FXAK68 PAFC 261313
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
513 AM AKDT SUN JUN 26 2016
.ANALYSIS AND UPPER LEVELS...
The upper level trough encompassing much of the Alaska mainland
has remained in place through the overnight hours. Rain showers
and a few thunderstorms continued through the early morning hours
across the western half of the Kuskokwim Delta and the Bristol Bay
area. Thunderstorm activity has all but diminished this morning with
the loss of daytime instability that developed on Saturday but
lingering showers continue to move from north to south across
Southwest Alaska. The massive ridge that currently encompasses
the majority of the Bering Sea continues to slowly build eastward
which has kept area from Bethel west on the dry side. The last few
faint glimpses of visible satellite before the sun set showed a
large area (extending from Shemya all the way east to Cold Bay and
north to Saint Matthew Island) of marine stratus and fog trapped
under the high pressure. Very little change in this feature has
been noted throughout the day as sounding from PASY and PACB show
a well defined subsidence inversion.
Looking further west toward Shemya...the next system that will
impact Alaska has begun to take shape as a weak low has begun to
develop along the triple point of a frontal boundary south of the
Kamchatka Peninsula. This front has been make steady eastward
progress overnight and is currently just to the west of Shemya/Attu.
Models remain in very good agreement once again which is no
surprise because the overall synoptic pattern has not changed
much in the past 24 hours. The general trend of the east/southeast
displacement of the ridge over the Bering Sea looks to be well
progged but there are a few minor timing issues. This relates back
to a developing area of low pressure to the west of Shemya. Based
on the development of this low and the progression of the sfc
front, a change to speed up or slow down the displacement could
be seen in the coming days. The NAM has been doing a better job
than the GFS with convection although some of the parameters have
some convective feedback so a trend toward the NAM for thunderstorm
placement and probabilities was utilized across southwest Alaska.
For the overall forecast, a blend toward the America guidance
(NAM/GFS) was utilized once again with an above average confidence.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The low in the Gulf of Alaska continues to support a showery
weather pattern across the mainland. A well-developed easterly
wave is currently bringing steady showers to the western Copper
River Basin, Matanuska Valley and Anchorage Bowl. Showers are
expected to linger but slowly diminish throughout the day as the
upper level wave slowly weakens and slides to the southwest.
Currently instability is expected to be relatively low, and no
lightning strikes are anticipated across southcentral today.
While showers will generally diminish through the overnight hours,
a more well developed wave will push through the region on Monday
afternoon and generate another round of steady showers Monday
afternoon into Monday night.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper disturbance moving over a moist airmass will bring
another round of showers and thunderstorms to the Kuskokwim
Valley and adjacent mountains today. On Sunday the arrival of a
front from the northern Bering will again bring showers and
thunderstorms to the same area.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Northwest flow across the eastern half of the Bering and Aleutians
will continue today, with light rain and areas of fog, mainly
along the Bering coast. This will continue on Monday. The western
half of the area will come under the influence of a pair of fronts
from a north Pacific low. These will bring spread rain and some
fog to that portion of the forecast area, as the fronts reach the
central Bering and Aleutians Monday afternoon and then stall.
.LONG TERM FORECAST (Days 3 through 7)...
Monday afternoon brings a continuation of the current pattern and
conditions into the late week. Mostly cloudy conditions with a few
breaks of sun will prevail. The north gulf coast will see the
brunt of showers in this pattern, while scattered showers will
build on elevated terrain in the afternoon/evening hours around
the rest of Southcentral Alaska. Tuesday will bring nearly the
same conditions with a bit more coverage of rain showers along the
Gulf Coast, but coverage will increase almost everywhere on
Wednesday as the gulf low begins to move overhead. Thursday is
when the gulf system really starts to influence the area, making
widespread rain likely. Toward late week the initial system moves
to the west and weakens while another takes its place in the gulf.
Temperatures will generally be in the 60s inland with 50s along
the coast with light winds, except for diurnally forced gap winds.
SYNOPSIS AND MODEL DISCUSSION...MC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS