Avalanche Forecast

Issued: Mar 16th, 2015 9:27AM

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

swerner, Avalanche Canada

Cariboos.

Lingering instabilities will provide tricky conditions in the alpine, especially with the effects of solar radiation. Use a conservative approach to travel and avoid wind-loaded features.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

On Tuesday, a weak front will move onto the coast bringing generally light precipitation to Interior regions later Tuesday night. Ridgetop winds will blow light-moderate from the E-SE and freezing levels will range from 1500-1800 m. Wednesday will see mainly cloudy skies with light convective precipitation which will continue through midday. Ridgetop winds will be light from the NW with freezing levels near 1600 m. On Thursday, a strong front will approach the North Coast and move inland bringing precipitation amounts to the Interior regions anywhere from 2-10 mm. Ridgetop winds will be strong from the SW and freezing levels will hover around 1500 m.

Avalanche Summary

On Sunday, reports of numerous size 1-3 natural slab avalanches and skier remote avalanches were observed. Many of these larger events started as wind and storm slab avalanches from upper elevation start zones and entrained moist snow at lower elevations, running to valley bottoms. These avalanches have occurred on a variety of aspects with northerly aspects being most reactive. These have initiated from 2000-2300 m in elevation. Most of these failures have been on a weak storm shear. I suspect that the deeper releases are occurring on the mid-February layer down 30-70cm.

Snowpack Summary

At higher elevations, new snow sits over a plethora of surfaces including moist snow, crusts, wind affected surfaces, and/or old wind slabs which may still be reactive especially to rider triggers. Rain has soaked the upper snowpack to around treeline elevation. In the alpine, strong winds during the storm have redistributed the new snow into wind slabs in leeward terrain features. Prior to the storm, 30-50cm of snow was sitting over a weak facet/crust layer that was buried in mid-February. This layer has been quite reactive recently and may increase the likelihood of triggering a storm slab. The late-January crust/surface hoar layer (over 1m deep) and the mid-January surface hoar (around 1.5m deep) have been dormant for several weeks.

Problems

Wind Slabs

Thick touchy wind slabs sit over a weakness from mid-February and is reactive to natural and to human-triggering on all aspects. Remote triggering from a distance is possible, and conservative terrain selection is recommended.

Avoid freshly wind loaded features.>Remote triggering is a concern, watch out for adjacent slopes.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 5

Cornices

Looming cornices are weak. Solar radiation and daytime warming could promote cornice failure which could trigger larger slab avalanches from the slopes below.

Give cornices a wide berth when travelling on or below ridges.>Watch for changing conditions with daytime warming and solar radiation. Obvious clues are natural avalanche activity, moist and wet snow surfaces and snowballing.>

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Mar 17th, 2015 2:00PM