A deeply buried weak layer is still producing large destructive avalanches in isolated areas and may be remotely triggered from a distance. Use extra caution around steep, unsupported alpine terrain.
Confidence
Fair - Due to the number of field observations
Weather Forecast
High pressure persists over the interior for the forecast period. A mix of sun and cloud is expected on Tuesday with treeline temperatures around -8 and light alpine winds. Wednesday and Thursday may see an increase in cloud cover while treeline temperatures should remain around -8 and alpine winds should remain light.
Avalanche Summary
On Monday, explosive control produced a size 3 deep slab avalanche. A report on Sunday of a skier remotely triggering a size 2.5 avalanche from 5 meters away in the Dogtooth range alpine. This occurred at around 2300m in the alpine. Also reported was an explosive triggered size 2 persistent slab releasing around 60cm deep.
Snowpack Summary
A surface crust exists up to around 2200 m. Above this elevation is dry storm snow which is settling out and faceting. A new layer of surface hoar is currently forming on the snow surface. In exposed alpine terrain, strong southerly winds last week may have resulted in variable distribution of the surface snow and the formation of wind slabs. The early November crust/facet layer is down around 1 m. Tests are suggesting that this layer is getting difficult to trigger but still has the potential to produce large avalanches. We received reports that this deep weak layer has resulted in remotely triggered avalanches over the weekend.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.