Small Craft Advisory 633, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 AM AKDT Fri Aug 17 2018

.ANALYSIS AND UPPER LEVELS...
The longwave pattern features a deep trough covering most of
mainland Alaska and the Aleutians. There is a dome of high
pressure over the Central Bering. There are numerous weak
shortwaves across Southcentral, the interior of Alaska and over
Southwest Alaska. The most organized disturbances are near the
Eastern Aleutians and south of the chain. The radars on Kenai and
Middleton Island continue to locate areas of light precipitation
again this morning over portions of South Central and the northern
Gulf Of Alaska.

&&

.MODEL DISCUSSION...
The global models are in good agreement with the major synoptic
features through Sunday. There are some minor differences in how
they handle the precipitation. Beyond Sunday, the GFS and the
ECMWF look very similar with the ridge axis over the Eastern Gulf
Of Alaska and into the Interior. However, the same two models are
wobbling over the evolution of the deepening low that is southwest
of Kodiak. The global models are also out of sync in the Bering
and the tropical energy in the West Pacific. There is some sense
of uncertainty beyond 48 hrs. Expect forecast
adjustments/amendments for Monday and beyond.

&&

.AVIATION...
PANC...VFR conditions will persist. There are some showers on the
Kenai radar again this morning in the vicinity of Anchorage. Added
VCSH to the TAF.

&&

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

Southcentral Alaska is in the break between systems, but in August
that does not necessarily mean that the weather will be great. A
short wave along the Alaska Range is keeping some showers in that
region. Those showers should slowly taper off as upper level
ridging moves in from the south. This ridging will bring some
partial clearing to parts of the area today, but the next front
is moving in from the Pacific and will bring more rain to Kodiak
Island beginning this evening.

The low associated with the front is moving slowly so its progression
was slowed up a little in the latest forecast. Gales will develop
in the marine areas along the Gulf side of the Kenai Peninsula as
well as around the Kodiak Island waters tonight into Saturday with
the tightening pressure gradient. While winds will also increase
through Turnagain Arm, they will mostly turn to the left and
down-Inlet Saturday and Sunday due to the low remaining well to
the southwest of Kodiak.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (through Sunday)... A
fairly benign day is in store for the mainland. Lingering moisture
and light winds will make for patchy fog early this morning,
especially where clouds clear overnight. Otherwise, some breaks of
clouds will make for a partially sunny day with no chance for
precipitation. Late tonight, a front from the Pacific moves over
the area. The main effect will be an increase in southeasterly
winds in the Bristol Bay region, however, some light rain will
also accompany the front where downslope drying is not occurring.
On Sunday, the front washes out overhead, leaving much of the
mainland in cyclonic flow which will bring at least a chance for
rain showers. Expect clouds to and winds to increase late tonight
and temperatures to remain near normal for this time of year.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (through Sunday)...
Several fronts will move into the region. First, a north Pacific
storm system will swing a solid gale-force front over the Alaska
Peninsula this afternoon and evening. Along with widespread rain,
some gusts into the 50-60 knot range are expected along the front
through Saturday. The front washes out pretty quickly on Sunday as
the responsible system weakens well south of the Peninsula. A
secondary front will enter the western Bering Sea on Saturday
carrying a north/south orientation and southerly winds.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term, beginning Saturday night, starts with ridging over
the eastern Gulf that extends over the southern mainland and
ridging over the western Aleutians and Bering. In between the two
ridges is a low centered south of the Alaska Peninsula with a
front pushing in over southwest Alaska. The eastern ridge is
holding strong which will stall the front over the southern
mainland bringing rain to the area into mid next week. The western
ridge will be breaking down which will allow for another system to
move into the western Bering early next week.

Mid next week the models diverge on what happens with the low in
the Bering. The GFS keeps the low over the western Bering which
would have little impact on the southern mainland. However, the EC
has the low moving into the eastern Bering which would bring
widespread rain to the southern mainland. Because of these
differences the ensembles were preferred.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...GALE 130 131 132 138 352 150 155 160 165 170 171 172 173
174 180 414.

&&

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