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Avalanche Forecast

Archived

Dec 15th, 2021–Dec 16th, 2021

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

Regions

North Columbia.

Use extra caution near ridgelines and "thick to thin" areas where the likelihood of triggering avalanches will be greater.

Confidence

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

Weather Forecast

Wednesday night: some light flurries with moderate Southwest winds. Low of -11 at 1500m.

Thursday: light Southwest winds in the morning with some flurries bringing up to 5cm of new snow. Winds will shift to moderate from the Northwest in the alpine. High of -9 at 1500m.

Friday: High of -13 at 1500m. Moderate Northwest winds in the morning shifting to Southwest in the afternoon. Some light flurries in the afternoon.

Saturday: A storm arrives bringing up to 20cm of new snow with strong Southwest winds. High of -10 at 1500m.

Avalanche Summary

On Tuesday explosives triggered numerous storm slab avalanches up to size 1.5 on North and East aspects in terrain between 2200 and 2350m.

Snowpack Summary

10 to 30cm of low density snow fell Tuesday morning with the largest amounts in the Selkirks. This overlies old storm snow that was redistributed by moderate Southeast winds.

  

The defining feature of the snowpack is a widespread crust that reaches as high as 2200 m and now sits 50-100 cm below the surface. In many places overlying snow is well-bonded to the crust but in others weak faceted grains have been observed growing above it. The facets above the crust are most prominent at upper treeline where the crust is thinner.

Average snowpack depth at treeline is 250cm.

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

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.

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.