Avalanche Forecast

Archived

Dec 5th, 2012–Dec 6th, 2012

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Kootenay Boundary.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Overnight and Thursday: Light snowfall / strong west winds decreasing to moderate and southwest by Thursday / Freezing level at 800mFriday: Light snowfall / moderate to strong southwest winds / Freezing level at surface Saturday: Trace amounts of snow / Light north winds / Freezing level at surface

Avalanche Summary

On Wednesday several natural avalanches to size 2 were reported from the region while explosives control produced isolated releases to size 2.5. These releases which occurred at treeline and above are suspected to have run within recent storm/wind layers or on the late November surface hoar.

Snowpack Summary

Recent snowfall amounts have been highly variable, but in deeper snowpack areas up to 85 cm of settled storm snow has fallen in the past week. This snowfall was accompanied by generally moderate to more recently strong and variable winds, forming deep and reactive wind slabs in exposed leeward terrain. Below the recent storm snow is a layer of surface hoar that was buried at the end of November. This layer continues to be reactive. At the base of the snowpack sits the early November rain crust. This layer seems most likely to be found in deeper snowpack areas at higher elevations. I'm not aware of any activity on this layer as of late, but observations have been limited and it may have the potential to 'wake-up' with continued loading.There are significant variations in snowpack structure from one drainage to another. In short, digging down and making your own observations will be critical to safe slope selection. Thank you to those who have shared field observations with us. If you would like to do the same, you may contact us at [email protected].

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.