Numerous large persistent slab avalanches have been triggered by riders this past week. Additional snow and wind Friday night will increase the likelihood of triggering large slab avalanches.
Conservative terrain selection is critical, choose only well-supported, low-consequence lines.
Buried layers from late March reached a tipping point and recently became reactive.
The primary concern is a layer of facets and surface hoar buried 50-90 cm on shaded slopes. On other slopes, this layer is a crust with facets above. Avoid steep open slopes capable of producing large avalanches.
10-20 cm of forecast snow and strong south wind Friday night are expected to form fresh storm slabs and increase the likelihood of triggering large persistent slab avalanches at treeline and above.
No new avalanches were reported on Thursday.
Two persistent slab avalanches were reported northwest of Terrace on Wednesday. A skier triggered size 2 on a north aspect in the alpine and a size 2.5 on an east aspect in the alpine that was triggered by solar radiation. Both failed on a layer of weak facets and/or surface hoar down 40-50 cm.
A fatal avalanche occurred north of Stewart on Tuesday. It was a skier-triggered size 3 persistent slab avalanche that occurred on a northeast aspect in the alpine.
Two additional skier-triggered size 2-2.5 persistent slab avalanches were also reported on northerly aspects at treeline and above on Tuesday. The depth of the weak layer was around 60-80 cm.
10-20 cm of forecast snow and strong south wind Friday night are expected to form fresh storm slabs and increase the likelihood of triggering large persistent slab avalanches at treeline and above.
A weak layer buried at the end of March sits 50-90 cm deep in most areas. It includes facets and surface hoar in shaded areas, and a melt-freeze crust elsewhere. Numerous human triggered persistent slab avalanches have occurred on this layer this week.
The mid and lower snowpack are considered generally strong and well-bonded. In the far northern reaches of the region, basal facets may exist which are currently considered inactive. This layer may become active with abrupt changes to the snowpack, such as rapid loading (heavy snowfall or rain) or prolonged warming.
Friday Night
Snow; 5-20 cm / 60 km/h south ridgetop wind / Temperature at treeline around -4 C / Freezing level 900 m
Saturday
Mostly cloudy with flurries; 3-15 cm / 30 km/h south ridgetop wind / Temperature at treeline around -4 C / Freezing level 1100 m
Sunday
Cloudy with flurries; 3-10 cm / 25 km/h south ridgetop wind / Temperature at treeline around -4 C / Freezing level 1100 m
Monday
Mostly sunny / 20 km/h southeast ridgetop wind / Temperature at treeline around -3 C / Freezing level 1200 m
More details can be found in the Mountain Weather Forecast.
