Small Craft Advisory 626, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
401 AM AKDT Mon Aug 13 2018

.ANALYSIS AND UPPER LEVELS...
The jet core spans from Kodiak to the Yukon Territory. On
satellite imagery there is a wave along the frontal boundary near
Prince William Sound and a mid to upper level low over Southwest
Alaska. At the surface, the low is north of Bethel
with a value of 988 mb. The pressure gradient remains enhanced
over much of Southwest Alaska and portions of South Central. The
latest ASCAT/advanced scatterometer pass has detected gale force
winds in Bristol Bay and in the Eastern Bering. The radars at
Bethel, King Salmon and Middleton Island continue to be active
this morning.

&&

.MODEL DISCUSSION...
Models are decent agreement with the synoptic pattern. Expecting
the low over Southwest Alaska begin to fill, become an open wave
and get absorbed into the longwave pattern. Anticipate a
gradual decrease in the pressure gradient forces over the state.
The GFS and the ECMWF are in lock step with the new closed low
trekking across the Bering and towards Bristol Bay. Sensible
weather-wise, there are some differences with the timing of
precipitation of Southcentral, but they all depict rain for
Anchorage today.

&&

.AVIATION...
PANC...More gusty winds expected today at PANC. The latest
satellite image does show low and mid clouds over portions of the
Cook Inlet. Generally expecting VFR cigs with potential for the
ceilings to drop to 3500 to 4500 ft. Rain expected this TAF
period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The strong front which crossed Southcentral and the western Gulf
yesterday will exit to the eastern Gulf today. After a break in
rain behind this front, rain will once again begin to fill in from
west to east as short-waves eject out of the upper trough sitting
just to the west over the eastern Bering Sea and Southwest Alaska.
On Tuesday, the upper low will open into a trough and head strait
for Southcentral. With deep south to southwest flow, the heaviest
and steadiest rain through to Tuesday will fall in the Mat-Su,
along the south side of the Alaska Range including the Denali
Highway, and across eastern Prince William Sound. Anchorage will
also see rain, with the heaviest rain likely along the Chugach
Mountains. With rivers and streams in the Susitna River basin
still rising from yesterday's rain, expect many of these to rise
to near bankfull. There is potential for some minor flooding
depending on rainfall totals and distribution over the next two
days. Also, strong winds will persist across the western Gulf
and Cook Inlet, with gusty winds pushing onshore along the
Kenai Peninsula and on up to Anchorage.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

A 990 mb low northeast of Bethel this morning will continue to
fill in as it slowly drifts east. Two shortwaves, one currently
moving through Bristol Bay and a second moving into the lower YK-
Delta later this morning, will act to enhance the bands of
showers pinwheeling around the main low. High surf and coastal
erosion will remain a threat along the shores of Kuskokwim and
Bristol Bays through Monday evening as gusty west to northwest
winds continue to wrap around the back side of the low. A second
trough diving south through the eastern Bering will bring another
round of precipitation to the southwest mainland Monday night.
However, a fast-moving ridge undercutting and pushing ahead of the
trough will keep the shower activity from pushing all the way to
the Alaska Peninsula. A developing low in the eastern Bering will
kick the ridge east on Tuesday and bring another round of showers
to the AKPEN through Tuesday night. Lingering low-level moisture
along a cyclonic, northerly flow behind the western Gulf low will
keep scattered showers over the Aleutian and Alaska Ranges, as
well as over higher elevations across the southwest mainland,
through Wednesday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

Gusty west to northwest winds along with bands of showers will
continue across the eastern Bering through Monday. A developing
upper-level low will quickly drop south from eastern Russia,
reaching the Pribilofs early Tuesday morning. Its associated
surface trough will spread another round of wet and windy
conditions under northerly flow to the eastern half of the Bering
through Tuesday night. Across the Aleutians, a weaker surface
feature will undercut the southward advancing trough, bringing
rain to the central Aleutians late Monday night through Tuesday
morning. As these two systems move closer, they will phase and
develop a new surface low north of the eastern Aleutians. This new
system will quickly slide into the western Gulf by Wednesday
morning. Farther west, high pressure will develop over the western
Bering and Aleutians beginning Monday and remain in place through
Wednesday night. Widespread areas low stratus of fog are possible
through Wednesday under this ridge.

&&

.LONG TERM FORECAST (Thursday through Sunday)...
The models continue to struggle with the remnants of the cold
upper level low that will track from the Bering into the Gulf on
Wednesday. Uncertainty in this feature will continue to impact
primarily the rainfall forecast into Thursday, but with a
generally further south track than initially expected to odds of
a wet day with the potential for significant convection on
Thursday is diminishing.

Most of the area will see a break in the active weather late this
week of an incoming arctic trough that will descend the the South
Mainland this weekend. There is a large spread in the guidance in
how far southward this trough will move due to a rapidly
developing North Pacific low that will interact with the remnants
of Hurricane Hector that looks to approach the Gulf on Saturday.
While there still remains significant uncertainty for most of the
South Mainland, especially with regards to temperatures from the
arctic trough, there is very good model agreement that active
weather will return to the South Mainland for the upcoming
weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 352 351 130 138 139 140 414 160 165 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...DEK