Small Craft Advisory 481, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
545 AM AKDT Mon Jun 15 2020

.ANALYSIS AND UPPER LEVELS...

An upper level low centered near Unalaska is leading to scattered
showers across the eastern Bering/Aleutians. More benign
conditions farther west are observed under building high pressure.
Embedded shortwaves in the aforementioned upper low are moving
northeastward across Bristol Bay and the Kuskokwim Delta. These
brought scattered thunderstorms over this region during the
daytime hours yesterday, though they have since died off as
stability has increased overnight. Showers are still relatively
widespread over the Kuskokwim Delta and Alaska Peninsula as latest
water vapor imagery shows ample moisture remaining present over
these areas. Weak upper troughing is bringing a few clouds across
Southcentral, but otherwise conditions are calm given the drier
conditions aloft as well as weak overall flow. A more potent
easterly wave is leading to light showers moving westward over
portions of the Copper River Basin this morning.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement. As usual, embedded
shortwave troughs will make exact timing/placement of
thunderstorms difficult through Tuesday near the Alaska Range. As
a low approaches Kodiak Island by Tuesday afternoon, local wind
effects will need to be more closely examined. While a Turnagain
wind appears likely, the strength of the thermal through over the
interior will determine if it will bend into the Anchorage bowl.
More cloud cover would obviously weaken the trough and cause winds
to be more confined to the coast. Models remain somewhat in
disagreement regarding this with GFS/ECMWF much more overcast than
NAM/Canadian. Confidence is average.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

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

The last of a long series of easterly waves can be seen over the
eastern Copper River Basin this morning. This should provide the
last round light convection over the Copper River Basin,
Talkeetna Mountains, and eastern Chugach later today before
pushing northwest tonight. As the wave moves out, some showery
activity may persist over the high terrain through Tuesday.

The next weather feature for the coming week will be the upper
level shortwave arriving just to the south of the Akpen Tuesday
morning. Its surface low is forecast to remain near the Akpen,
but the eastward extending front is expected to bring persistent
rain to Kodiak Island starting early Tuesday morning. Frontal
precipitation should push north all the way through to the Prince
William Sound by Tuesday night. Areas on the eastern side of the
Kenai Peninsula and the Anchorage Bowl should stay mostly dry due
to downsloping. Mass convergence along the Southcentral coastline
as the front moves northward will create a coastal ridge,
bringing Gale force winds through Shelikof Strait and the Barren
Islands beginning Tuesday night. The strong pressure gradient and
remnants of a thermal trough in the Susitna Valley will also
create gusty winds over the Turnagain arm and into Anchorage
Tuesday afternoon and well into the night.

&&

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

The broad cyclonic circulation over the eastern Bering continues
to be the driver for sensible weather in Southwest Alaska. A
series of shortwave disturbances have brought some rain to the
Kuskokwim Delta coastal area this morning, as well as some
stratus and fog to the Pribilofs. This feature is being supported
by the main branch of the jet stream to the south. Monday looks to
be a quiet weather day for Southwest Alaska, but that all changes
Monday night. The upper low in residence will deepen as a surface
low in the north Pacific phases with the existing feature over
the eastern Aleutians. This will bring widespread rain showers and
gusty winds to Bristol Bay Tuesday night and Wednesday. The
Kuskokwim Delta and the Kuskokwim Valley will see widespread
showers on Tuesday and Wednesday. A passing shortwave trough on
Tuesday afternoon will present an opportunity for scattered
convection in the lower Kuskokwim Valley and portions of the
Kuskokwim Delta.

&&

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

The western Bering will remain quiet through the period, aside
from some fog and clouds. The eastern Bering will be dominated by
the upper low that presently resides east of Dutch Harbor. It is
pushing a series of shortwaves over Bristol Bay and back to the
Pribilofs this morning. Monday will see some scattered rain
showers in the eastern Chain and western AKPEN as persistent
southerly flow pushes more moisture across the AKPEN. Things get
going on Monday night as the surface low in the North Pacific
phases with the upper low and widespread rain and gusty winds
develop from Cold Bay eastward through Tuesday. Model guidance
suggests that the low will remain semi-stationary on Wednesday
over the AKPEN and elongate east to west with some widespread rain
shower activity back to the Pribilofs and south to Dutch Harbor.

&&

.MARINE (Days 3 through 5... Wednesday through Friday)...

Easterly gale force winds are expected along the northern Gulf
coast on Wednesday as a low center moves over the Alaska
Peninsula. Another system may bring easterly gale force winds to
the northern Gulf coast again on Friday afternoon, though there is
low confidence in the track at this time.

Over the Bering, the low moving over the Alaska Peninsula
Wednesday will bring northerly small craft winds over the central
and eastern Bering waters. This low retrogrades Wednesday night,
bringing northwesterly flow to the western Bering. Some gale force
winds are possible across the western Aleutians. Generally quiet
conditions are expected for the end of the week.

&&

.LONG TERM FORECAST (Days 4 through 7...Thursday through
Sunday)...

Some key features that have been consistent over the last few days
include a broad upper level low in place over the eastern Bering
and a ridge in place over the Yukon. Model solutions show fair
agreement with the low taking a southeasterly track into the
central Gulf by Saturday. Overall, this shift in the pattern will
bring cloudier skies and cooler temperatures for the southern
Mainland. Onshore flow along the northern Gulf coast will likely
bring rainy conditions for next weekend.

&&

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

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...LB
MARINE/LONG TERM...DK