Avalanche Forecast

Issued: Jan 10th, 2012 8:58AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs, Persistent Slabs and Deep Persistent Slabs.

ccampbell, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Mostly clear and dry for the forecast period. Although warmer on Thursday and Friday, freezing levels are expected to remain in or near valley bottoms. Winds are expected to be light but gusty northwesterlies.

Avalanche Summary

A skier was killed in a Size 3 avalanche in the Dogtooth range near Golden on Friday. The 4th skier on the slope triggered the slide. On Saturday a skier triggered another Size 3 persistent slab avalanche in the Quartz Creek alpine, the crown averaged 100cm in depth & the avalanche was reported to have run full path. The group had been skiing in the area all day without result until the avalanche happened. Avalanche activity on Sunday was confined to operational explosive use & produced avalanches to Size 2 on high elevation NE facing slopes.

Snowpack Summary

Warm temperatures and light to moderate precipitation settled the 40-60cm of recent storm snow and created upside down slabs and/or thin surface crust on Monday. Since then, light amounts dry snow is maintaining the snow supply for wind slab development, but cold temperatures are likely starting to improve storm slab stability. Touchy mid-December surface hoar and basal facets remain a persistent problem. Recent snowpack tests produced easy results that show a high propensity to propagate fractures. When combined with weak wind slabs, thin trigger points, other weaknesses within and under the recent storm snow, the result is a highly variable snowpack with the potential for deep slab avalanches, especially from heavy, thin spot, and/or step-down triggers.

Problems

Wind Slabs

Weak wind slabs are lurking below ridgecrests, behind terrain features and in cross-loaded gullies. Hard drum-like wind slabs often have the potential to release well above the trigger point.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Persistent Slabs

Most concerning on steep, unsupported, open but sheltered, treeline slopes.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

3 - 7

Deep Persistent Slabs

Susceptible to human triggers particularly from thin slab spots on variable slopes, heavy impacts, or deep penetration, such as sled tracks trenching. Slabs are likely to release across entire bowls producing highly destructive avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

4 - 7

Valid until: Jan 11th, 2012 8:00AM