Avalanche Forecast

Issued: Mar 17th, 2015 9:29AM

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

Avalanche Canada swerner, Avalanche Canada

Rider triggered avalanches continue to fail on a buried weakness 40-60 cm down. It could be possible to remotely trigger an avalanche from 100-500 m away. Keep it simple, use a conservative approach to terrain.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

The dry conditions and sunny skies are coming to an end as a series of pacific frontal systems hit the coast and bring cloudy skies and precipitation through the weekend. Wednesday will be fairly dry and cloudy. Ridgetop winds will be light-moderate from the NW and freezing levels hover around 1500-1800 m. Thursday will bring light snow amounts near 10 cm. Ridgetop winds will blow strong from the SW and freezing levels near 1600 m. Friday will remain cloudy with light precipitation 5-10 mm, and freezing levels rising to 2000 m.

Avalanche Summary

On Monday, the region saw natural slab avalanches up to size 2.5, and numerous remotely triggered avalanches size 1-2.5 from 500 m away. All of the remotely triggered avalanches failed on the mid-February crust buried 30-60 cm below the surface non north-east aspects above 2000 m. This type of fracture character and remote triggering is very unpredictable. A conservative approach and terrain use is required with these conditions.

Snowpack Summary

At higher elevations, new snow up to 60 cm 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. Previous rain has saturated the upper snowpack up to around treeline elevations forming a spring-like, melt-freeze crust. In the alpine, strong winds have redistributed the new snow into wind slabs on leeward terrain features. The recent storm snow is 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 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

An icon showing 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.  Weak cornices could trigger slabs from slopes below.
Avoid freshly wind loaded features.>Give cornices a wide berth when travelling on or below ridges.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

An icon showing Persistent Slabs
A persistent weak interface buried mid- February 30-60 cm below the surface is responsible for numerous large slab avalanches. Remote triggering from a distance is possible, and conservative terrain selection is recommended.
Be aware of the potential for wide propagations.>Remote triggering is a concern anywhere from 100-500 m away, watch out for adjacent slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Valid until: Mar 18th, 2015 2:00PM