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Avalanche Forecast

Archived

Jan 25th, 2019–Jan 26th, 2019

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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Anticipated warming could potentially wake up lower weak layers resulting in the potential for large human-triggered avalanches.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Lt Dragon (2380m):Nil; TPres -4, rising rapidly; TMin -10; winds L NWToby Ck (1130m):1cm; TPres -1 rising rapidly; TMin -13KHMR Dogtooth (2060m):Nil; TPres -7, rising slowly; TMin -10KHMR Top (2325m):Winds 20-40 W

Avalanche Summary

One skier-triggered avalanche was reported on Wednesday in storm snow at approximately 2000 m that released 40 cm below the surface. On Thursday, explosive control work released another slide on the deep persistent layer at the base of the snowpack. There is a MIN report from last Saturday that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check out the MIN here. Dealing with the deep persistent basal facet/crust problem requires avoiding terrain where this kind of avalanche is possible.

Snowpack Summary

Up to 20 cm of recent snow has buried large surface hoar crystals which, on southern aspects, may rest on a sun crust. In most places, there is still insufficient snow over this layer and the upper snow too unconsolidated to create a widespread problem. However, locally, in deeper snowpack areas, or where the wind has blown snow above this layer, avalanches large enough to be of concern could be triggered. The snowpack also has a significant weekness at depth. The base of the snowpack is composed of weak faceted grains and a crust in many parts of the region. There have been sporadic reports of people triggering this layer in areas where the snowpack is shallow. The most likely trigger points include ridgelines and large open slopes and bowls at upper elevations, particularly those that have rocky or variable (thin to thick) features. If you trigger a deep persistent slab it will go big and be a highly destructive avalanche.

Problems

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.

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.