Date issued

Apr 19, 2018 - 6:55 PM

Valid until

Apr 20, 2018 - 4:00 PM

Prepared by

Rupert Wedgwood

Avoid all slope with cornices overhead as there is plenty of evidence of them falling recently with significant consequences.

Regular season
Friday - April 20, 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

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.

Saturday - April 21, 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

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.

Sunday - April 22, 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

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.

Avalanche Problem 1: Wind Slabs

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

Although mostly thin some wind slabs are up to 40cm thick in alpine terrain. Solar radiation and cornice collapses can trigger these events. Once triggered the potential to trigger deeper weaknesses exists resulting in larger avalanches.

Travel and Terrain Advice
  • Use caution on open slopes and convex rolls
  • Use caution in lee areas. Recent wind loading has created wind slabs.

Avalanche Problem 2: Loose Wet

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

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

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

Avalanche Problem 3: Persistent Slabs

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

These events require a significant force to trigger them such as a large cornice failure or avalanche debris from above. Once triggered they can be very large and run far into the valley below. Many slopes have already been triggered.

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 Summary

In the past 36hrs persistent slab avalanches up to size 3.5 have occurred from alpine terrain. Most are in the 2 to 2.5 range and are are being triggered by cornice failures or small windslab avalanches stepping down to these deeper layers. With freezing levels reaching treeline expect some loose avalanches on South to West facing slopes.

Snowpack Summary

Below 1,900m the snowpack is isothermal. 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 cornices. Soft windslabs have been developing and are up to 40cm deep.

Weather Forecast

Cooler temperatures Friday with freezing levels at 1,900m close to Jasper and 2,300m at the Icefields, where it will be mainly cloudy with isolated flurries. Alp High -2 C low -6C Ridge wind SW 15 km/h gusting to 40 km/h. Limited Solar at the Icefields, but more near Jasper. On Saturday up to 10cm of fresh snow is forecast.

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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