Avalanche Forecast

Northwest Coastal

Date issued

Apr 1, 2018 - 4:13 PM

Valid until

Apr 2, 2018 - 2:00 PM

Prepared by

mconlan

Storm slabs overlie a couple weak layers, which have produced large and destructive avalanches. Observe for signs of instability within the snow before committing yourself into avalanche terrain, such as cracking, whumpfing, and avalanche activity.

Regular season
Sunday - April 1, 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.

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.

Tuesday - April 3, 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.

Avalanche Problem 1: Persistent Slabs

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

A weak surface hoar layer buried 50 to 90 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?

Although storm slab activity has decreased, it is still possible to trigger them. Slabs may be more reactive on lee slopes where the snow has more slab properties.

Travel and Terrain Advice
  • Be aware of the potential for loose 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 Saturday, a large persistent slab avalanche was reported in the north of the region, failing on the early-March weak layer described in the Snowpack Discussion.  It failed on an easterly aspect around treeline.  Otherwise, there was further evidence of the natural cycle that occurred on Friday within the recent storm snow, with storm slab and loose dry avalanches.  They were small to large (size 1 to 2), on all aspects, and at all elevations.

Last 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

Expect to find a surface crust on southerly aspects from the weekend’s clear skies.

In the south of the region, there is about 70 to 90 cm of storm snow from last week that overlies two layers of surface hoar, which are most prominent on north to easterly aspects and were buried early- and mid-March. In the north of the region, these layers are around 40 cm deep.  At low elevations, last week’s storm snow sits on a melt-freeze crust.

Near the bottom of the snowpack, weak and sugary facets exist in shallower parts of the region, such as the far north.

Weather Forecast

MONDAY: Mostly cloudy with afternoon snowfall, accumulation 1 to 3 cm, light southwesterly winds, alpine temperature -10 C, freezing level 500 m.

TUESDAY: Cloudy with snowfall, accumulation 10 to 15 cm, light southwesterly winds, alpine temperature -10 C, freezing level 500 m.

WEDNESDAY: Mostly cloudy with light snowfall, accumulation 1 to 3 cm, light southerly winds, alpine temperature -9 C, 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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