Small Craft Advisory 553, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
422 PM AKDT SUN JUL 10 2016

.ANALYSIS AND UPPER LEVELS...
There is a sharp north-south oriented upper level trough over
western Alaska. This trough is associated with a deep low over
the Arctic Ocean north of Siberia. There is a band of moisture and
precipitation ahead (east) of this trough. South central Alaska is
in a "col" between this trough and a low off the coast of the
Alaskan Panhandle. Some diurnally enhanced convection is within
this col. There is a large and somewhat flat ridge over the
Bering Sea. A weak upper low is "inside" this ridge over the
western Bering. There is also an upper low south of the central
Aleutians.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement for the general
synoptic situation. There are some differences in the details,
especially in the handling of minor vort-maxes in the western
Alaska trough and in moisture/convection. The Nam seems to be a
little out of consensus by 00z Tuesday and was not preferred.
Forecast confidence is near to slightly above normal.

&&

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

As the upper low dives south tonight, the eastern flank will
trigger a few evening thunderstorms...mainly over the susitna
valley and copper river basin. As the low continues its dive into
Tue, the upper flow will become more easterly. This will allow the
thermal ridge to push across the Copper River Basin and Susitna
Valley. As waves move through this moisture rich region,
afternoon and evening thunderstorms will develop Mon and Tue.
Although showers are expected south of this area, a few
thunderstorms are also possible for the Matanuska valley.

&&

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

A few lingering showers are expected to continue across the
eastern half of the Kuskokwim Valley through Monday morning as
rainfall upslopes along the Alaska Range. Otherwise, clearing
skies and warmer temperatures are on tap for the beginning of the
week as high pressure builds across the region from the Bering
Sea. It appears, however, that this dry period will be somewhat
short-lived as the lingering upper level trough over portions of
Southwest and Southcentral Alaska forms into a closed low near
Bristol Bay Tuesday afternoon. This will bring rain chances back
to the Bristol Bay area but the Kuskokwim Delta and Valley should
still remain on the dry side. Following the departure of this
upper low on Wednesday, temperatures are expected to warm into the
mid to upper 70s for many locations with the return of thunderstorms
possible Wednesday afternoon.

&&

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

Once again it appears fog will be the primary challenge through
the forecast period as surface high pressure remains thoroughly
entrenched. A weak shortwave residing on the northern periphery of
the upper level ridge will push south into the central and
eastern Bering Sea Monday and Tuesday and bring a chance of rain
to the area. However, with forecast soundings and current
soundings all showing a significant subsidence inversion (see
PASY) near the surface, the weak wave isn't expected to fully mix
out the fog although it may briefly improve visibilities. The
western and central Aleutians will likely see widespread visibilities
drop to 1/4 mile again tonight with no change in the synoptic
pattern but the Pribilof Islands should stay at one mile or greater.

&&

.LONG TERM FORECAST (Days 3 through 7)...
High pressure will continue to build in over the Western Bering
into Thursday with ridging from the main high expanding out over
mainland Alaska. This will keep fair conditions over the southern
mainland through the remainder of the week with afternoon
temperatures reaching the mid to upper 70s. These high
temperatures combined with the ridge not being all that strong
will lead to afternoon showers, particularly over the mountains.
On Saturday, the models are coming into better agreement on a
trough swinging down from the north. However, there is still
disagreement on how strong in will be and thus how much rain it
will bring to the southern mainland.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

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