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Avalanche Forecast

Archived

Feb 8th, 2013–Feb 9th, 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.

Blue skies and fresh snow may tempt you into steeper and bigger terrain. Maintain a diligent approach to terrain selection to best manage the current conditions.

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

A strong ridge of high pressure builds off the coast allowing a cool, dry NorthWest flow over the region with high diurnal variations. Scattered too few clouds will exist allowing some sunny alpine skies on Saturday with more predominant sunny skies on Sunday. Ridgetop winds will blow light-moderate from the NorthWest. Treeline temperatures will hover near -4 and freezing levels rising to 1100 m in the afternoon.

Avalanche Summary

Several small slab avalanches occurred size 1 from steep, cross-loaded terrain features. A skier triggered size 1.5 slab avalanche occurred from a NE aspect at 2300 m. Natural loose dry sluffing continued from steep unsupported terrain.

Snowpack Summary

Wind slabs exist in the alpine and at treeline on lee slopes and behind ridgelines. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm. However, areas that have buried surface hoar seem to be most touchy. Continued freezing temperatures overnight have helped to strengthen the moist surface layers that developed during warm period last weekend. Watch the duration and intensity of the sun in your local riding area; it may weaken the upper snowpack. Cornices have grown and may threaten slopes below. The mid-pack is generally well settled and the average snowpack depth at treeline elevations is near 130 cm.

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.