Avalanche Forecast

Kootenay Boundary

Date issued

Jan 11, 2018 - 4:39 PM

Valid until

Jan 12, 2018 - 2:00 PM

Prepared by

jlammers

A Special Public Avalanche Warning is in effect as large, destructive avalanches continue to fail throughout the region.

Don't over-think the current avalanche scenario. Stick to extremely low angle terrain and avoid any overhead hazards.

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?

40 to 60 cm of recent storm snow has settled into a reactive slab that rests on the early January weak layer. Large natural and human triggered storm slab avalanches remain likely, and may "step-down" to deeper, more destructive layers.

Travel and Terrain Advice
  • The new snow will require several days to settle and stabilize.
  • Storm slabs in motion will likely step down and produce large destructive avalanches.
  • Avoid all avalanche terrain.

Avalanche Problem 2: Persistent Slabs

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

Our complex snowpack is currently producing very large avalanches on deeply buried weak layers. Expert level knowledge and significant experience is required to venture into the backcountry at this time.

Travel and Terrain Advice
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time

Avalanche Summary

On Tuesday a widespread natural avalanche cycle to size 2.5 was reported from all aspects and elevations as the upper snowpack adjusted to a new load and increasingly warm temperatures.

On Wednesday control work around Kootenay Pass produced very large avalanches to size 3.5 on southwest, south and southeast aspects. Natural avalanches ran to size 2.5 on southeast, east and northeast aspects. These avalanches may have started as storm slabs, but quickly stepped down to the mid-December and/or late November weak layers. An awesome MIN post from the same day also details some spooky skier-triggered avalanche activity around treeline in the Nelson area. Click here for details. At the time of publishing this bulletin, no new avalanche activity had been reported, but I don't expect conditions to have improved to any significant extent.

Looking forward, natural avalanche activity may taper-off somewhat; however, human triggering of large, destructive persistent slab avalanches at all elevation bands is expected to continue for the foreseeable future in many parts of the region.

Snowpack Summary

40 to 80 cm of recent snow is settling into a cohesive slab on top of the reactive January 5th interface which consists of a crust/surface hoar combination on steep southerly aspects and pure surface hoar on remaining aspects. The late December surface hoar also remains reactive and is now down 50 to 95 cm below the surface.

Adding to the complexity of the mid to upper snowpack is the mid-December surface hoar which is now 60 to 130 cm below the surface. This spooky interface continues to produce sudden snowpack test results and is most pronounced at treeline, but is also present below treeline. The overlying slab is now deep, dense and destructive.

Two laminated crusts created by rain events in late November lay just below the mid-December interface, and may co-exist with facets. In shallow, rocky terrain the mid-December surface hoar and the late November crust seem to be reacting together which is a volatile combination.

Weather Forecast

Friday: 3-7cm of the new snow / Light to moderate westerly winds / Freezing level at 700m

Saturday: Mix of sun and cloud / Light westerly winds / Freezing level at 800m

Sunday: Mostly clear skies / Light southwest winds / Inversion with valley temperatures hovering around freezing and alpine temperatures reaching 2600m

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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