Small Craft Advisory 390, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 AM AKDT Fri May 8 2020

.ANALYSIS AND UPPER LEVELS...

A large area of low pressure centered hundreds of miles south of
Kodiak Island is spreading clouds and moisture all across Southern
Alaska this morning. The low itself will get a bit closer, but the
center remains well south of the area. The key features of impact
are an occluded front causing strong winds through the mountains
and the gaps, strong easterly onshore flow into Kodiak Island with
around an inch of new rain reported over the last day or so, and
scattered shower activity across Southwest Alaska. Temperatures
crashed nearly 20 degrees from two days ago yesterday, with many
areas struggling to hit the 50 degree mark. Across the Kuskokwim
Delta where the clouds were last to come in, highs soared well
into the 60s yesterday. Satellite shows much of the cloud cover
across all of Southern Alaska is a stratiform type, so despite
very unstable conditions in the lower atmosphere, it is not
translating to any convective shower activity, as the cloud layers
are above much of the instability, which is also a dry air mass.

In the upper levels, a strong upper level low is vertically
stacked with the large surface low well south of Kodiak. This is
keeping the upper levels very amplified, with the associated
trough extending down to 35N latitude. Meanwhile, ridging is
building into the western Bering, and a second area is also over
the Rockies.

&&

.MODEL DISCUSSION...

The models continue to be in excellent agreement regarding the
evolution of the large scale weather pattern. Precipitation at the
coast, particularly in Kodiak and along the Kenai Peninsula, and
the strength and timing of the gap winds remain the primary
forecast challenges. The strength and timing of the winds through
the Knik River Valley have been particularly challenging thusfar.
Overall forecast confidence remains very high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist into this
afternoon. After 00Z, the Turnagain Arm wind will approach the
area, which could cause gusts to 20 kt at times into the evening.
The winds will diminish late tonight.

&&

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

An occluded front over the northern Gulf slowly weakens through
this evening. With strong southeasterly flow in the lower
elevations, the brunt of the rain will fall along the coasts with
general downslope drying mitigating any significant rainfall
inland of the coastal mountains. Gusty gap winds are expected
across Turnagain Arm and out of the Knik River Valley. With a
strengthening thermal trough inland and ridging along the coast,
the Turnagain Arm wind will bend into town this afternoon along
with winds becoming fairly gusty there and out of Knik River
Valley. Winds in most areas will diminish tonight.

Drier and warmer conditions are expected with decreasing cloud
and warming 850 mb temps associated with an intensifying thermal
trough inland. Afternoon highs on Saturday will be in the 60s in
many inland areas with RH values in the 20s. The good news is
there will not be much wind other than relatively light local wind
regimes inland and perhaps coastal sea breezes Saturday.

&&

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

Gusty winds that were in place across the Alaska Peninsula have
diminished this morning. A few scattered showers near the Bristol
Bay area are expected to dissipate through the afternoon hours.
Conditions across Southwest will remain fairly quiet until an
upper level wave arrives by Sunday. This disturbance will likely
produce a short period of gusty winds, especially across the
Bristol Bay area and coastal regions. With elevated midlevel
southeasterly winds still in place, most areas should remain dry
due to downsloping.

&&

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

The leading front associated with a storm force low has reached
the western Aleutians this morning. Rain and gusty winds will
spread across the Chain through the day. As the front moves
eastward, winds are expected to increase to storm force over the
western Bering as the low strengthens and passes just west of
Shemya. By this evening, the front occludes and stalls near the
Pribilof Islands. On the backside of this low, colder air
wrapping in will allow for a showery regime across the western
Bering for the weekend. The remnant frontal boundary remains
nearly stationary over the eastern Bering through Sunday.

&&

.MARINE (Days 3-5 Sunday through Tuesday)...
The general pattern will consist of low pressure over the Bering
Sea and Aleutians, and high pressure over mainland Alaska and the
Gulf. Winds are expected to stay below gale force, with small
craft advisory winds limited to the Aleutians and Bering.

&&

.LONG TERM FORECAST (Days 4-7 Monday through Thursday)...
The general pattern for the extended portion of the forecast will
consist of a ridge over mainland Alaska and a trough over the
Bering Sea and Aleutians. The pattern will have a negative tilt,
with the interface between the ridge and trough roughly over
southwest Alaska. The main forecast challenge is the degree to
which clouds and precipitation will be over southwest Alaska (and
possibly Southcentral by Thursday) at that interface between the
trough and ridge. Temperatures will mostly be above normal.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning: 155.
		 Flood Advisory: 155.
MARINE...Storm Warning: 411-413.
Gale Warning: 119 120 130 131 138 139 173 175 177-179 185 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...BL