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Avalanche Forecast

Archived

Dec 28th, 2011–Dec 29th, 2011

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

Regions

Kootenay Boundary.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Wednesday night: 10-15cm. Moderate to strong west to south-west winds. Freezing level lowering to 1300m.Thursday: Light snowfall. Light-moderate north-westerlies. Freezing level around 900m.Friday: Moderate to heavy snow. Strong south-west winds. Freezing level around 1000m. Saturday: Light flurries. Cooling temperatures. Light north-westerly winds.

Avalanche Summary

We are now in an avalanche cycle with numerous natural and human-triggered avalanches occurring, reported as up to size 2.5. Many of these are failing on the mid-December surface hoar, mostly on north through east aspects from 1500m to the peaks. A skier remotely triggered an avalanche from 50m away and in many places shooting cracks and whumphing are further indicators of a very touchy, unstable snowpack.

Snowpack Summary

The snowpack is in a very touchy state. 30-50cm of storm snow has built up over a weak old snow surface. The storm snow has turned into a soft slab due to warming. South-west winds have led to the development of wind slabs on lee slopes. The surface hoar layer buried in mid-December is now under 45-70cm of snow and is highly reactive. It is well-preserved with 10-15mm crystals and exists into alpine start zones (although it's probably best preserved in sheltered areas near treeline). The mid-pack is generally well settled. Facets exist at the base of the snowpack.

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.

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.