A touchy persistent slab problem demands respect. Use extra caution in your terrain selection.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Generally benign weather is expected for the next three days. Overnight Monday: 5-10 cm snow; Tuesday/ Wednesday: flurries; Thursday: 5-10 cm. The freezing level drops to valley floor late on Tuesday. For more details check out https://avalanche.ca/weather.
Avalanche Summary
Initial reports from Monday suggest a very sensitive persistent slab now exists in the Valemount area. A size 2.5 avalanche failed naturally, and skiers triggered wind loaded slopes at around 2100 m, which failed on the buried surface hoar. Skiers also remotely triggered a slab from 50 m away at 1300 m.In other areas, the persistent slab is also very easy to trigger where it is sitting on a widespread layer of surface hoar. We had a recent report from the Wells Grey area of a skier remotely triggering a size 2 avalanche that was 35 cm deep from 20 m away. This avalanche was 80 m wide and released on buried surface hoar in the alpine. This group also reported numerous whumpfs during the day.
Snowpack Summary
20-50 cm of recent storm snow has now formed a reactive slab over a volatile layer of buried surface hoar. The buried surface hoar may be most prevalent at and below treeline. The slab is likely to be especially reactive where it has gained cohesion through wind pressing, warming, and/or settlement. In general, the mid and lower snowpack are strong with any weak layers considered dormant for now. Snowpack depths are variable and shallow snowpack areas may have weak facetted crystals near the ground.
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.