Avalanche Forecast

Kootenay Boundary

Date issued

Feb 16, 2018 - 4:08 PM

Valid until

Feb 17, 2018 - 2:00 PM

Prepared by

shorton

Intense snowfall will elevate the danger. Travel in avalanche terrain is not recommended on Saturday.

Regular season
Friday - February 16, 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 - February 17, 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.

Sunday - February 18, 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.

Avalanche Problem 1: Storm Slabs

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

Storm slabs will become very reactive with another 20-40 cm of snow expected on Saturday. Natural and human-triggered avalanches are very likely.

Travel and Terrain Advice
  • Avoid avalanche terrain during periods of heavy loading from new snow and wind.

Avalanche Problem 2: Persistent Slabs

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

Several deeply buried weak layers exist in the snowpack. Although the likelihood of triggering a persistent slab is gradually decreasing, the consequences remain very high.

Travel and Terrain Advice
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Pay attention to overhead hazards like cornices.

Avalanche Summary

A few small slabs were reactive to skier and explosive triggers as storm snow accumulated on Wednesday-Friday. They were primarily small (size 1) and in wind-affected terrain at treeline and alpine elevations.

Last weekend, three large persistent slab avalanches (size 3) were reported on northeast aspects in the Valhallas. Two were triggered with explosive and the third was naturally triggered.

By Saturday, storm slabs will be much larger and more reactive while deeper weak layers may be getting stressed by the weight of the new snow.

Snowpack Summary

Storm snow has been accumulating for a few days. Saturday's storm is expected to deliver 20-40 cm on top of the 20-30 cm from the past few days. All this new snow is sitting above an interface that could favour wide propagations in the storm snow. The interfaces include sun crusts on steep south-facing slopes, a rain crust below 1800 m and small surface hoar in isolated areas.

We now have 1-2 m of settled snow sitting on three significant surface hoar/crust layers that were formed early to mid-January, and back in December. Near the base of the snowpack a crust/facet interface exists that will likely haunt us all season. These layers produced large destructive avalanches on a regular basis up until last weekend. Avalanche activity on these layers has gradually diminished, but the persistent slab problem still demands respect and diligence.

Weather Forecast

SATURDAY: Heavy snow with 20-40 cm by the end of the day, moderate west wind, alpine high temperatures around -8 C.

SUNDAY: Lingering flurries with light east wind and alpine high temperatures around -15 C.

MONDAY: Mix of sun and cloud with light northeast wind and alpine high temperatures around -17 C.

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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