Avalanche control on Mt. Dennis produced large avalanches that ran over the ice climbs and crossed the Field Back Road. Be very careful at treeline in Little Yoho. Natural avalanches are unlikely but human triggered avalanches are likely.
Weather Forecast
The ridge of high pressure is breaking down and a Pacific storm will cross the region starting Wednesday afternoon. Wednesday itself will be colder (-4 to -10) with winds picking up from the west and snow starting in the afternoon. Expect up to 15 cm by the end of the storm on Thursday afternoon.
Snowpack Summary
Recent warm temperatures aloft have settled the upper snowpack, with suncrust formed on S and W aspects. 30-50cm of snow sits over the Dec.15 persistent weak layer of facets and surface hoar. We are concerned about this layer at treeline in Little Yoho where the layer is producing easy to moderate snowpack test results and widespread whumphing.
Avalanche Summary
Tuesday's avalanche control on Mt. Dennis (above the ice climbs) produced large (size 3) avalanches running over the popular ice climbs with debris and trees reaching the Field Back Road. These were the largest results from a 2-day, park wide avalanche control mission which confirms our suspicion of dangerous conditions at treeline in Little Yoho.
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.