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Avalanche Forecast

Archived

Dec 21st, 2011–Dec 22nd, 2011

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

Regions

South Rockies.

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Thursday: Expect dry conditions with mostly clear skies. Winds should be westerly and reach 40-60 km/h at ridgecrests. Freezing levels may reach 1300m. Friday: Dry conditions persist with continued westerly winds and freezing levels reaching 1500m. Saturday: Winds turn southwest and increase to 60-80km/h at ridgecrest with freezing levels climbing as high as 1800m.

Avalanche Summary

We have isolated reports of shallow slab avalanches affecting the top 20 cm of the snowpack, running on the mid-December surface hoar layer in the northern part of the region.

Snowpack Summary

Westerly winds continue, creating windslabs on lee locations in the alpine and open treeline. A buried layer of surface hoar lies approximately 20 cm below the snow surface. Reports indicate this layer was blown around before it was buried and can only be found in isolated, sheltered locations. A well settled mid pack bridges over the basal weaknesses at the ground. This layer was responsible for some large releases earlier on in the season. However, there hasn't been any activity on this layer since early December and confidence is growing that it is gaining strength.

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.