Small Craft Advisory 342, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
436 AM AKDT Fri Apr 17 2020

.ANALYSIS AND UPPER LEVELS...

The overall synoptic pattern remains quite similar to previous
days. A broad ~985mb low currently located southwest of Adak is
leading to widespread showers over the western Bering/Aleutians.
Strong upper level southerly flow ahead of it is continuing to
bring steady rain to the central and eastern Aleutians, extending
northward through the Kuskokwim Delta. Gusty winds are likewise
observed on the Pacific side of the eastern Aleutians and Alaska
Peninsula. Farther east, an upper level ridge remains in place
over Southcentral and the Copper River Basin. As such, dense fog
is expected this morning across the western Kenai Peninsula as
well as along Turnagain and Knik Arm.

&&

.MODEL DISCUSSION...

Models generally remain in good agreement through the weekend.
Higher resolution models are indicating more precipitation over
the Susitna Valley on Saturday whereas larger scale models are
showing none. In any case, amounts will be low and conditions
overall will remain quiet in the short term.

&&

.AVIATION...

PANC...Fog is expected to persist through this morning. LIFR
conditions are likely, though periods of higher flight categories
are possible as well. MVFR ceilings will generally return this
afternoon as the fog dissipates, however scattered lower clouds
will linger. Light winds will persist.

&&

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

Ridging continues across Southcentral through Saturday night. Low
level moisture trapped under the ridge will continue stratus and
areas of fog across the Kenai Peninsula, Anchorage Bowl, and MAT-SU
Valleys and to a lesser extent the Copper River Basin. Light
southerly flow in the lower levels across Cook Inlet will continue
to strengthen the marine layer and maintain cloud cover and
cooler temperatures across the western Kenai Peninsula, Anchorage
Bowl, and southern MAT-SU Valleys into Saturday. Provided the
cloud cover holds, these areas under the marine influence will
likely not see highs breaking 50 degrees through Saturday. Warmer
temperatures are expected inland. Except for a brief period of
outflow westerly winds near Whittier this morning, winds are
expected to be fairly light over the next couple of days.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 2)...

The longwave pattern features a deep trough over the Bering and
the North Pacific with a ridge over the Gulf. On satellite
imagery, there is a plume of tropical moisture that spans from
the Central Pacific to the Eastern Aleutians and Bristol Bay. The
energy that comes off the North Pacific will follow the path of
least resistance and head directly over SW AK. A wet and foggy
weekend is expected for much of the region with high temperatures
in the mid to upper 40s.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2)...

The longwave pattern features a deep trough over the Bering and
the North Pacific with a ridge over the Gulf. On satellite
imagery, there is a discernible fetch of tropical moisture that
spans from Hawaii to the Eastern Aleutians. There is a mature
frontal boundary with a surface low southwest of Adak that is
producing gale force winds south of the chain. This surface low
will push north, weaken and a new surface low will develop south
of Adak. This combined with a blocking high across the eastern
Gulf spells a continued wet and unsettled period for all of the
Bering Sea and the Aleutians.

&&

Marine Discussion (Days 3 - 5: Sunday through Tuesday)

Bering Sea/Aleutians…
A large area of low pressure in the Bering may produce gale force
winds in the western Bering on Sunday. Confidence is low at this
time as guidance shows different solutions in the placement and
intensity of this low. Forecast confidence remains low for the
remainder of the period as guidance shows differences in the track
and intensity of this low, though winds are expected to remain
less than gale force and no high seas are expected.

Gulf of Alaska...
Forecast confidence remains low at this time due to guidance showing
different solutions in the placement and intensity of synoptic
features. However, winds are expected to remain below gale force
and no high seas are expected.

&&

Long Term Discussion (Days 4 - 8: Monday through Thursday)

Confidence has increased for the long term, as the EC and the GFS
have come into agreement compared to yesterday. The GFS has
strengthened the low similar to the EC and the EC is reflecting
the pattern of the GFS. A strong low will approach the eastern
Aleutians Tuesday remaining nearly stationary through Thursday.
This feature will bring precipitation chances to the western
Bering and Aleutians Monday and to the rest of the Aleutians
through Thursday as it approaches the Gulf. This will nudge the
high pressure over the mainland to the east just slightly
maintaining cool and dry conditions well south of the Brooks Range
through this time period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Fog Advisory: 101 111.
         Flood Watch: 121 (Anchor River).
MARINE...Gale Warning: 170.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...ED/CK