Avalanche Forecast

Issued: Mar 7th, 2017 4:43PM

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

cam_c, Avalanche Canada

Cariboos.

Storm slabs are primed for people triggering large avalanches, and have the potential to step down to deeper persistent weaknesses resulting in very large and dangerous avalanches.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

WEDNESDAY: Overcast with light winds and convective flurries, some areas may see 5-10 cm of new snow.THURSDAY: Overcast with convective flurries and light easterly winds. Alpine temperatures may be close to -20 in the morning.FRIDAY: Cloudy with 10-15cm of fresh snow accompanied by moderate SW winds. Alpine temperatures reaching -10 C.

Avalanche Summary

Reports from Monday include several natural avalanches up to Size 1.5 out of extreme terrain after brief sun-exposure, and one natural Size 2.5 on a northeast aspect. On Sunday we had one report of a natural cornice fall size 2.0 and a skier accidentally triggered a size 1.0 avalanche. Storm slab avalanches were widespread on Saturday up to size 2.5.

Snowpack Summary

45-70 cm of new snow fell in the past week, which is bonding poorly to faceted snow, thin sun crust on steep southerly aspects, as well as surface hoar in sheltered areas in some parts of the region. The snowfall was accompanied by moderate to strong southerly winds, which promoted the formation of touchy storm slabs at upper elevations. About 75-100 cm below the surface you'll likely find the mid-February persistent weakness, 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

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

Persistent Slabs

Persistent weakness layered throughout the snowpack create the potential for very large step-down avalanches. The risk of triggering a deeper weak layer will be heightened while overlying storm slabs remain sensitive to human triggering.

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

Expected Size

2 - 4

Valid until: Mar 8th, 2017 2:00PM