Small Craft Advisory 384, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 PM AKDT Sat May 7 2022

.ANALYSIS AND UPPER LEVELS...

The pattern is beginning to shift over the state and that can be
seen in the satellite imagery early this afternoon. The upper level
high pressure is shifting eastward as an unseasonable strong,
cold upper level low is approaching the Bering Strait from the
northwest. This low will be the cause of the cooler weather for
the early part of next week.

The area of convection has shifted eastward with the Copper River
Basin being the main area with convective buildup. There are a few
showers over the central Kenai Peninsula as well as on the
western slopes of the Alaska Range. but the air moving in from the
west is more stable and that will limit shower development and
coverage. The Susitna Valley had stratus overnight and this
cooler and more stable air is delaying any cumulus development
this afternoon. Farther west, the Bering Sea is engulfed in
stratus. This marine stratus has pushed into the Kuskokwim Delta
and is unlikely to clear out today as the air is just too cold and
the westerly marine push is too strong. The only clear area out
of the stratus in the eastern Bering is the very northern section
of Bristol Bay where the stratus is blocked in the northwesterly
flow off the Ahklun and Kilbuck Mountains.

&&

.MODEL DISCUSSION...

Models are in good synoptic agreement through the middle of next
week. Models also all show the main area of convection continuing
to move eastward and into the Yukon by Sunday.

The main forecast challenge remains determining the degree of
cooling in the northwest flow behind the trough on Sunday and
Monday, and whether this cooling will be sufficient for rain
showers moving through with the trough to mix with or change over
to snow. This is most likely for the Kuskokwim Valley, as well as
over the more northern parts of the Susitna Valley and Copper
River Basin.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Tuesday)...

Relatively quiet weather will persist through this weekend before
a pattern change sets up early next week. Ridging will move over
the area Sunday and result in clearer skies and temperatures
reaching the 50s. As the aforementioned ridge moves closer to
the region Sunday afternoon, pressure gradients will tighten and
result in gusty conditions into many of the favorable gaps,
especially the Barren Islands, Whittier, and Kachemak Bay. Fog is
also possible Sunday morning for the valleys as the ridge tracks
over the domain, especially the Susitna Valley and Copper River
Basin.

A strong upper-level trough accompanied by a low will drop from
the north late Sunday into Monday. With this system, cooler
temperatures are anticipated as colder air from the north will
be drawn south as the aforementioned system's cold front sweeps
through the domain. As the front tracks through the area, winds
will ramp up and bring strong westerly winds to many of the
favored areas. As cold air advection takes place, the Barren
Islands will reach gale-force winds Monday before slowly
diminishing mid-week. Expect seas around 15 ft near the Barrens
late Sunday night into Tuesday. Due to the origin of the system,
most of the precipitation is expected to stay along the Alaska
Range and mainly away from population centers, though a few
sprinkles cannot be ruled out. Mountainous regions could see a
couple inches of accumulating snow, especially near Hatcher Pass.

&&

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

The next front is anticipated Sunday morning. Expect another
batch of precipitation with a potential transition to snow
over portions of the Kuskokwim Delta and Lower Kuskokwim Valley
by Sunday night. Total snow accumulations will be minimal in the
valleys and up to 2 inches in the mountains. This is an Arctic
system so expect robust cold air advection (CAA) which will
translate to below normal temperatures for this time of the year
as well. Isolated light precipitation and cool temperatures will
linger into Monday and Tuesday. In fact, the CanSIPS (Canadian
Seasonal and Interannual Prediction System) model has negative
height anomalies over Southwest Alaska the entire month of May.

&&

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

The longwave pattern features a positive tilt ridge over the NW
Pacific/Western Aleutians and a trough over the eastern Gulf Of
Alaska. The jet core is south of the AKPEN with an estimated
magnitude of 155 knots. There is a secondary jet near the Bering
Strait. Expect a surface low to push across the northern Bering
this forecast period and high pressure will set up over the
Aleutians. Gusty winds and showers are expected Sunday from the
Pribilofs and northward. Then mild weather will return to the
northern Bering. Meanwhile for the Aleutians Sunday-Monday low
stratus and areas of fog are possible.

&&

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

An upper trough moving through interior Alaska is expected to
induce lee cyclogenesis near the Kenai Peninsula early next week
with a newly developed area of low pressure translating
southeastward across the east Gulf of Alaska by the middle of the
week. Gales are anticipated through the gaps and passes of the
Alaska Peninsula as a tightened pressure gradient is maintained
between weak high pressure north of the Aleutians, the upper
trough over interior Alaska, and the departing area of low
pressure over the eastern Gulf. Outside of the elevated northerly
flow, however, mild and dry conditions with sub-gales will
prevail over both the Bering and the Gulf of Alaska into Thursday.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through Saturday)

Seasonably dry conditions are forecast during the 4 to 7 day period
with a ridge of building high pressure over the Bering Sea and a
persistent trough of low pressure over the eastern Gulf of Alaska.
Upper level steering flow will keep shortwave activity on a
northwest to southeast trajectory into eastern portions of
Southcentral while the Southwest region and the Bering/Aleutians
will remain beneath a high pressure inversion. Over the Bering,
trapped moisture at the surface may result in areas of widespread
low-level stratus and fog at times but no significant precipitation
is forecast. An absence of disturbances across the Bering will
also keep surface winds at bay into the weekend. Further east and
despite the potential for one or two shortwave troughs to dip
across Southcentral, northerly winds at the surface will bring in
a drier air mass. This will limit precipitation chances across
the Anchorage Bowl and the Mat-Su. The potential for easterly
small craft winds may develop by the end of the week should any
weak easterly waves of low pressure slide across the Gulf coast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch 152.
MARINE...Gale Warning 120 130 131 138 139.
FIRE WEATHER...None.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...NS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...BL