The widespread Natural activity that we have seen this week should start to diminish as the last of the storms pass. Human triggering will continue to be likely and conservative travel is advised. The CAC has posted SPECIAL PUBLIC AVALANCHE WARNING.
Weather Forecast
The system over Waterton will pass overnight leaving another 10cm with moderate West winds. Small amounts of snow are expected Friday as the winds start to shift NW and temperatures begin to drop. Light North winds for Saturday with some flurries as the temperatures continue to drop. Expect -20 C for Monday with very light winds and blue skys.
Snowpack Summary
Up to 100 cm now buries a significant weak layer found on all aspects and at all elevations. Gusty West winds and mild temperatures have contributed to widespread slab formation especially in open areas. More loading and wind will increase the serious nature of these persistent slabs. Weak snow at the base of the snowpack also remains a concern.
Avalanche Summary
Widespread natural activity occurred though the week with many large events flattening trees. Most significant paths ran. One sz 3.5 avalanche was confirmed to have stepped down to the November facets and this is suspected to have occurred in some of the many other sz 3 events which ran full path. Impressive propagations and remote triggering seen.
Confidence
Due to the number of field observations
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.