Small Craft Advisory 360, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKDT Wed May 8 2019

.ANALYSIS AND UPPER LEVELS...
The primary feature in play this afternoon is a large upper level
trough that extends from the Bering Strait to south of Adak.
Rounding this upper level trough is a potent 160 kt jet that
weakens as it exits near the Copper River Valley. This is driving
a complex low through Prince William Sound this afternoon.
Accompanying this low is a front that is bringing extensive rains
to the coast and areas inland. Behind this front, rain showers are
becoming few and far between while pronounced breaks in the
clouds will work through Southcentral this evening.

&&

.MODEL DISCUSSION...
Through the short term, models are all in good agreement handling
both the synoptic and mesoscale features with little difference.
Minor differences start to creep into guidance by Friday as they
struggle with where a potent shortwave will lift through. Those
translations down to the surface equate to a low hanging out
around Kodiak, keeping a tight pressure gradient across PWS.

&&

.AVIATION...
PANC...Showers will continue to wane through the afternoon hours
while winds increase out of the SSE. CIGS and VISBY will improve
to VFR with occasional holes of sunshine and remain that way
through tomorrow. Cross barrier flow will keep the terminal mainly
dry tomorrow afternoon though wind shear is also likely to
develop Thursday afternoon.

&&

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

Low pressure across the Copper River Basin continues on a
northward track this evening with the front diminishing and rain
tapering off to scattered showers mainly along the mountains. The
next storm pushes a front across the Gulf late tonight spreading
rain and gusty easterly winds to Kodiak. The leading boundary
pushes north ahead of the developing low making it across the
eastern Kenai and Prince William Sound on Thursday.

Thursday night through Friday the low pressure system driving the
front over the Gulf becomes an organized stacked system as a new
upper low closes off around the base of the trough near Kodiak
Island. Winds across the Gulf, Kenai and Prince William Sound
will be the first to experience the strength of this rapidly
evolving storm with max gales and storm force winds across marine
waters. By the time the low tracks inland across Bristol Bay late
Friday morning, gusty winds pick up across much of Southcentral.
Winds across the region are expected to peak Friday afternoon
before tapering down Friday evening. The front will bring the
highest rain accumulations across the eastern Kenai and Western
Prince William Sound as downsloping across the mountains limits
rain amounts inland.

Saturday the weather will be relatively quiet as the strong
surface low fills on its westward track to the Bering and the
frontal boundary washes out as it pulls north across the interior.
Scattered showers remain in the forecast as upper level waves
rotate across the region from the main low over the Bering.

&&

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

A moist southwesterly flow, combined with a vertically stacked low
off the west coast and a weak shortwave lifting northeast across
the Southwest interior, will keep scattered showers over the
region through the first half Thursday. By late Thursday, a
frontal system associated with a deepening surface low tracking
northward near Kodiak Island will move across Southwest Alaska
from east to west. This system will bring another round of
widespread cloud cover and rainfall to the region through the
first half of Friday. The widespread rainfall will transition to
scattered showers late Friday into Saturday as the low weakens
and tracks northwest over the Y-K Delta.

&&

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

A series of shortwaves will continue to pinwheel around a broad,
cyclonic upper-level trough bringing areas of rain and small-
craft winds to the western Bering and along the Aleutian Chain
through the start of the weekend. The first of these more
organized features is currently situated over the central
Aleutians and will weaken overnight as it slides south. A second
shortwave will move from the western Bering over the central
Aleutians for Thursday afternoon before continuing to track east
for Friday. A third shortwave follows a similar track, bringing
yet more rain and gusty winds to the western Bering for Friday
and the Aleutians late Friday into Saturday.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...

Lingering southwesterly gale force winds in Shelikof Strait and
along the southwestern Gulf coast will subside to small craft by
Saturday morning as the Gulf low lifts northward over southwest
Alaska. By Saturday afternoon, model solutions indicate another
North Pacific low moving into the Gulf, though there is little
agreement on the exact track. This low may introduce the
possibility of another round of gale force winds over the same
area (Shelikof Strait and the southwestern Gulf) Sat night into
Sun morning, however confidence remains low due to uncertainty.
Across the Bering, there is high confidence there will be no
high winds or waves through Monday.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

Two main features for the long term include a broad upper level
trough over the eastern Bering and a high amplitude ridge over
the Yukon. Although models quickly become inconsistent by Monday,
the general trend shows several upper level waves rotating around
the upper level trough. This will likely perpetuate unsettled
weather conditions over the southern half of the state through
early next week. A possible reprieve from the unsettled weather
may arrive midweek if the ridge over the Yukon maintains its
strength.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 119 120 130 131 132 138 139 150 155.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SS
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...KO