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Avalanche Forecast

Archived

Mar 12th, 2021–Mar 13th, 2021

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, 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.

Regions

Kootenay Boundary.

Rising freezing levels and sunshine will increase the likelihood of avalanches. Avoid exposure to cornices and steep sun-exposed slopes. 

There is uncertainty about whether warming may wake up deeply buried weak layers, and uncertainty is best managed with conservative terrain.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

FRIDAY NIGHT - Mainly clear / light northwest wind / alpine low temperature near -2 / freezing level 1500 m 

SATURDAY - Mainly sunny / light to moderate southwest wind / alpine high temperature near 2 / freezing level 2600 m 

SUNDAY - Mainly sunny with increasing cloud in the afternoon / moderate to strong south wind / alpine high temperature near 1 / freezing level 2300 m 

MONDAY - Mainly cloudy with sunny breaks / light northeast wind / alpine high temperature near -1 / freezing level 2100 m

Avalanche Summary

Rising freezing levels and sunshine will increase the likelihood of avalanches and cornice failures on Saturday. The potential for persistent slab avalanches may also increase with this weather pattern.

Reports from this week have mostly been limited to small wet loose avalanches on solar aspects, and small dry loose avalanches in steep, shaded terrain

During last week's warm weather, a large (size 2) slab avalanche released naturally on a weak layer of facets near the ground in a shallow snowpack area east of the region near Apex.

The most recent avalanche observed on the late January persistent weak layer was reported February 28th, when large explosives produced very large (size 2-3) results at Kootenay Pass.

Snowpack Summary

Wind slabs may be found in lee features at upper elevations. Soft, dry snow exists in sheltered, shaded areas. Solar aspects have a crust on the surface, which will become moist/wet with exposure to sunshine and rising freezing levels.

Deeper in the snowpack, a persistent weak layer from late January is buried 80-150 cm deep and is composed of a combination of surface hoar, crusts, and facets. There is some uncertainty about whether or not this problem will become reactive with rising freezing levels and solar radiation. 

As described in this MIN report, shallow snowpack areas in the east of the region may harbor a faceted basal snowpack. This structure can typically be managed by avoiding shallow rocky areas where the snowpack transitions from thick to thin.

Terrain and Travel

  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
  • Minimize your exposure time below cornices.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

Problems

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.

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.