Small Craft Advisory 240, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 AM AKDT Thu Mar 12 2020

.ANALYSIS AND UPPER LEVELS...

A low is centered near the Kamchatka Peninsula. Its associated
front is currently tracking across the western Aleutians,
bringing rain and gusty southerly winds to that area this morning.
A ridge encompasses the remainder of the Bering and Southwest
Alaska leading to clear skies and cold temperatures across
interior regions. Cold, dry air likewise remains in place over
Southcentral with northerly gap winds diminishing as low pressure
weakens over the Gulf.

&&

.MODEL DISCUSSION...

The numerical models continue to be in very good agreement. The
high resolution models are preferred due to the better handling of
gap winds. Forecast confidence is above normal.

&&

.AVIATION...

PANC...VFR conditions and generally light northerly winds will
persist.

&&

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

An upper-level trough moving south over the Copper River Basin
this morning will enhance the gusty outflow winds through favored
gaps and passes today. The strongest of these winds will once
again be from eastern Prince William Sound to the Copper River
Delta, including Valdez and Thompson Pass. Winds will quickly
increase early this morning and reach peak intensity mid- morning
through mid-afternoon as the trough departs and the winds both
near the surface and aloft align in a northeasterly direction
ahead of an advancing and strengthening upper-level ridge. A high
wind warning has been issued for Thompson Pass with gusts expected
to reach 75 mph. As the ridge tracks east, the winds will slowly
taper off through the nighttime hours, with calmer conditions
expected beginning Friday and remaining through the weekend.

Mainly clear and dry conditions will also persist as the ridge
builds overhead and becomes the dominant weather feature over
Southcentral. With the ridge in place, the strong northerly flow
responsible for the intrusion of arctic air will shut off as a
weak southerly flow develops, especially over the western half of
Southcentral. This will allow for a gradual warming trend through
the weekend with daytime temperatures climbing to around or
slightly above normal.

&&

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

An upper level ridge beginning to move over Southwest Alaska this
morning will help to keep relatively quiet conditions throughout
the day. Clear skies will persist throughout the day as the
temperatures across the region begin to warm slightly. This upper
level ridge will then move across the southern mainland on
Friday, with a Bering front moving in behind this feature. Most
areas will remain dry through Friday, with areas west of Bethel in
the Kuskokwim Delta Coast likely to see a chance of precipitation
and stronger winds moving in. These areas from Hooper Bay to
Toksook Bay will initially start out as snow as the front edges
over the mainland, but will possibly see a period of mixed
precipitation on Saturday as temperatures warm to near the
freezing mark.

&&

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

A storm force low over the western Bering and Aleutians this
morning will continue its path into the northern Bering through
this evening, with winds diminishing by Friday morning. High
pressure over the southern mainland and Gulf of Alaska will keep
the front from progressing into the eastern Bering and Southwest
Alaska. A band of precipitation will set up over the central
Aleutians and Bering starting tonight and continuing through the
weekend. This warm southerly fetch will bring an ample amount of
moisture to the region, resembling an atmospheric river pattern.
With the ridge holding in place to the east, Dutch Harbor could
see up to 2 inches of rain beginning this evening through late
Saturday. There could be a brief period of snow with little
accumulation initially as the front moves over the area, but this
will quickly transition to all rain as the warmer temperatures
move into the area. Areas along the Alaska Peninsula will see a
chance of snow showers overnight tonight throughout the weekend,
but no significant accumulation is expected as the bulk of
precipitation will stay over the eastern Aleutians.

&&

.MARINE (Days 3 through 5)...

A storm force system over the northern Bering will keep an area
of storm force to high end gale force winds west of Saint Matthew
Island and north of 56N on Thursday. By Friday, this system will
have weakened, but enhanced winds and rough seas are still
anticipated into Saturday. Shifting to the North Pacific, a low
will approach the central and eastern Aleutians Thursday night,
bringing the next round of precipitation to the eastern Aleutians,
including Dutch Harbor, through Friday night. A ridge will set up
over the Gulf of Alaska and mainland. Once this ridge gets
established, the active corridor for low tracks will be the NW
Pacific to the western Bering.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The global models continue to bring a high amplitude ridge into
the Gulf of Alaska and Southcentral. This will keep clear skies
and dry weather over most of southcentral Alaska. However, the
weather will be active over the western/central Aleutians and
western/central Bering. With the block in place over Southcentral,
the lows will follow the path of least resistance. The ridge
remains steadfast through Tuesday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 131.
MARINE...Heavy Freezing Spray Warning: 119 121 129 130 165.
         Storm Warning: 185.
         Gale Warning: 121 127 128 165 170 172 177 178
FIRE WEATHER...NONE.

&&

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