Backcountry Avalanche advisory 

February 20, 2008

Alpine : Moderate

Treeline : Low

Below Treeline : Low

Travel Advisory : Exposed alpine terrain is widely wind affected. Pleasant spring-like days have left a melt-freeze crust on solar aspects. Cornices have been fragile, so give them a wide berth from both above and below. There have been several reports of cornice failures propagating large slab avalanches in the area. Keep in mind that a surface slab in motion has the potential to step down into older buried weaknesses.

Avalanche Activity : Snowballing and point releases to Size 1.0 have been widespread on solar aspects. Cornices have been very reactive to small triggers, so stay well back. The most recent activity on the Dec. 4 crust and facet layer was on Jan. 21 and was initiated by a large cornice fall.

Snowpack : The strong winds have created a wide variety of conditions in the alpine and treeline terrain. There are extensive areas of stiff windslab in exposed terrain, and areas of less wind affected unconsolidated snow in sheltered terrain. On solar aspects the upper 5-10 centimetres has been through a multiple day melt-freeze cycle. Below the new snow layers are several layers of buried windslab. At treeline and below treeline elevations several surface hoar and facet layers are now buried anywhere from 40-80 cm in depth. Now that these layers have received a critical load there have been reports of whumphing and cracking on some treeline slopes, as well as isolated skier and machine triggered avalanche activity on these buried weaknesses. The Dec. 4 crust and facet layer seems dormant for now, buried deeply within our snowpack in most areas.

Weather : Weak low-pressure systems are expected to bring cloud with mild day time temperatures to our area for a few days. No significant changes are expected through the weekend.

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