Small Craft Advisory 467, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
519 AM AKDT Thu Jun 14 2018

.ANALYSIS AND UPPER LEVELS...

Scattered showers occurred once again yesterday across portions
of the Copper River Basin, Susitna Valley, and the Lower Kuskokwim
Valley, with a couple isolated thunderstorms east of Koliganek in
the Bristol Bay area. Elsewhere, plentiful sunshine dominated over
the Kuskokwim Delta and southern Bristol Bay. Across the Bering,
the usual fog and stratus persisted across the southern half of
the sea, while the northern half got to enjoy an unusual mainly
sunny day. Temperatures remained in the 60s across most of
Southcentral, with 70 reported in Seward and Kodiak. Lower 70s
were much more common across the Lower Kuskokwim Valley and
Bristol Bay with the highest temperature in southern Alaska
reaching 76 in Koliganek.

In the upper levels, most of the area is in a primarily stagnant
pattern of light northwest flow aloft. A deep low over the North
Pacific south of the Aleutians will be making its way northward
into the Bering by Saturday, helping induce a pattern change
towards the wetter side. A bit more cloud cover than expected
developed from Kenai northward overnight as a weak upper level
wave helped enhance the lift over the area.

&&

.MODEL DISCUSSION...

The models are in good agreement on the handling of the major
synoptic features affecting Southern Alaska over the next couple
days. A strong low over the north Pacific will track northward
into the Aleutians by Saturday, bringing the first of several
rounds of precipitation to the area. Other than some minor
differences in the placement of the low, the main differences
between the models mainly regard timing and the location of the
smaller scale features. All of the models have slowed down the
onset of precipitation by about 6 hours. A GFS/SREF blend was used
for precipitation field updates in the current forecast package.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist through this
morning. The Turnagain Arm wind will increase during the afternoon
today. This will lead to gusty southeast winds over the airport
which will persist into the overnight hours tonight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Westerly flow aloft today and tonight will keep much of the area
fairly dry. The flow today will be slightly cyclonic, which is
allowing some clouds to remain over the area. Some isolated
showers are also possible, mainly from about Anchorage northward.
Some ridging will build into the southern mainland tonight, ahead
of an approaching weather system from the south. This is the
beginning of a pattern change. The leading front will reach Kodiak
Island tonight, then surge northward to the Kenai peninsula Friday
morning. Rain will spread over most of Southcentral on Friday.
Gusty winds are expected out of Turnagain Arm and along the Knik
and Copper Rivers. With deep/moist southwesterly flow however,
these winds are not expected to produce much downslope drying for
inland areas.

&&

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

The longwave pattern features high pressure over the Bering and an
upper low over the North Slope with the trough axis descending
into the Alaska Range. Expect dry conditions all of today and
tonight. The much advertised low over the North Pacific is very
prominent on satellite imagery. The leading edge of the cloud
shield is just starting to move into the Central Aleutians. Today,
this mature low in the North Pacific will move north across the
Aleutians and AKPEN bringing increased cloud coverage and rain to
the region beginning Friday. The low is tracking a little slower
than orginally anticipated pushing the timing of the precipitation
back. Saturday and Sunday are looking wet and gloomy.

&&

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

A dome of high pressure continues to dominate the Bering. The
latest ASCAT/advanced scatterometer pass has the surface high west
of St Matthew Island. Today an organized low will continue its advance
towards the Aleutians. This will shift the position of the high in
the Bering. It will also bring gale force winds into the region.
The surface low will cross the chain near Unalaska Saturday
afternoon.

&&

.LONG TERM FORECAST (Days 3 through 7...Sat through Wed)...
The long term pattern continues to look like a major shift away
from the mostly sunny and mild start that we have seen for June.
The general idea of the broad longwave trough establishing itself
over the Eastern Bering holds true and all models remain in near
"lock-step" with the synoptic set-up. Now, there is starting to be
some more clarity with individual waves of energy and when the
heaviest bouts of rain will be.

Sat will start for most of the region with the initial front
departing to our north. With potent southerly flow continuing to
pump moisture into the mainland, all areas will remain highly
vulnerable to showers. The best chance for these will be along
southerly facing terrain and the north Gulf Coast. The next best
defined shortwave will move quickly from south to north across the
Gulf of AK late Sun night into Mon morning. This will bring
another round of moderate rain from the Gulf Coast into the Cook
Inlet. This batch of rain will eventually move into SW AK and the
Susitna and Copper River Valleys later Mon. It will also stir up
another round of gusty southeasterly winds. West of the trough
axis over the Western Bering, flow will remain out of the north.
This will keep things quite dry across that area, but we can never
rule out widespread low clouds developing as June is a
climatological peak for marine stratus.

Beyond Mon, uncertainty starts to creep back in regarding
individual waves of energy. But the overall cloudy and showery
pattern will hold over most of southern AK through the week. There
are some signs of hope by the end of the week as the parent low
ejects northward and ridging tries to nudge in from the N Pacific.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...GALE 131 172 174.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
LONG TERM...JR