Avalanche Forecast

Issued: Mar 1st, 2017 3:42PM

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

cgarritty, Avalanche Canada

Cariboos.

Wind slabs will continue to grow at the surface while our deep persistent slab lingers, waiting for the right trigger. Conservative terrain selection is key to managing our complex and increasing hazard.

Summary

Confidence

Moderate -

Weather Forecast

Thursday: Cloudy with flurries bringing 5-10 cm of new snow. Winds strong to extreme from the south. Freezing level to 1300 metres with alpine temperatures of -7. Friday: Flurries bringing another 5-10 cm of new snow. Winds moderate to strong from the southwest. Freezing level to 1000 metres with alpine temperatures of -8. Saturday: A mix of sun and cloud with isolated flurries and a trace of new snow. Winds light from the south. Freezing level back to valley bottom with alpine temperatures of -10.

Avalanche Summary

No new avalanches were reported on Tuesday.Many parts of the region have a similar snowpack structure to Clemina Creek, where two size 2 snowmobile triggered persistent slab avalanches were reported on Saturday (see MIN report here). On Monday, another size 2 persistent slab avalanche was accidentally triggered by a skier northwest of Valemount. Nobody was injured in the avalanche which was 50cm deep at the crown and about 120m long. Triggering a large deep persistent slab avalanche is a low probability - high consequence scenario that warrants an extra cautious approach to terrain. See here for a list of recent near misses in the Cariboos and North Rockies.Looking forward, ongoing snowfall and increasing winds on Thursday are expected to promote new wind slab activity at treeline and in the alpine.

Snowpack Summary

About 10-15cm of new snow fell over the region Tuesday night, accompanied (and affected) by strong overnight winds. The new snow has buried faceted surface snow, as well as surface hoar recently reported in sheltered areas in some parts of the region. A thin sun crust may also exist below the new snow on steep solar aspects. About 40cm 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. The reactivity of this layer is unknown, but it's worth keeping an eye on as it gets loaded by more snow. Some lingering surface hoar layers from January are down about a metre 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.

Problems

Wind Slabs

New snow and extreme southwesterly winds on Thursday are expected to form reactive new wind slabs at treeline and in the alpine. The best and safest riding may be in sheltered, lower elevation terrain.

Be cautious as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use ridges or ribs to avoid pockets of wind loaded snow.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Deep Persistent Slabs

A weak layer of facets near the bottom of the snowpack continues to surprise backcountry travelers. This potentially destructive layer deserves respect, and seems most reactive in shallow snowpack areas.

Avoid lingering in runout zones.Be aware of the potential for large, deep avalanches due to the presence of buried weak layers.Carefully evaluate and use caution around thin snowpack areas.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Mar 2nd, 2017 2:00PM