Date issued

Apr 21, 2018 - 4:00 PM

Valid until

Apr 22, 2018 - 4:00 PM

Prepared by

Jonas Hoke

Good skiing remains on on sheltered and shaded slopes. Recent persistent slab activity is a sign that ski mountaineering season is not here quite yet.

Regular season
Sunday - April 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

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.

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.

Monday - April 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

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.

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 - April 24, 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.

Avalanche Problem 1: Persistent Slabs

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

Avoid travel on steep slopes that have not had recent avalanche activity. These events have been most reactive to large triggers, such as a cornice failure or smaller avalanche, but may be reactive to the weight of a skier in the wrong place.

Travel and Terrain Advice
  • Avoid shallow snowpack areas where triggering is more likely.
  • Pay attention to overhead hazards like cornices which could easily trigger deep slabs.

Avalanche Problem 2: Wind Slabs

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

SW winds Saturday have added to the existing wind slab and cornice problem. Although mostly thin, some wind slabs are up to 40cm thick in alpine terrain. Once initiated the potential to trigger deeper weaknesses exists resulting in larger avalanches.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Stay well to the windward side of corniced ridges.

Avalanche Problem 3: Loose Wet

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

Pay close attention to the effect of solar radiation and daytime warming. Point release from rocks and cliff terrain can trigger isothermal snow below. This will be of most concern in the late afternoon.

Travel and Terrain Advice
  • Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.
  • Use extra caution on solar slopes or if the snow is moist or wet.

Avalanche Summary

Report of a large persistent slab avalanche (size 2.0) on the NE slopes of Lectern, initiating in the alpine and running in to treeline.

Last weeks avalanche activity is still visible in many location - a good reminder to avoid steep terrain that has not had recent avalanche activity (especially on Northerly aspects).

Snowpack Summary

Windslabs are up to 40cm deep. Sun or temperature crusts extend to treeline and continued into the alpine on southerly slopes. Persistent slabs can be found on most aspects at treeline and above. These have been most reactive recently to large triggers like cornice failures. Below 1,900m the snowpack is going isothermal on a daily basis.

Weather Forecast

A building ridge of high pressure brings a warming trend that likely marks the end of winter.

Sunday will be partly cloudy, with the freezing level rising to 1800m, an Alpine High of -4C, and light to moderate NW winds.

The warming trend begins in ernest Monday, with Clear skies forecast through the week, and the freezing level surpassing 3000m by Thursday.

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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