Avalanche Forecast

Kootenay Boundary

Date issued

Jan 24, 2018 - 4:01 PM

Valid until

Jan 25, 2018 - 2:00 PM

Prepared by

jsmith

Additional snow and wind Wednesday night will continue to create touchy storm slabs reactive to human triggers. If triggered, these slabs have the potential to step down to deeper weak layers buried in the snowpack, resulting in large avalanches.

Regular season
Thursday - January 25, 2018
Alpine

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.

Treeline

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.

Below Treeline

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.

Friday - January 26, 2018
Alpine

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.

Treeline

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.

Below Treeline

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.

Saturday - January 27, 2018
Alpine

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.

Treeline

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.

Below Treeline

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.

Avalanche Problem 1: Storm Slabs

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

Additional snow and wind Wednesday night will continue to create touchy storm slabs reactive to human triggers. If triggered, these slabs have the potential to step down to deeper weak layers buried in the snowpack.

Travel and Terrain Advice
  • Be cautious when transitioning into wind effected terrain.
  • Use small slopes with low or no consequence to test the bond of the new snow.
  • 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?

The snowpack is complex and has produced very large avalanches on up to four separate weak layers buried 50 to 140cm below the surface. A conservative approach and moderate-angled, simple terrain are good ways to manage a complex snowpack.

Travel and Terrain Advice
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Avalanche Summary

On Tuesday, a skier triggered size 2 persistent slab avalanche was reported in the Rossland area. No further information was reported but it is suspected to have failed on the surface hoar layer buried in early January which was down 75cm. The slope that slid was low angle and the slab propagated across the entire slope. Additionally, a snowcat northwest of Nelson triggered two size 2.5 persistent slab avalanches on the same early January surface hoar layer which was down around 80 cm at 2250m. Forecast new snow and wind Wednesday night will promote ongoing storm slab avalanche activity, especially in higher elevation, lee terrain.

Snowpack Summary

20-25cm of new snow brings recent storm snow total to approximately 45-60 cm which has been redistributed by strong southerly winds. This overlies the most recent crust and surface hoar (weak feathery crystals) layer that was buried mid-January. This crust can be found on solar aspects while the surface hoar has been buried on shaded aspects above 1600m. Below this layer lies a second crust/surface hoar interface buried early-January that is now 70-100 cm below the surface.

The mid-December surface hoar layer is buried 100-130 cm below the surface. This spooky layer still produces "sudden" test results and is most pronounced at treeline, but is also present below treeline .

Two laminated crusts created by rain events in late November lay just below the mid-December interface, and may co-exist with facets.

Weather Forecast

WEDNESDAY NIGHT: 10-20cm of new snow / Moderate to strong southerly ridgetop winds / Freezing level around 1000m.

THURSDAY: Mostly cloudy with isolated flurries / Light to moderate southerly ridgetop winds / Freezing level dropping to 800m.

FRIDAY: Mostly cloudy with flurries; 3-5cm / Light to moderate southwesterly ridgetop winds / Freezing level dropping to valley bottom with an alpine high of -8.

SATURDAY: 5-15 cm of new snow / Moderate southerly ridgetop winds / Alpine high of -4.

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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