Small Craft Advisory 546, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKDT Thu Jul 20 2017

.ANALYSIS AND UPPER LEVELS...
There is an upper level low in the southwest Gulf of Alaska that
is moving towards the southeast. An associated surface low is
southeast of Kodiak Island. The front is stretched east-to-west
across the northern Gulf into Kodiak Island. An upper level high
is over most of the Bering sea, and building into southern Alaska
from the west. Only a few showers remain over the mainland of
southern Alaska this ridge builds in. There is an upper level low
over the central Aleutians that is moving rapidly southeast.

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.MODEL DISCUSSION...
The numerical models are in good agreement today. The GFS and NAM
were mostly used for the afternoon forecast package. Forecast
confidence is higher than normal.

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.AVIATION...
PANC...VFR conditions will persist. Some breezy southeast winds
are possible this evening, otherwise winds will be light.

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.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Conditions will continue to improve across much of Southcentral
Alaska this evening, as the front over the northern Gulf weakens
and retreats southward over the central Gulf by Friday morning.
Residual cloud cover will linger over much of the area through
the overnight hours tonight, before an upper level ridge builds
into the region and supports gradually clearing skies and warming
temperatures Friday. Some diurnal showers could form Friday
afternoon/evening along the Alaska Range and Talkeetna Mountains,
but generally rainfall will be limited. By Saturday however,
mostly clear and warmer conditions could aide in the development
of some isolated thunderstorms in the afternoon/evening along the
northeast Alaska Range and Talkeetna mountains.

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.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
With the ridge continuing its march inland, upper level heights
will build and expect a distinct warming trend. Residual mid level
moisture will fuel afternoon/evening convection over the Western
Alaska Range and Lower Kuskokwim River. Along the coast,
inversions will hold up. Patchy fog is expected to materialize at
Nunivak Island and push eastward.

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.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The synoptic pattern features a high amplitude ridge over the
Bering Sea and a low over Adak. As time elapses, the low will
rapidly push southeast. The high will be the dominate feature this
forecast period. Stable conditions anticipated as the warm air
moves over the cold water. Expect mild dry conditions with areas
of marine stratus and fog.

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.LONG TERM FORECAST (Days 3 through 7)...

At the start of next week the synoptic set up for the southern
mainland will be under the influence of troughs moving inland from
the Bering Strait. Models are honing in on a similar solution for
Monday and Tuesday, bringing a significant fast paced shortwave
across the Southwest coast early Monday. Southwesterly flow at
the lower levels will keep a moist profile near the surface. This
moisture combined with ample diurnal heating will prime the
environment for showers to readily develop along wave.
Thunderstorms are also a possibility, however the timing of the
wave is still uncertain so will leave mention out of the forecast
until there is better model run consistency. This first wave
traverses across all of Southcentral by early Tuesday. This first
system paves the way for the next wave which arrives along the
southwest coast early Tuesday. This wave progresses just as quick
across the region, although it looks like it dives more to the
south.

To the west across the Bering and Aleutians, the ridge pattern
over the western water amplifies into the middle of next week
keeping a drier pattern across the western Bering/Aleutians with
areas of fog developing under a stable air mass. The eastern and
central Bering will see a mix of weather as this area stays under
the influence of both the upper low and ridge.

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.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 138.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
LONG TERM...KH