Macdonad West Shoulder

Triggered a size 1-1.5 slab avalanche on the up track of MacDonald West shoulder. No signs of instability prior (no whumpfs or shooting cracks). No skier was caught. Prompted us to stay below tree line and avoid steeper slopes for the rest of the day. The slab released on what could be the rain crust extending higher than expected, or a solar crust layer. The failure was not on the persistent layer.