Date issued

Nov 19, 2017 - 4:00 PM

Valid until

Nov 20, 2017 - 4:00 PM

Prepared by

conrad janzen

Continued snowfall with strong winds overnight will increase the danger at all elevations Monday. Plenty of reports of avalanche activity and a couple close calls over the last two days mean this is a good time to stay out of avalanche terrain.

Regular season
Monday - November 20, 2017
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

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.

Tuesday - November 21, 2017
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

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.

Wednesday - November 22, 2017
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

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.

Avalanche Problem 1: Wind Slabs

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

Strong SW winds are moving a great deal of snow into lee areas at treeline and above, with lots of sluffing in steep terrain. Wind slabs have formed near ridge crests with slabs extending further down slope that are easy to trigger.

Travel and Terrain Advice
  • Minimize overhead exposure during periods of heavy loading from new snow, wind.
  • If triggered the wind slabs may step down to deeper layers resulting in larger avalanches.

Avalanche Problem 2: Persistent Slabs

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

The snow that fell on the Halloween crust became faceted by the early November cold snap. Soft slabs of snow now sit above this weak snow and are becoming increasingly reactive to skier traffic and small triggers such as sluffs out of steep terrain.

Travel and Terrain Advice
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.
  • Minimize exposure to steep, planar slopes.

Avalanche Summary

Continued reports of natural and skier triggered avalanche activity on Sunday. Local ski hills reported easily triggered wind slabs and persistent slabs up to size 2 with ski cutting and explosives. Several reports of natural avalanches in back country areas around Bow Summit and Emerald Lake, and one avalanche incident on Mt Crowfoot.

Snowpack Summary

Strong SW winds with 5-15cm of new snow in the last 24 hours are creating slabs in lee areas at treeline and above which are reactive to skiers. The snowpack at treeline is from 60-90 cm deep across the region. The main feature in the snowpack is a buried layer of facets now down 30 to 50 cm and sitting on the Halloween crust in areas below 2700m.

Weather Forecast

Strong SW winds accompanied by moderate snowfall amounts should continue through Sunday night with snowfall amounts of 10-15 cm. Temperatures will remain in the -5 to -10'C range. The winds and snowfall start easing Monday morning with temperatures cooling, then remaining steady until a slight rise on Wednesday.

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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