Small Craft Advisory 543, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
714 PM AKDT Thu Jul 12 2018

.ANALYSIS AND UPPER LEVELS...
The radar is quiet today following a soggy period over
Southcentral. A high deck of clouds is riding the northwest flow
over Kodiak Island, Southwest Alaska, and the southern end of the
Kenai Peninsula signaling a brief period under control of high
pressure. A sunshine warning is in place for Prince William Sound.

Aloft, northwest flow is in charge of Southcentral with the jet
entrance region moving into the Susitna Valley. An upper-level
trough covers the Bering in a sharp, closed pattern.

At the surface, low pressure is hot on the ridge's heels and is
currently west of the Pribilofs. It's stronger partner in the
North Pacific is just loping by the Aleutians. The combination is
creating gusty winds and rain over the AK Pen west to the central
Chain where only satellites sense the precipitation.

&&

.MODEL DISCUSSION...

Models began the day in lock-step and continue through Friday in
excellent agreement. A second low appears south of Adak by 00z
Saturday. While there's agreement in the strength of this low, the
NAMs position is jumping around while the GFS is consistently
slower.

In any case, this low is absorbed by the Bering Sea low by early
Saturday morning as it passes South of the AK Pen. Another low
moves into the western Chain Saturday morning with similar timing
issues into the weekend.

&&

.AVIATION...

VFR conditions will continue through Friday. Gusty southeast winds
will develop by Friday afternoon and persist into the evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The weak ridge over the southern mainland will be pushed east in
response to the incoming front associated with the Bering Sea low
beginning Friday afternoon. In advance of this front, the ridge
will sharpen along the North Gulf Coast resulting in an
isallobaric push typical through the Chugach Mountains Friday.
Thus we anticipate an increase in the Turnagain Arm wind and wind
across the Hillside, although not the strong winds we have
recently seen. This will also result in southerly wind pushing up
along the Copper River Friday afternoon. A frontal low forms in
the Barren island area late Friday that will result in the wind
turning down Cook Inlet Friday afternoon. The brief period of
sunny skies over the southern mainland will yield to another round
of clouds and areas of showers or rain. Along the coastal side of
the mountains expect rain to sweep in beginning Friday morning
across Kodiak Island than spread to the Kenai Peninsula and Prince
William Sound region through Friday evening. On the leeward side
the initial down slope will keep conditions drier, however, rain
or showers will be likely over the Cook Inlet region with more
of a scattered showers regime up into the Susitna Valley and into
the Copper River Basin. as we move into Saturday the low both
aloft and at the surface moves into the Prince William Sound
area, thus the down slope influence will end and we should see
more widespread showers across the southern mainland Saturday. The
upper low then moves off to the east Sunday, however, an upper
level trough swings through the Susitna Valley, Copper River
Basin, Kenai Peninsula and Prince William Sound Sunday. This will
keep the threat of rain and showers up through the weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
After pleasant weather across SW Alaska today, the region will
see a return to cooler and wetter conditions. Low pressure
spinning across the Bering Sea has an attendant weather front that
will move across the AKPEN tonight, and into the mainland into
the morning hours. Rain and wind will spread through the region
with the front and persist through Friday evening. As the Bering
Sea low slowly moves across the area, fairly unsettled showers
will linger until late Saturday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
An upper level low over the northwestern Bering Sea will phase
with a low that is moving out of the North Pacific late tonight.
This merged low will take until Saturday to move east of the
Bering. Cold air advection behind the departing system isn't
overly strong, and weak convective showers aren't looking too
likely. On the heels of this system is another developing low that
is currently spinning south of the Kamchatka Peninsula. This will
bring another chance of rain across the Aleutian chain through
late Friday.

&&

.LONG TERM FORECAST (Days 3 through 7)...

A progressive pattern is on tap for this forecast period. The
long term forecast period begins Sunday evening and commences with
a longwave trough spanning from the Yukon Territory to the Gulf
Of Alaska and ridging over the Central Aleutians. By Tuesday both
the GFS and the ECMWF depict a second trough pushing out of
Russian and into the Western Bering and Western Aleutians. This
new low will bring the ridge over Southcentral AK and Prince
William Sound Wednesday and Thursday. If this solution pans out,
anticipate widespread subsidence and expect a warming trend for
the Anchorage Metro Area and the Mat-Su valleys.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 173.

&&

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...SA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SS
LONG TERM...PS