Avalanche Forecast

Kootenay Boundary

Date issued

Feb 15, 2018 - 3:39 PM

Valid until

Feb 16, 2018 - 2:00 PM

Prepared by

shorton

Two incoming storms will elevate the danger. Continue to choose conservative terrain and limit your exposure during the storms.

Regular season
Thursday - February 15, 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 - 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

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.

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

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.

Avalanche Problem 1: Wind Slabs

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

Wind slabs will continue to grow on Friday with strong west wind and 5-15 cm of new snow. Beware of an interface buried up to 30 cm below the surface that could support wide propagations.

Travel and Terrain Advice
  • Choose well supported terrain without convexities.
  • Use caution in lee areas in the alpine and treeline. Storm snow will form slabs.
  • Use ridges or ribs to avoid pockets of wind loaded snow.

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 steep convexities or areas with a thin or variable snowpack.
  • Minimize exposure during periods of heavy loading from new snow and wind.
  • Pay attention to overhead hazards like cornices which could trigger persistent slabs.

Avalanche Summary

Wednesday's storm produced a few small (size 1) skier-triggered slabs on north facing terrain at treeline elevations, while explosive control produced a few size 2 avalanches in wind-affected terrain.

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. These were large avalanches with fracture depths of over a metre. Natural activity on deeply buried weak layers has wound down recently, but human triggering remains a real concern.

Expect the incoming snow to form reactive slabs as well as potentially stress deeper weak layers.

Snowpack Summary

Fresh slabs will grow with the incoming storms. A few interfaces buried 20-30 cm below the most recent snow could potentially support wide propagations in the fresh storm/wind slabs. This includes sun crusts on steep south-facing slopes, a rain crust below 1800 m, small surface hoar in isolated areas, and hard wind slabs at upper elevations. Fragile cornices may be found at ridgetop.

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 persistent weak layers that lurk within the snowpack have produced large and destructive avalanches. Although this activity has been diminishing gradually, recent activity and continued sudden snowpack test results have kept them a top concern in the region.

The complex and widespread nature of our multiple overlapping persistent slab problems continues to demand respect and diligence from backcountry travelers in the region.

Weather Forecast

FRIDAY: Flurries throughout the day with 5-15 cm of new snow and then clearing in the evening, moderate to strong west wind, alpine high temperatures around -6 C.

SATURDAY: Another storm pulse brings 20-30 cm of new snow throughout the day, moderate southwest wind, alpine high temperatures around -4 C.

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