Small Craft Advisory 457, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
411 AM AKDT Sun Jun 10 2018

.ANALYSIS AND UPPER LEVELS...
A familiar pattern is in place across the southern mainland this
morning as weak upper level flow continues to support generally
pleasant conditions characterized by isolated diurnal convection
from Southcentral to Southwest Alaska. Elsewhere, high pressure
continues to support extensive marine stratus and some patchy fog
across much of the Bering Sea and Gulf of Alaska, with these
conditions once again encroaching upon coastal areas from the
Kuskokwim Delta to Cook Inlet and eastern Prince William Sound.
Well to the north, an impending pattern change is beginning to
take shape as a deep Arctic trough digs aggressively over the
North Slope. The first evidence of this for Southcentral AK can be
seen on satellite imagery this morning in the form of increased
mid and high level cloud cover beginning to stream across the
Alaska Range from the north.

&&

.MODEL DISCUSSION...
Models remain in good short term agreement as the Arctic trough
continues to dig southward towards the Gulf coast through Monday.
Some notable differences begin to emerge by Monday night, with the
NAM becoming somewhat of an outlier in keeping the trough axis
farther east over Prince William Sound and not digging as far
south into the Gulf. For this reason, started to trend the
forecast more towards GFS early in the work week after utilizing
NAM for the remainder of the weekend.

&&

.AVIATION...
PANC...Light winds will give way to a moderate sea breeze at the
terminal by early afternoon in response to daytime heating and a
relatively weak pressure gradient over the Cook Inlet region. An
approaching trough will bring the possibility of rain showers to
the terminal tonight, with ceilings lowering to around 5000 ft but
expected to remain VFR at this time.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A weak upper trough moves south across Southcentral today bringing
isolated to scattered showers. There is a slight chance for
thunderstorms over the southern Copper River Basin this afternoon
and early evening. A strong upper trough digs south across
Southcentral later tonight and Monday and brings cooler
temperatures and widespread showers and rain to many areas north
of the Kenai Peninsula. Models differ some on the western extent
of the rain/showers, but looks to be close enough to warrant
increasing pops across the Anchorage Bowl and Matanuska Valley
for Monday.

&&

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

A trough will drop southward across the region over the next few
days. The lead edge of vorticity aloft will cross the region
today, as northerly flow develops. the main push of the trough
looks to affect the region on Monday, with the brunt of the
coldest air aloft skirting the Alaska Range as the core makes in-
roads for the Cook Inlet. Still, this will bring a reinforcing
shot of northerly flow. What this means for southwest Alaska is
look for continued northerly flow to reinforce the amount of dry
air, with Sunday being the warmest day, as 850 mb temperatures
cool 4 to 6 deg. C on Monday as the second and stronger impulse
pushing into the area.

The dry air advection (horizontal movement of an airmass) will
also help increase afternoon winds as the colder dense air tries
to mix down to the surface. This could allow for somewhat breezy
conditions to develop. Conditions look to warm a few degrees for
Tuesday, but, another disturbance in the flow could allow for
breezy conditions to continue for locations north and east of
Lime Village.

&&

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

The low which has affected portions of the central Aleutians
yesterday and this morning will continue to move southeast of the
region through the day, with precipitation, winds, and waves
diminishing by tonight. Another low bypassing the western end of
the chain looks to bring a  period of small craft condition winds
to that region today through Monday afternoon.

Otherwise, the main story will be high pressure building across
the region which should at least allow for some breaks in the
stratus to develop over portions of the Bering sea, with the
eastern Bering into the Pribilof Islands standing the best chance
of seeing this, as offshore flow brings drier air into this part
of the area for Monday and Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
By Tuesday, a trough extending from an upper low over the Arctic
Ocean will stretch south to cover the eastern half of mainland
Alaska, including Southcentral. This initial trough will rotate
off to the east into the Yukon Territory while the main low drops
south over northern Alaska through Wednesday. The upper low will
then dig south southwest into western Alaska Thursday and Friday
with the upper ridging over the Bering weakening in response.
Meanwhile, a low containing the remnants tropical system Maliksi
will track into the area south of the Alaska Peninsula Thursday or
Friday. The GFS brings this low north the fastest, phasing and
merging it with the arctic low/trough in western Alaska on Friday
while the ECMWF and Canadian models keep it further to the south
as a separate feature which moves into the southwestern Gulf
Friday or Saturday. While there are some notable timing and track
differences between the three models, all are in agreement with
the idea of a pattern shift to wetter southerly flow for Friday
through Sunday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None
MARINE...None

&&

SYNOPSIS AND MODEL DISCUSSION...CB
AVIATION...CB
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...JR

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1137 AM AKDT Sun Jun 10 2018

AKZ145-121945-
Susitna Valley-
Including the cities of Talkeetna, Willow, and Cantwell
1137 AM AKDT Sun Jun 10 2018

...THE YETNA RIVER AT LAKE CREEK IS AT BANKFULL...

The water level on the Yetna River at Lake Creek is bankfull at
this site due to ongoing snowmelt in the mountains and local
rainfall. We anticipate these conditions may persist for several
days as additional rainfall is forecasted in the area. There are
no expected impacts at this time for this event.

SPECIAL WEATHER STATEMENT...CORRECTED
National Weather Service ANCHORAGE AK
1146 AM AKDT Sun Jun 10 2018

AKZ145-121945-
Susitna Valley-
Including the cities of Talkeetna, Willow, and Cantwell
1146 AM AKDT Sun Jun 10 2018

...THE YENTNA RIVER AT LAKE CREEK IS AT BANKFULL...

The water level on the Yentna River at Lake Creek is bankfull at
this site due to ongoing snowmelt in the mountains and local
rainfall. We anticipate these conditions may persist for several
days as additional rainfall is forecasted in the area. There are
no expected impacts at this time for this event.

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1150 AM AKDT Sun Jun 10 2018

AKZ111-122000-
Matanuska Valley-
Including the cities of Palmer, Wasilla, Sutton, and Chickaloon
1150 AM AKDT Sun Jun 10 2018

...THE MATANUSKA RIVER AT PALMER IS AT BANKFULL...

The water level on the Matanuska River at Palmer is bankfull at
this site due to ongoing snowmelt in the mountains and local
rainfall. We anticipate these conditions may persist for a couple
of days as additional rainfall is forecasted in the area.

EXPECTED IMPACTS:

Localized minor out-of-bank flooding may occur, especially along
parts of the Glenn Highway east of Sutton from milepost 64 to 66.
Boaters should anticipate potential debris associated with high
water.