Date issued

Feb 20, 2018 - 4:00 PM

Valid until

Feb 21, 2018 - 4:00 PM

Prepared by

deryl kelly

A stiff, persistent slab sitting over weak layers will continue to plague the back-country for the foreseeable future. The greatest concern is at, and just above, treeline however these slabs are represented at all elevations and on all aspects.

Regular season
Wednesday - February 21, 2018
Alpine

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.

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.

Thursday - February 22, 2018
Alpine

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.

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.

Friday - February 23, 2018
Alpine

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.

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: Persistent Slabs

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

A stiff slab 50 to 90cm thick, sits over sun crusts on south and west aspects, Surface Hoar preserved at, and just above treeline and weak faceted crystals lurking in shallow snowpack features. This is a dangerous problem that is difficult to avoid.

Travel and Terrain Advice
  • Watch for whumpfing, hollow sounds, and shooting cracks.
  • Use conservative route selection, stick to supported terrain features, avoid overhead hazards.

Avalanche Problem 2: Wind Slabs

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

While the winds have abated, they blew hard, and from a variety of directions last week. Windslabs are hard in the alpine and they exist well into treeline areas. These can be expected to be be sensitive to skier triggering.

Travel and Terrain Advice
  • The best powder will be found in sheltered locations at or below treeline.
  • If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Avalanche Summary

No new avalanche activity observed or reported in the last week however an extensive cycle resulted when the persistent slab became overloaded with successive storms totalling 50cm each on January 30th and February 8th. Avalanches to size 3.5 were observed from most aspects and at most elevations with the majority of the action seen around 21-2500m

Snowpack Summary

15cm snow over the last week, and available snow from the previous storms, has been redistributed by strong winds from variable directions to build slabs and wind effect in open areas. A persistent slab sitting on three weak layers down 50 to 80cm can be found throughout the forecast region and has produced many large avalanches traveling full path

Weather Forecast

Cold arctic air dominating the region. Alpine high forecasted to be -22 for Wednesday with broken skies and light north winds. Brrr!

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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