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Avalanche Forecast

Archived

Jan 7th, 2014–Jan 8th, 2014

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

Confidence

Good

Weather Forecast

Tonight and Wednesday: A weak system will pass through tonight and ease Wednesday morning. Expect light precipitation, Westerly winds switching from the SW with freezing levels at the surface. Thursday: As another system dives South into Washington Wednesday night, the region could see very light to light amount of precipitation early Thursday and then easing off during the day. Winds should be from the W with freezing levels at the surface.Friday: The zonal flow is allowing another system to pass through but quantities are unsure as models do not agree on track and timing of the system. Freezing levels are forecasted to rise.

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

There are pockets of windslab on lee side of SE and SW winds below ridgetop in the alpine. The storm slab is settling but is still sensitive to human trigger, especially where a weak faceted snowpack is underlying that top fresh layer. The facet/crust layer down 80-100 cm at treeline and below treeline  and the depth hoar layer in the alpine seems quite reactive on E aspects. Multiple recent natural and human triggered avalanches on this aspect is 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 test are not as planar as they used to be).  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.