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Avalanche Forecast

Archived

Jan 9th, 2014–Jan 10th, 2014

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

Regions

South Rockies.

Confidence

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

Weather Forecast

Friday:  5 to 10 cm of precipitation for Friday, winds from the west up to 50 km/h with freezing levels rising to 1000 m.Saturday:  10 to 20 cm of precipitation, strong southwesterly winds, freezing level may rise to 1300 m as a pacific frontal system moves through the rockies.Sunday:  Isolated flurries in the wake of the storm system, freezing levels drop to valley bottom, continued strong winds from the southwest.

Avalanche Summary

Windslabs were triggered by a vehicle and by explosive control in the Eastern part of the region on an E facing aspect slopes. These avalanches were up to 1.5 in size and would have slid on older faceted surface or on low density new snow. A detailed incident report about the Corbin area near miss is available here.

Snowpack Summary

Windslabs continue to develop on lee slopes at ridge tops and in the alpine. The recent storm slabs are settling but may still be sensitive to human triggers, especially where a weak faceted snowpack is underlying the top  layer. The facet/crust layer down 80-100 cm at treeline and below treeline and the depth hoar layer in the alpine has been  reactive on E aspects. Recent natural and human triggered avalanches on this aspect are a good sign of this instability. When tested and observed, the surface hoar layer down 70 cm is showing signs of healing (grains are rounding and snowpack tests are not as planar as they have been previously). The South Rockies field team has posted a new blog with some good info and pictures about the recent avalanche incident and about current conditions. Click here to read it.

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.