Avalanche Forecast

Cariboos

Date issued

Jan 11, 2018 - 4:51 PM

Valid until

Jan 12, 2018 - 2:00 PM

Prepared by

cgarritty

Very dangerous avalanche conditions have developed in the Cariboos - especially in the south of the region.

A Special Public Avalanche Warning is in effect in this region.

Regular season
Thursday - January 11, 2018
Alpine

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Below Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Friday - January 12, 2018
Alpine

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Below Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Saturday - January 13, 2018
Alpine

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Below Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Avalanche Problem 1: Storm Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

Recent snowfall has formed touchy storm slabs at all elevations, especially in the south of the region. Weak layers exist below the new snow as well as deeper in the snowpack and small storm slab releases may 'step down' to a deeper weak layer.

Travel and Terrain Advice
  • The new snow sits on a persistent weak layer and will require more time than usual to stabilize.
  • If triggered, the storm slabs may step down to deeper layers resulting in large avalanches.

Avalanche Problem 2: Persistent Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

A weak layer buried 40-70 cm deep is becoming increasingly reactive in many areas of the BC interior. This layer has produced numerous large avalanches and is an increasing concern in the Cariboos - especially in the south of the region.

Travel and Terrain Advice
  • Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.
  • Numerous large avalanches have run on this layer in well supported, treed terrain.

Avalanche Summary

Reports from the past couple of days include several Size 1-1.5 persistent slab releases that were triggered remotely (from a distance). With slab depths of 30-100 cm, both the January 5 and December 15 surface hoar layers were noted as failure planes. 'Step down' type releases were also observed. These reports all came from the south of the region.

Considerably more avalanche activity has been reported from the adjacent North Columbias, where numerous persistent slabs and storm slabs have recently been observed running naturally and with remote triggers. Sizes have ranged from small to very large (Size 1-3) with slab depths from 30-100 cm. This activity has been observed on all aspects and elevation ranges, although the deeper releases running on the December 15 surface hoar have been focused at treeline and below.

Conditions in the south of the Cariboo region are quite similar to those the North Columbias at the moment, so it is advised to consider activity in this neighbouring region as indicative of the potential that exists in the Cariboos.

Please share your observations through the Mountain Information Network.

Snowpack Summary

Recent storms brought 20-50 cm of new snow to the region. The new snow sits on surface hoar on sheltered slopes as well as sun crust on steep solar aspects and the deepest accumulations exist in the south of the region. Moderate southwesterly winds accompanied this snowfall in the alpine, which created wind slabs in lee features.

As the new snow continues to consolidate, it gradually forms a dangerous slab above several persistent weak layers that exist in the snowpack. The first of these is the surface hoar that exists at the new snow interface. Recent snowpack tests and avalanche activity show a high degree of reactivity at this layer. Below it, the December 15 surface hoar is now buried 50 to 80 cm deep. Reactivity at this layer has been increasing and is most apparent at treeline and below treeline. Both of these layers are buried deeper and present greater danger in the south of the region.

Deeper in the snowpack at depths of about 70 to 100 cm, a rain crust from November is producing variable snowpack test results, from sudden fracture characters to no result. This layer is considered dormant but could be triggered in thin spots around variable snowpack areas in the alpine.

Weather Forecast

Friday: A mix of sun and cloud. Scattered flurries and up to 5 cm of new snow overnight. Light south winds. Alpine high temperatures of -6.

Saturday: Mainly cloudy with isolated flurries and a possible trace of new snow. Moderate southwest winds. Freezing level rising to 1300 metres with alpine high temperatures to -2. Cooler at lower elevations due to a temperature inversion.

Sunday: A mix of sun and cloud. Moderate to strong south winds. Freezing level to 1700 metres with alpine high temperatures increasing to +3. Cooler temperatures at lower elevations due to temperature inversion.

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

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