Avalanche Forecast

Northwest Coastal

Date issued

Mar 30, 2018 - 4:27 PM

Valid until

Mar 31, 2018 - 2:00 PM

Prepared by

mconlan

Up to 40 cm of snow fell in the south of the region. This snow formed storm slabs and is loading buried weak layers. Be cautious on southerly aspects when the sun is out. Conservative decision-making is recommended, as large avalanches are likely.

Regular season
Saturday - March 31, 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.

Sunday - April 1, 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.

Monday - April 2, 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?

A weak surface hoar layer buried about 50 cm has produced large slab avalanches that have propagated widely. It is best to avoid sheltered north to easterly slopes, where this layer is most likely to be a problem.

Travel and Terrain Advice
  • Be aware of the potential for large, destructive avalanches due to buried surface hoar.
  • Use extra caution in open trees and sheltered features where surface hoar may be preserved.

Avalanche Problem 2: Storm Slabs

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

Up to 40 cm of snow fell in the south of the region on Thursday. Observe for signs of slab properties and instability within this snow, such as cracking, whumpfing, and avalanche activity.

Travel and Terrain Advice
  • Be aware of the potential for loose dry avalanches in steep terrain where snow hasn't formed a slab.
  • Approach lee and cross-loaded slopes with caution.
  • If triggered, storm slabs may step down to deeper layers, resulting in large avalanches.

Avalanche Summary

On Thursday, large (size 2.5 to 3) storm and wind slabs were triggered naturally and by explosives, with slab depths up to 100 cm.

On Tuesday and Wednesday, large (size 2 to 3) persistent slab avalanches and storm slab avalanches were reported in the region at alpine and treeline elevations, being remotely triggered (from a distance) as well as by explosives, 50 to 150 cm deep, and on northeasterly aspects.

Snowpack Summary

Thursday's storm dumped 30 to 40 cm of snow in the south of the region, such as around Terrace and Shames. This overlies last weekends storm snow, which was redistributed with strong westerly winds in exposed areas at higher elevations.

Two layers of surface hoar exist in the region at depths of about 60 to 80 cm, being buried early and mid-March. At low elevations, the storm snow sits on a melt-freeze crust.

Dormant weak layers exist deeper in the snowpack. Layers of crusts, facets, and isolated surface hoar from mid- and late-February are buried 100 to 150 cm. Near the bottom of the snowpack, weak and sugary facets exist in shallower parts of the region, such as the far north.

Weather Forecast

SATURDAY: Sunny with afternoon clouds, light southwesterly winds, alpine temperature -6 C, freezing level 700 m.

SUNDAY: Early-morning snowfall then partly cloudy, accumulation 5 to 10 cm, light northeasterly winds, alpine temperature -6 C, freezing level 700 m.

MONDAY: Partly cloudy with afternoon snowfall, light southerly winds, alpine temperature -6, freezing level 600 m.

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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