Avalanche in Alaska, June 22, 2024

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
438 AM AKDT Sat Jun 22 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Today through Monday night)...

The forecast remains mostly on track for the next couple days
across Southcentral Alaska. Today will feature a ridge building
overhead and a warming trend. High temperatures will generally
range from the upper 60s along the coast to 70s and 80s inland.
The warming for inland locations such as the Copper River Basin
and Susitna Valley will be driven by gusty northerly winds. These
winds will also help to lower relative humidities. As such, a Red
Flag Warning remains in effect through today for those areas.

The complication to the forecast will be the coverage of
convection in the presence of the ridge building overhead.
Although unstable, the valleys/lower terrain of the Susitna,
Copper Basin, Anchorage, and Kenai Peninsula look to remain mostly
dry today due to the descending air associated with the ridge.
The better chances for showers and storms look to be along the
foothills of the higher terrain. However, storm motion looks to be
light and out of the northeast, so any storm that does form along
the mountains could advect into the valleys. The question
remains, if storms do advect into the valleys, can they hold
together with relatively drier air in place at the surface, albeit
unstable air.

The story remains mostly the same for Sunday concerning
thunderstorms. The only exception is that temperatures should be a
bit lower than today and relative humidities should be a tick
higher. The only exception is the Copper Basin which will remain
pretty dry for Sunday but with lower winds. By Monday, ridge axis
moves eastward toward the ALCAN border with continued warm
temperatures expected. Guidance is still having a tough time
figuring out if a wave from the west will move over the area or
not. While diurnal convection is still anticipated, there is still
moderate uncertainty if the storms will become more organized or
not.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS
(Days 1 through 3: This morning through Tuesday morning)...

The big picture of the forecast remains largely unchanged, though
there continue to be updates to the precipitation and
thunderstorm forecast for Southwest Alaska. Expect thunderstorm
chances to persist through the weekend for Southwest Alaska, along
with a general warming trend. For the Bering Sea and Aleutian
Islands, most areas will see light winds less than 25 kt except
for coastal marine zones south of the Central Aleutians, which
will experience winds to small craft speed as a weak low skirts
south of the Aleutians. Model agreement remains poor beyond
Monday as models struggle with the track of an approaching weak
North Pacific low.

Diving into the details... rain showers and isolated to scattered
thunderstorms revisit Southwest Alaska this afternoon and
evening, north to south, mainly on the west side of the Alaska
Range. Today's convection looks to be a bit more robust than
yesterday's, so expect a little more lightning and rainfall.

Thunderstorm chances continue through Monday, with forecast
confidence slowly improving. Thunderstorms could move out onto
the coastal waters of Bristol Bay south and east from Dillingham,
so mariners are advised to monitor the forecast for updates.

Concerning model uncertainty, there continue to be differences in
the projected track of a weak, North Pacific low approaching the
Western and Central Aleutians on Monday. The biggest change with
this forecast package was to delay the onset of stronger winds and
the onset of rain. The forecast may continue to shift as models
better focus on this low. Regardless, this weak storm system is
unlikely to have major impacts on the Western and Central
Aleutians.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...

A very dynamic weather pattern is continuing to develop across
the region. A low over the Sea of Okhotsk, with associated fronts,
will track slowly eastward and weaken as it approaches the
Western Aleutians producing showers and gusty winds along its
path. Its upper level low will merge with the long wave trough
that stretches back over the Bearing Sea and into the Kamchatka
Peninsula. A North Pacific low south of the Aleutian Islands will
slowly progress towards the east and slowly strengthen as it
approaches the Gulf of Alaska. This system has the potential of
producing locally heavy precip and gusty winds in Western Alaska,
Bristol Bay and the Eastern Aleutians. Models are in fairly good
agreement in the short term but diverge greatly as the GFS keeps
the system south of the Eastern Aleutians and ECWMF speeds things
up and has the system centered over Bristol Bay by the end of the
period.

A well developed low the Northeast Pacific and associated fronts
continues to track towards the east and front spreads locally
heavy rain and gusty surface winds less than gale force across the
region and into coastal Canada with the system dissipating early
Thursday.

-Kutz/Dellinger

&&

.AVIATION...

PANC...VFR conditions will continue to persist through the TAF
period. Light and variable winds this morning will become more
southerly during the afternoon hours. Southerly winds return to a
more light and variable regime tonight and into Sunday morning.

The forecast remains on track for the vast majority of showers
and convection to remain north of the area in the vicinity of the
high terrain of the Matanuska Valley and Copper River Basin.
However, there is a possibility that a shower or two and even a
storm could make it off the high terrain of the Chugach Mountains
and in the vicinity of Anchorage. Confidence and probability
remains low regarding this though. Any showers and thunderstorms
that do develop will die down overnight with the loss of day-time
heating and instability.

&&