Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 280017
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
417 PM AKDT WED JUL 27 2016
.ANALYSIS AND UPPER LEVELS...
A fairly elongated meridional pattern is set up across Alaska. The
domain is dominated by a ridge over the western Bering and a deep
trough over the western half of the state. Under the ridge, a
surface high is located well southwest of Shemya near 45N. A
surface low is embedded within the trough and tracking through the
northern Gulf of AK. This low is the primary weather maker today.
It is currently spinning some showers from the Gulf Coast up
through the Susitna Valley. The heavier stratiform rain is
stretched out from Valdez through Kodiak Island. This rain should
make its way inland later this evening as the low tracks slowly to
the northeast. There has been enough sunshine early today to
create some inland instability. This has led to some heavier
showers popping up over the Talkeetna Mountains. Another weaker
low within the trough is spinning over the YK-Delta. This is
helping to keep clouds and light rain across much of that area.
Finally, over the Bering, high pressure is once again leading to
widespread marine stratus and some patchy fog.
Most of the upper level jet energy is located in the SE Gulf
heading towards SE AK. There is a 110 kt portion of the Polar
Front Jet over the NW portion of AK. This is helping to support
an Arctic low, which will play a big role in the mid-long term
The American models have been leading the way with the low in the
Gulf. The Canadian and EC initialized too weak, especially with
the gale-force winds in the barrier jet region. The NAM shows some
downsloping SE winds continuing over the Cook Inlet region through
the day until a more organized upper level wave brings in some
substantial showers late this evening. Models vary wildly in
handling this precipitation as some pull the low away faster and
actually keep most inland areas dry tonight. So while forecast
confidence is not high, this package leaned towards the NAM.
There is good model agreement that a shortwave trough will move
over the Alaska Range from the NW very early Fri. This trough
should be enough to push the pesky Gulf low to the east of our
area. It will bring some light precipitation to areas from the
Kenai Mountains up through the Talkeetna mountains. The best
chance for precipitation will be on west facing slopes. After this
clears through the area by Fri afternoon, there is increasing
confidence that dry zonal flow will set up at least for the start
of the weekend. See the Long Term Discussion for more details on
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
a potent upper level low and the multiple short-waves associated
with it will continue tracking northward into the Northern Gulf by
late tonight, along with a deepening surface low out ahead of the
upper low center. This is a very strong and dynamic system which
will produce a lot of rain and some gusty winds, mainly for the
areas surrounding the gulf coast. Conditions will continue to
deteriorate along the Gulf coast and Kodiak Island this evening,
while inland areas will see increasing showers as the area of
upper diffluence on the leading edge of the system moves overhead
tonight. The low will become vertically stacked tonight causing it
to stall over the northwest Gulf. A jet streak on the east side of
the low will drive frontal precip and upper short-waves inland, so
expect some rain to fall just about everywhere tonight and into
Thursday morning. With some increased instability behind the
surface occlusion, expect some isolated thunderstorms to develop
tonight over the Northern Gulf. Even if thunderstorms do not
develop, expect very heavy downpours and gusty winds in showers.
An Arctic trough dropping into western Alaska on Thursday will
help kick the low over the Gulf eastward. After a rainy/showery
start to Thursday morning, this will lead to improving conditions
across much of Southcentral and the Gulf during the day Thursday.
The trough will reach Southcentral by Thursday Night, bringing
another shot of rain to the region. With west to southwest flow
ahead of it, rain will then become focused along the west side of
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The mainland is between weather systems for the next two days but
showers remain possible, especially for the Kuskokwim Valley.
Scattered rain shower activity will subside this evening through
the overnight hours. Thursday will see partial clearing of clouds
in the morning before another round of afternoon showers. Most of
these showers will be in the Kuskokwim Valley but there is a
chance to see some over the rest of the mainland, especially along
the western slopes of the Kilbucks, and Alaska/Aleutian ranges.
Southwesterly flow from the surface to the upper levels takes hold
on friday bringing a return of marine layer stratus to most areas
of the mainland.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Marine layer stratus and fog dominates the Bering Sea. There will
be a diurnal pulsing to the fog/stratus with general lifting and
improving visibility during the day and deteriorating conditions
at night. The western Bering will remain pretty socked in
regardless of time. Winds will remain generally light with
southwesterly flow becoming established by Friday.
.LONG TERM FORECAST (Days 3 through 7)...
A zonal pattern starts off the mid term with predominantly
westerly flow and showery precipitation. Moving into Saturday a
trough digs down from the north pushing through Southwest Alaska
through Sunday. This trough will bring more rain to Southwest
and Southcentral Alaska. However, there are some questions on how
much rain for Southcentral. Guidance is trending to push more of
the energy south helping to form a closed low near the Alaska
Peninsula or Kodiak Island. Previous solutions kept the trough
more intact with the bulk of the energy staying to the north.
What this means is that rain looks to be widespread across
Southcentral Alaska on Sunday. But the position of the low is
still in question and this could lead to varying times and amounts
of rain. Then, moving into next week, high pressure will build in
along the west coast and help clear out the rain bringing back
SYNOPSIS AND MODEL DISCUSSION...mo
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ml