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Avalanche Forecast

Archived

Jan 31st, 2020–Feb 1st, 2020

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

Intense snowfall, strong wind, and warming temperatures are creating dangerous avalanche conditions that warrant wide terrain margins. Avoid avalanche terrain and overhead exposure on Saturday.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

Friday: Cloudy, 10-20 cm snow transitioning to rain below about 1900 meters, moderate to strong southwest winds, alpine temperatures reaching +1 C as freezing levels climb to 2100 meters.

Saturday: Cloudy, 10-20 cm of snow, rain below about 1800 meters, moderate southwest winds, becoming strong at ridge-top, alpine temperatures around 0 C with freezing levels beginning to fall from 2000 meters in the afternoon.

Sunday: Mostly clear, light southwest winds, alpine high temperatures around -8 C, freezing level at valley bottom.

Monday: Partly cloudy, light northwest winds, alpine high temperatures -9 C.

Avalanche Summary

Due to continuous stormy weather, there have been daily avalanches reported in the region. Most of these have been storm and wind slab avalanches, up to size 3 but mostly around size 1-2. They have been triggered by humans, explosives, and naturally. These have occurred on all aspects, mainly at treeline and alpine elevations.

Over the past week, there have been several deep persistent slab avalanches reported in the region. Two were triggered by explosives and one that occurred near Golden was remotely triggered by humans. This activity outlines the fact that this layer remains a problem in the region. Large alpine features, especially rocky, thin snowpack areas are the most likely places to trigger this layer. Touchy storm slab avalanches may have the potential to step-down to this layer. Reports also indicate that cornices may be reaching their breaking point and may act as triggers for larger avalanches.

Snowpack Summary

Over the past 2 days, 20-30 cm has fallen at higher elevations. By Saturday afternoon, an additional 20-35 cm is expected to accumulate above 1900 m. Forecast strong winds and warm temperatures will speed up slab formation as new snow accumulates as well as contribute to rapid cornice growth. A large, natural avalanche cycle is expected. Rain is forecast to saturate snow surfaces up to 1900 meters, triggering wet loose avalanches. The hazard from wet loose avalanches will decrease as temperatures cool throughout the day on Saturday.

A weak layer of surface hoar can currently be found about 70 cm deep around Golden and Kimberley, 30 cm deep around Invermere, and 100 cm deep along Kootenay Lake.

As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall or explosives. New snow, rain, and warming will collectively add considerable strain to these weak layers. Their potential to fail naturally and produce large, destructive avalanches will be significantly increased during the storm.

Terrain and Travel

  • Avoid exposure to overhead avalanche terrain during periods of heavy loading from new snow, wind or rain.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.

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.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.