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Avalanche Forecast

Archived

Jan 11th, 2012–Jan 12th, 2012

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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Thursday: Dry and clear, with freezing levels near valley bottoms and moderate northwesterly winds. Friday: Increasing cloud in the afternoon with freezing levels briefly rising as high as 1500m. Saturday: Light snowfall with freezing levels around 900m.

Avalanche Summary

Recent observations include several natural small wind slab avalanches releasing from pockets below cliffs and gully walls, as well as a small skier-triggered wind slab avalanche on a cross-loaded feature. Operational explosive control produced slabs avalanches up to Size 2.5 on north and east facing alpine slopes.

Snowpack Summary

Warm temperatures and light to moderate precipitation settled the 30-70cm of recent storm snow and created upside down slabs and/or thin surface crust on Monday.Since then, light amounts dry snow is maintaining the snow supply for wind slab development, cold temperatures are likely starting to improve storm slab stability, and surface hoar is growing. Strong winds have created high variability in treeline and alpine areas, with shallow faceted scoured areas, thick wind slabs, and thin trigger points. Avalanche professionals are gaining confidence in the mid-December persistent weakness, now down 90-170cm, but concern for human triggers remains on steep unsupported slopes. Furthermore, when this persistent weaknesses is combined with weak wind slabs, thin trigger points, and other weaknesses within and under the recent storm snow and at the base of shallow snowpack areas, the result is a highly variable snowpack with the potential for deep slab avalanches, especially from heavy, thin spot, and/or step-down triggers.

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.