Small Craft Advisory 363, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 PM AKDT Thu May 9 2019

.ANALYSIS AND UPPER LEVELS...

A developing storm system south of Kodiak has pushed a frontal
boundary across the Gulf which now stretches across the western
Gulf to the Kenai to Prince William Sound. The diffuse boundary is
spreading clouds inland with only light rain along higher elevations.
Low pressure across the Bering is initiating a few showers along
the Southwest coast, otherwise weather is relatively benign.

&&

.MODEL DISCUSSION...
Models continue to stay in good agreement with timing and strength
on the storm system expected to move up to the Gulf tonight
crossing to the Southwest on Friday. Only minor edits were made
using the higher resolution models to increase winds across
Southcentral.

&&

.AVIATION...
PANC...A low moving a front across the Gulf today will bring wind
challenges through Friday. Light northeasterly surface flow
continues through early Friday morning. A low level southeasterly
jet develops late tonight along the Turnagain arm...therefore,
wind shear is expected until the surface low moves near Kodiak and
the surface winds

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A low pressure system that is currently well south of the AKPEN
will continue to move towards Kodiak and deepen. This will result
in an increase of pressure gradient forces from Prince William
Sound to Cook Inlet. Therefore, we are expecting some terrain
enhancement and channeling for portions of Southcentral. High
confidence that there will be a wind event tomorrow afternoon and
into the night. The spotlight will be on Turnagain Arm and
Hillside area of Anchorage. However, portions of the Knik Valley,
Copper River and the Mat-Su area will also have gusty winds. The
second impact from this low will be moderate to heavy rains over
Prince William Sound. Most of the rain will fall along and near
the coast, with cross-barrier flow limiting amounts inland but it
is possible that light showers could make it into the Anchorage
Metro Area. The winds will diminish on Saturday as the parent low
weakens and decays.

&&

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

A front associated with a deepening low tracking toward Kodiak
Island will continue to spread clouds and widespread rain across
Southwest Alaska through the overnight hours as it lifts to the
north and west from Bristol Bay. On Friday, the low tracks
northwest from southern Cook Inlet to the interior Southwest as it
becomes vertically stacked. Clouds and showers will remain across
the region through Saturday as both the surface low and the upper
level low drift toward the Y-K Delta and a moist, southwesterly
flow develops. A few embedded thunderstorms are also possible late
Friday afternoon and evening from Aniak to Sleetmute as the
combination of daytime heating, vorticity advection, and cold air
advection in the mid-levels all act to increase lapse rates and
shear, helping to deepen convection in this region. Showers will
diminish on Saturday as a ridge builds in advance of the next low
moving toward the region from the north Pacific. A warm front
associated with this feature will bring rain to the AK-Pen by
Saturday night. Rain continues for the AK-Pen and Bristol Bay
through Sunday as the low tracks into the far eastern Bering.

&&

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

The broad upper-level low will will persist across the Bering
through the first half of the weekend. Smaller shortwaves embedded
within the larger synoptic feature will bring periods of showers
and gusty winds to the southern Bering and Aleutian Chain as each
pinwheels around the main area of cyclonic circulation. The first
of these currently sits over the central Aleutians and will track
east to eastern Aleutians through Saturday. A second trough
associated with the low crossing Southwest Alaska Friday and
Friday night will form into a small surface low near Nunivak
Island on Saturday and rotate southwest towards the Pribilof
Islands through Saturday night. Lastly, a north Pacific low will
approach the eastern Alaska Peninsula from the south Saturday
night. The shortwave associated with this feature will absorb the
the former, allowing the broader trough axis to shift slightly
east. This will also allow a ridge to build over the western
Aleutians and Bering by the end of the weekend, keeping most of
the active weather confined to the eastern half of the Bering.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

A North Pacific low lifts northward over the Alaska Peninsula and
into the eastern Bering on Sunday. Small craft winds are expected
in the southwestern Gulf of Alaska beginning Sat evening. Winds
will diminish by Sun afternoon. There is high confidence a broad
area of weak low pressure will remain over the Bering through Tue
with no significant winds or waves expected. Meanwhile, a second,
weaker North Pacific low approaches the Gulf Mon evening. At this
time, no significant winds or waves are expected for the Gulf of
Alaska Sun through Tue.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through
Thursday)...

The long term trend includes a broad upper level trough over the
eastern Bering with a ridge over the Alaska-Yukon border. By
Tuesday, the area of high pressure shifts over the northern half
of the state, allowing the trough to extend all the way over the
central Gulf. Models struggle to resolve how these two features
will interact, however there is a growing consensus that a series
of upper level shortwaves will rotate around the trough and lift
over the southern Mainland through Thursday.

&&

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

&&

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