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Avalanche Forecast

Archived

Jan 17th, 2013–Jan 18th, 2013

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

Regions

Kootenay Boundary.

Confidence

Good

Weather Forecast

Friday:  Extreme W ridgetop winds at ridgetop. No precip. Potential above freezing temperatures in the alpine.Saturday:  Strong NW winds at ridgetop. No precip. Potential above freezing temperatures in the alpine.Sunday: Moderate NW winds at ridgetop.  No precip.  Potential above freezing temperatures in the alpine.

Avalanche Summary

Numerous wind slab avalanches to size 2 were reported from NE, E and SE facing slopes Wednesday.  Loose wet avalanches to size 1 were also observed on steep solar aspects.

Snowpack Summary

Recent winds have formed hard slabs, soft slabs and sastrugi in open terrain.  We've recieved reports of hard slabs up to a meter deep in the region. South and West facing slopes have been moistening up during the day with the warm temperatures.  Under the moist snow and windslabs the January 4th layer can be found down 50 - 150 cm.  It consists of small facets, surface hoar (up to 12mm) in sheltered treeline and below treeline areas, and a sun crust on steep solar aspects.  Test pits are still showing resistant planar shears at this interface, but it hasn't been reactive to human triggering for days now.The midpack is well bonded and strong.

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.