Avalanche Forecast

Northwest Coastal

Date issued

Mar 31, 2018 - 4:27 PM

Valid until

Apr 1, 2018 - 2:00 PM

Prepared by

mconlan

Storm slabs exist in the south of the region from recent snowfall. This overlies a couple touchy weak layers. Be cautious on southerly aspects when the sun is out. Conservative decision-making is recommended.

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

Avalanche Problem 2: Storm Slabs

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

Recent snowfall of up to 40 cm in the south of the region have formed reactive storm slabs.  Slabs may be more reactive on sunny and lee slopes. Observe for signs of instability within the snow, such as cracking, whumpfing, and avalanche activity.

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

Avalanche Summary

On Friday, a natural cycle within the recent storm snow occurred, failing as storm slabs and loose dry avalanches. They were small to large (size 1 to 2), on all aspects, and at all elevations. See this MIN report to observe some of the avalanches.

Previously in the week, large persistent slab avalanches were reported at all elevation bands, on east to northeast aspects. These were failing on the early- and mid-March layers described in the Snowpack Discussion.

Snowpack Summary

Thursday’s storm dumped 30 to 40 cm of snow in the south of the region, such as around Terrace and Shames.  There is now about 70 to 90 cm of storm snow that overlies two layers of surface hoar, which were 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

SUNDAY: Early-morning snowfall then mostly sunny, accumulation 2 to 5 cm with possible localized higher amounts from convective flurries, light northeasterly winds, alpine temperature -9 C, freezing level 600 m.

MONDAY: Mostly cloudy with afternoon snowfall, accumulation 1 to 3 cm, light southerly winds, alpine temperature -9 C, freezing level 600 m.

TUESDAY: Mostly cloudy with early-morning snowfall, accumulation 5 to 10 cm, light southwesterly winds, alpine temperature -10 C, freezing level 500 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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