattern would leave
the area in primarily cold, dry outflow for much of the week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...GALE 413...175-178.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...AD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...DK


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