Rider triggered avalanches continue to fail on a buried weakness 40-60 cm down. It could be possible to remotely trigger an avalanche from 100-500 m away. Keep it simple, use a conservative approach to terrain.
Confidence
Fair - Due to the number of field observations
Weather Forecast
The dry conditions and sunny skies are coming to an end as a series of pacific frontal systems hit the coast and bring cloudy skies and precipitation through the weekend. Wednesday will be fairly dry and cloudy. Ridgetop winds will be light-moderate from the NW and freezing levels hover around 1500-1800 m. Thursday will bring light snow amounts near 10 cm. Ridgetop winds will blow strong from the SW and freezing levels near 1600 m. Friday will remain cloudy with light precipitation 5-10 mm, and freezing levels rising to 2000 m.
Avalanche Summary
On Monday, the region saw natural slab avalanches up to size 2.5, and numerous remotely triggered avalanches size 1-2.5 from 500 m away. All of the remotely triggered avalanches failed on the mid-February crust buried 30-60 cm below the surface non north-east aspects above 2000 m. This type of fracture character and remote triggering is very unpredictable. A conservative approach and terrain use is required with these conditions.
Snowpack Summary
At higher elevations, new snow up to 60 cm sits over a plethora of surfaces including moist snow, crusts, wind affected surfaces, and/or old wind slabs which may still be reactive especially to rider triggers. Previous rain has saturated the upper snowpack up to around treeline elevations forming a spring-like, melt-freeze crust. In the alpine, strong winds have redistributed the new snow into wind slabs on leeward terrain features. The recent storm snow is sitting over a weak facet/crust layer that was buried in mid-February. This layer has been quite reactive recently and may increase the likelihood of triggering a slab. The late-January crust/surface hoar layer (over 1m deep) and the mid-January surface hoar (around 1.5m deep) have been dormant for several weeks.
Problems
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.
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.