Avalanche Forecast

Archived

Jan 10th, 2012–Jan 11th, 2012

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

South Columbia.

Confidence

Good - -1

Weather Forecast

Mostly clear and dry for the forecast period. Although warmer on Thursday and Friday, freezing levels are expected to remain in or near valley bottoms. Winds are expected to be light but gusty northwesterlies.

Avalanche Summary

Recent observations include several natural storm and wind slab avalanches up to Size 3 in response to moderate precipitation, rising freezing levels and strong winds on Monday. Storm and wind slabs were also sensitive to human triggers on open unsupported 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, but cold temperatures are likely starting to improve storm slab stability. Strong winds have created high variability in treeline and alpine areas, with shallow faceted scoured areas, thick wind slabs, and thin trigger points for various storm snow and persistent weaknesses. Up to three different persistent weaknesses can be found in the top 150cm. The most concerning and deepest is surface hoar and/or facets buried mid-December, which is widespread on all aspects at all elevations, but has been most sensitive on south through east facing treeline slopes. Even though recent snowpack tests have shown that this weakness is getting harder to trigger, it still has a high propensity to propagate fractures and shallower weaknesses create step-down potential.

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.