Avalanche Forecast

Issued: Mar 5th, 2017 3:55PM

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

Avalanche Canada cgarritty, Avalanche Canada

We're entering a period of uncertainty as storm slabs gradually settle and bond to the surface. Avoid pushing into aggressive terrain, especially while the risk of triggering a deep persistent slab is heightened.

Summary

Confidence

Moderate -

Weather Forecast

Monday: Mainly cloudy with isolated flurries and a trace to 5 cm of new snow. Light southerly winds. Alpine temperatures of -12. Tuesday: Mainly cloudy with isolated flurries and a trace of new snow. Light to moderate southeast winds. Alpine temperatures of -13. Wednesday: Mainly cloudy with scattered flurries and up to 5 cm of new snow. Light variable winds. Alpine temperatures of -14.

Avalanche Summary

Reports from Saturday include numerous observations of storm slabs running Size 1.5-2.5 on all aspects, with several running to Size 3. Crown fractures averaged about 40 cm but were noted as deep as 80 cm in presumably wind loaded areas. All of these ran naturally. Backcountry users in the Cariboos should be aware that many parts of the region have a similar snowpack structure to the Clemina Creek area, where two size 2 snowmobile triggered persistent slab avalanches were reported last Saturday (see MIN report here). Last Monday, another size 2 persistent slab avalanche was accidentally triggered by a skier northwest of Valemount. Triggering a large deep persistent slab avalanche is an ongoing low probability - high consequence problem that demands an extra cautious approach to terrain selection in our region. See here for a list of recent near misses in the region.Looking forward, expect a decline in natural avalanche activity while human triggering potential to the full depth of our recent snow accumulation persists for a few more days. Backcountry users should also keep in mind the ongoing potential for smaller avalanches to trigger deep instabilities.

Snowpack Summary

Just under a week of stormy weather has blanketed the region in 45-70 cm of new snow. The snowfall was accompanied by moderate to strong southerly winds, which promoted the formation of touchy storm slabs at upper elevations. The new snow has buried faceted surface snow, thin sun crust on steep solar aspects, as well as surface hoar reported in sheltered areas in some parts of the region previous to the storm. About 75-100 cm below the surface you'll likely find the mid-February interface, which is composed of a thick rain crust up to about 1700 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. Recent reports have suggested greater reactivity on this layer at lower elevations where the rain crust is more prominent. Professionals in the region have also warned that a 'threshold load' has been reached above this interface, particularly where it presents as a crust. Some lingering surface hoar layers from January are now down a metre or slightly more and the weak mid-December facets are down about 1.5 metres. These deep persistent weaknesses still have the potential to react to human triggers or smaller storm slab avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs
As natural avalanche activity subsides, potential for human triggering storm slabs will persist. The touchiest conditions have been reported in wind affected areas and where the new snow overlies crust. (Steep south-facing slopes and below treeline)
Use ridges or ribs to avoid pockets of wind loaded snow.If triggered, the storm slabs may step down to deeper layers resulting in large avalanches.Be alert to conditions that change with elevation.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
A weak layer of facets is lingering near the base of the snowpack. The risk of triggering a deeper weak layer will be heightened while overlying storm slabs remain sensitive to human triggering. The greatest risk exists in shallow snowpack areas.
Avoid or use extreme caution around thin snowpack areas.Avoid lingering in runout zones.Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Mar 6th, 2017 2:00PM