Regions
Northwest Inland.
Caution if the sun comes out - avoid steep sunny slopes where the snow will lose cohesion.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
THURSDAY: Mix of sun and cloud with flurries possible. Freezing level at valley floor. Light winds.FRIDAY: 2-5 cm snow. Freezing level near 500 m. Moderate to strong west to south-westerly winds. SATURDAY: Light snow. Freezing level near 300 m. Light winds.
Avalanche Summary
A widespread wind slab cycle was reported last weekend. Following the cycle, a few naturally and human-triggered size 1-2 avalanches have continued over the last few days. Most of these have been confined to recently built wind slabs, however a couple failed on deeper weak layers in the snowpack, especially when triggered from thin spots on a slope.It will still be possible to trigger a wind slab with the weight of a person in specific terrain. Persistent slabs could still be triggered from thin-to-thick snowpack areas, or with a heavy load. Be mindful of any steep slopes getting cooked by the sun and give these a healthy berth.
Snowpack Summary
You're likely to encounter highly variable snow surfaces after recent strong arctic outflow winds took out their fury on the upper snowpack. Fragile cornices and hard and soft wind slabs can be found on many alpine and treeline slopes. Ongoing cold temperatures are helping to break down and soften these. Windward slopes (roughly north to east facing) have been scoured back to an old crust. The wind slabs sit on various old surfaces including sun crusts, facets and spotty surface hoar (which is most prevalent in sheltered treed locations). Around 50-150 cm down, you'll find a crust/surface hoar layer from mid-January, which still has the chance to surprise you and could be triggered from a thin snowpack spot, or with a large trigger like cornice fall. Facets at the base of the snowpack can possibly be triggered from shallow snowpack areas.
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.