Small Craft Advisory 411, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKDT Mon May 21 2018

.ANALYSIS AND UPPER LEVELS...
The pattern remains much the same as the past few days. A broad
trough over the southern mainland and the Gulf of AK continues to
be the dominant weather maker. Several fronts continue to pinwheel
in this cyclonic flow. These are producing plenty of rain along
the Gulf coast with widespread cloud cover across just about all
of Southcentral AK. Showers are also making it over the Kenai and
Chugach mountains this morning and clipping stations around the
Cook Inlet. Showers dissipated over Southwest AK earlier last
evening. But with plenty of moisture and light flow, low stratus
and fog have set up shop over the YK-Delta.

The jet remains fairly amplified as we move towards late May. It
comes into the domain at 130+ kts supporting a developing surface
low near the Western Aleutians. It then quickly climbs over a
shortwave ridge in the Bering before diving back south to support
the afore mentioned trough over the Gulf at 130 kts.

&&

.MODEL DISCUSSION...
Models remain in rather good agreement in a somewhat stagnant
pattern. The result is moderate to high forecast confidence. There
might be some minor differences on the low the in Gulf and
specific timing of its associated fronts. However, this will have
little impact on sensible weather across the area. Instability
will work in tandem with the thermal trough across Southwest AK
today to produce some of the best convection of the year so far.
The higher resolution models (NAM Nest) and some hand edits were
used in handling these features.

&&

.AVIATION...
PANC...VFR conditions will persist. Another bout of southeast
winds should push into the terminal this afternoon and evening.
While timing could be off an hour or two, gusts should top out
near only 20 kts or so.

&&

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

Persistent upper level cyclonic flow continues as the dominate
upper level feature. At the surface a series of surface lows and
accompanying fronts will move north and west across the Gulf. The
majority of the rain will fall along the coasts as cross-barrier
flow will keep inland areas under sporadic showers and a little
sunshine at times. A combination a strengthening interior thermal
trough and coastal ridging will generate gusty southerly winds
across west and south Anchorage, out of the Knik River Valley, and
along portions of the Copper River during the afternoon and
evening hours through Tuesday. Otherwise, expect gusty easterly
winds along Turnagain Arm.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)... The
thermal trough stretched across Southwest Alaska today will bring
a good potential for isolated to widely scattered thunderstorms
this afternoon and evening. The best chance for thunderstorms
looks to be along and just to the west of the thermal trough axis
stretching from the middle Kuskokwim Valley south into the Greater
Bristol Bay area extending south to the coast just to the east of
Dillingham. With instability diminished on Tuesday precipitation
should remain showers and be more limited in coverage. The same
general pattern will continue on Wednesday, although with inland
shower coverage more isolated and a dissipating frontal system
approaching the coast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
An upper level ridge will track from west to east across the
Aleutians and Bering today and tonight. A frontal system following
on the upstream side of the ridge will reach the western
Aleutians this afternoon and the central Aleutians tonight. The
front will slow and shear apart as it continues east Tuesday and
Tuesday night before stalling over the eastern Bering and Alaska
Peninsula Wednesday and then dissipating Wednesday night. The
large vertically stacked parent low will follow, crossing the
western Aleutians Tuesday afternoon and then continuing slowly
east to the south central Bering through Wednesday night.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A progressive pattern will continue through next weekend, with an
upper low slowly tracking northward through the Gulf through
Thursday morning and another low tracking eastward across the
Bering/Aleutians through Friday. Models remain in fair agreement
with this cooler, cloudier, and unsettled pattern lingering over
much of the area into next weekend.

A triple point low will develop over the Gulf along the
approaching front by Thursday, and continue its progression
northward into Friday morning. This system will bring rain and
gusty winds to the surrounding Gulf areas as the front pushes
into the coast and further inland by friday night. The strong
southeasterly flow associated with these systems will favor
slightly drier conditions over the downsloped areas along the lee-
side of the Chugach range. Conditions will become more showery
overall and switch to an off-shore flow pattern by Saturday
morning, as the parent low tracks into the eastern Gulf through
next weekend.

Out West, the low over the western Bering will bring wet and
windy conditions to much of the Bering/Aleutians through Friday,
as it tracks eastward and crosses the AKPen into the northern
Pacific. High pressure will build into the western Bering and
Aleutians Friday, and continue to build eastward over much of
the area by Sunday morning.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 119 120 130.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JER
LONG TERM...TP