Lizard-Flathead

We have uncertainty around the reactivity of a buried weak layer that produced large rider-triggered avalanches last weekend. Keep your terrain choices conservative and be prepared to back off quickly if you find signs of instability like whumpfing, shooting cracks and recent avalanches. Read our latest blog for advice on how to manage a persistent slab problem.

On Sunday, several large (size 2-3) persistent slab avalanches were reported. They were remotely triggered by skiers or snowmobiles at treeline elevations. Check out these MIN reports here and here. A huge thank you to the groups who shared their observations to the Mountain Information Network!

Since then, avalanche observations have been limited to small explosive-triggered wind slabs.

A dusting of snow sits over a thin sun crust on south aspects, and surface hoar at treeline and below. 30-50 cm of recent snow has been redistributed by previous winds at upper elevations. This recent snow may overlie surface hoar in wind sheltered areas.

A concerning weak layer consisting of facets and surface hoar formed in November is now buried 80-90 cm deep. At the bottom of the snowpack, a thick crust sits on the ground.

At treeline, snowpack depths vary from 120 to 200 cm.

Wednesday night

Partly cloudy. Light northerly wind. Alpine low -13 C.

Thursday

Mostly sunny. Light northerly wind. Alpine high -7 C.

Friday

Mix of sun and cloud. Ridgetop wind increasing to moderate northwest as a cold front passes through. Alpine high -11 C.

Saturday

Mostly cloudy. Light to moderate westerly wind. Alpine high -9 C.

More details can be found in the Mountain Weather Forecast.

• Even brief periods of direct sun could produce natural avalanches.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
• Remote triggering is a concern, watch out for adjacent and overhead slopes.
• The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.