The possibility of a large persistent slab avalanche means continuing to avoid large, steep, open slopes.
These avalanches may be hard to trigger, but the consequences would be serious.
Some natural wind slab activity was noted on Wednesday, and human triggering remains possible. There is also loose snow available for transport, so fresh, reactive wind slabs have the potential to form.
A layer of weak, sugary snow surrounding a firm crust is buried 100 to 200 cm deep. Sun and warm temperatures were likely triggers for recent avalanches on this layer. Rocky alpine start zones would be a bad place for a human to be.
Wednesday Night
Partly cloudy. 10 km/h west ridgetop wind, increasing to 30 km/h through the night. Treeline temperature -3 °C. Freezing level 1100 m, possibly dropping to valley bottom for a short period early in the morning.
Thursday
Mix of sun and clouds. 30 km/h west ridgetop wind. Treeline temperature -3 °C. Freezing level 1200 m.
Friday
Mix of sun and clouds. 20 km/h west ridgetop wind. Treeline temperature -3 °C.
Saturday
Mix of sun and clouds. 20 km/h south ridgetop wind. Treeline temperature 2 °C. Freezing level 1600 m.
More details can be found in the Mountain Weather Forecast.
On Wednesday in the Seaton area, our field team saw evidence of a large (size 2.5) naturally triggered persistent slab avalanche on a south facing slope at 1800 m. It ran across the normal trail, and likely occurred on the weekend.
This continues the trend of persistent slab avalanches from late last week, including a remotely triggered size 3.
With little change in the weather, we expect that avalanches like these remain possible on all aspects.
10-30 cm of recent snow is settling over a strong, supportive crust that is expected on the surface on all aspects at treeline and on all but north-facing terrain in the alpine.
A possible period of moderate northeast wind may be loading this loose snow onto crusty southwest facing slopes.
A layer of weak, sugary snow over a thick crust is buried 100 to 200 cm and continues to produce large, surprising avalanches.
