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Avalanche Forecast

Archived

Feb 12th, 2013–Feb 13th, 2013

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

Purcells.

Confidence

Fair

Weather Forecast

Wednesday: Light snow early then a mix of sun and cloud. The freezing level is around 1200 m. Winds are light to moderate from the northwest. Thursday: A mix of sun and cloud. The freezing level is near valley bottom. Winds are light from the northwest. Friday: A mix of sun and cloud. The freezing level could jump as high as 1400 m. Winds are light to moderate from the southwest.

Avalanche Summary

There was one new report of a accidentally triggered size 2 slab avalanche from the Dogtooth Range. This slide was triggered on a west aspect in the alpine. It released on a layer of faceted snow overlying a melt-freeze crust (Jan 23 interface) approximately 40-50 cm deep. There were also few natural cornice triggered slab avalanches up to size 2.

Snowpack Summary

The snow surface consists of new wind slab in exposed alpine terrain, a sun crust on solar aspects, and surface hoar and/or facets on shady slopes - all getting dusted by new snow on Tuesday. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm (Jan 23 interface). One recent snowpack test from the Dogtooth Range on a west aspect in the alpine gave moderate "pops" results and showed potential for propagation on a this facet/crust layer. Continued freezing temperatures overnight have helped to strengthen the snowpack at lower elevations.The mid-pack is generally well settled and the average snowpack depth at treeline elevations is near 130. Cornices have grown and may threaten slopes below.

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.