Small Craft Advisory 591, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
423 AM AKDT Thu Aug 2 2018

.ANALYSIS AND UPPER LEVELS...

An upper level low centered over Saint Matthew Island is visible
on water vapor imagery with the leading front pushing across the
center of the state this morning. At the surface, low level
stratus and foggy conditions persist over much of the Bering and
western coastal areas. Just south of this low, a strong upper
level jet, reinforced by a ridge in the North Pacific, has values
maxing out near 140 knots and is creating a wide swath of zonal
flow and pushing moisture on shore. In response, radar imagery
indicates rain is falling across much of southwest Alaska and the
AKPEN this morning, moving east towards Southcentral.

&&

.MODEL DISCUSSION...

Overall, model solutions are in good agreement with the large
synoptic scale pattern through the weekend. The main challenge in
the short-term will be timing of precipitation as a series of
shortwave troughs are generated across Southcentral in response to
the Saint Matthew Island low traversing the state and moving into
the Gulf by Fri morning. By Sat morning, models are hinting at a
Kamchatka low moving into the western Bering, however this remains
contingent upon the strength of the North Pacific ridge. Stay
tuned!

&&

.AVIATION...
PANC...A front moving up the Cook Inlet will bring rain and MVFR
ceilings to the airport this morning. As the low center moves into
the Gulf later this morning, increased cross barrier flow should
help to dry the low levels out some bringing ceilings up to low
VFR levels, though rain should persist through tonight. Winds
should remain fairly light for the period switching from
southwesterly to northerly as downsloping kicks in later this
morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper low currently centered over the northern Bering Sea will
drop rapidly southeast, reaching Kodiak Island early Friday
morning and then racing across the Gulf through Thursday
afternoon. Rain will cover most of Southcentral through tonight as
this low has good dynamics and moisture associated with it. Also,
winds will approach Gale force in the northern Gulf as a strong
surface low forms ahead of the upper low later today, which will
then fall behind the upper low later tonight and Friday. Upper
level high pressure will build over the area on Friday in the wake
of the low leading to drying and warming conditions. Low level
offshore flow will also be fairly strong on Friday due to the
surface low in the Gulf. The offshore flow will weaken Friday
night as the surface low moves south.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A more progressive weather pattern has set up across much of
Bering and southwest Mainland, with a fairly strong zonal jet
over the southern Bering and a ridge beginning to amplify over
the western and central Aleutians/Bering. This pattern features a
series of quick-moving troughs and fronts, with the first wave
continuing wet and cloudy conditions over the area as the wave
tracks through the southwest mainland this morning. Rainy and
cloudy conditions will persist through Friday morning as the upper
low over the northern Bering and its surface low counterpart
dives southeast across the southwest Mainland. Conditions improve
briefly for Friday as high pressure builds over the southwest
mainland. This will be short-lived, however, as a weak warm front
approaches the forecast area Friday night with increasing clouds
and a chance of rain for the start of the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The active pattern set up across much of the Bering and Aleutians
will remain in place through the weekend. The vertically stacked
low will begin to dive southeastward along the southwest coast and
enter the western gulf by Friday morning. By this afternoon, a
surface low will track west of the western Aleutians, with its
associated front bringing gale-force gusts and rain to the
western Aleutians and Bering through late Friday morning. The
north Pacific ridge begins to build northward and amplify slightly
over much of the southern Bering and Aleutians by Friday
afternoon. This feature will persist over the area into the
weekend, yielding stratus and fog to develop over parts of the
Aleutian chain and Bering sea. Gusty winds along the eastern
Aleutians and AKPen are expected to increase tonight under the
northwesterly flow pattern and persist through late Friday
morning.

&&

.LONG TERM FORECAST (Days 4 through 7)...
Beginning this weekend, a stagnant pattern will begin to setup as
a cutoff low from the Gulf moves southward into the North Pacific
and becomes nearly stationary. This will allow for a ridge of
high pressure to ride up along a broad trough that will setup over
the Northern Mainland, providing persistent zonal flow for most
of the Bering and South Mainland into early next week. This will
allow for a series of frontal systems from the Bering to move
through the South Mainland for later this weekend into the early
next week, allowing for a wet start to next week for most areas.

By the middle of next week there uncertainty begins to develop
with how deep a trough diving from Eastern Russia will move into
the Bering. This will erode away the ridging that will setup over
the Bering and allow for continued active and likely wet weather
for most of the area into the later portions of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales 132 178 352.

&&

SYNOPSIS AND MODEL DISCUSSION...KO/KVP
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...DEK