Avalanche Forecast

Kootenay Boundary

Date issued

Feb 1, 2018 - 5:00 PM

Valid until

Feb 2, 2018 - 2:00 PM

Prepared by

jlammers

Deeply buried weak layers exist throughout the region and a cautious approach remains critical. Don't let the lure of powder pull you into bigger terrain.

Regular season
Thursday - February 1, 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.

Friday - February 2, 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.

Saturday - February 3, 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

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: Persistent Slabs

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

The snowpack is complex and continues to produce very large avalanches on several weak layers buried 80 to 150 cm below the surface. Moderate-angled, simple terrain selection remains critical to safe mountain travel.

Travel and Terrain Advice
  • Good day to make conservative terrain choices.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Minimize overhead exposure; avalanches may reach the end of run out zones.

Avalanche Problem 2: Wind Slabs

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

New snow and wind on Thursday night and Friday are expected to form new wind slabs in higher elevation lee terrain. A surface avalanche in motion could be what it takes to trigger a deeper and more destructive persistent slab avalanche.

Travel and Terrain Advice
  • Avoid lee and cross-loaded terrain near ridge crests.
  • Be cautious as you transition into wind affected terrain.
  • If triggered, wind slabs may step down to deeper layers and result in large avalanches.

Avalanche Summary

Reports from Tuesday reflect increased visibility over terrain that was obscured during Monday's storm. Evidence of a natural avalanche cycle involving each of our persistent weak layers was observed, with numerous avalanches reaching Size 3.5 and several crown fractures up to 3 metres deep. These are believed to be some of the deepest crowns in the region's historical record. Here's a great MIN post from Kootenay Pass that details some of the recent activity.

On Wednesday, explosives avalanche control in the mountains near Nelson triggered a handful persistent slab avalanches in the size 3-4 range at treeline and in the alpine.

Looking forward, expect newly formed wind slabs and the persistent slabs beneath them to remain reactive to human triggers with the potential for very large and destructive avalanches.

Snowpack Summary

During the last few weeks of January, storms brought around 100 cm of snow to the region. On Monday precipitation fell as rain below about 1300 metres and a near-surface crust may exist in some areas below treeline. Where more recent precipitation fell as snow, southwest winds may have formed touchy wind slabs in high elevation lee terrain.

The critical instabilities, however, are buried well below the surface. A mixture of weak surface hoar and/or a crust from mid-January is buried beneath all the storm snow at 80-110cm deep. Numerous recent avalanches to size 2.5 have been reported on this layer and large, destructive avalanches at this interface remain a concern.

Below this layer lies a second crust/surface hoar interface buried early-January that is now 110-130 cm deep. Several recent avalanches have stepped down to this layer.

The mid-December surface hoar layer is buried 120-150 cm below the surface. This layer has continued to produce step down releases and "sudden" test results. It is most pronounced at treeline, but is also present below treeline .

Weather Forecast

Friday: 10-15cm of new snow / Moderate westerly winds / Freezing level at 1400m

Saturday: Light flurries / Moderate northwest winds / Freezing level at 1500m

Sunday: 5-10cm of new snow / Light southwest winds / Freezing level at 1700m

Note: Confidence is low for forecast wind values and precipitation amounts for Saturday and Sunday.

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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