Avalanche Forecast

Northwest Coastal

Date issued

Apr 3, 2018 - 5:14 PM

Valid until

Apr 4, 2018 - 2:00 PM

Prepared by

simonhorton

Fresh storm slabs will be reactive to human triggers at higher elevations. Use extra caution on south-facing slopes when the sun is out.

Regular season
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.

Wednesday - April 4, 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.

Thursday - April 5, 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.

Avalanche Problem 1: Storm Slabs

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

15-30 cm of new snow with moderate west wind has formed fresh slabs. Human triggering is likely in steep terrain and where the wind has formed thicker deposits.

Travel and Terrain Advice
  • If triggered, storm slabs may step down to deeper layers, resulting in large avalanches.
  • Use caution on open slopes and convex rolls
  • Minimize exposure to steep sun exposed slopes when the solar radiation is strong.

Avalanche Problem 2: Persistent Slabs

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

A buried surface hoar layer produced large slab avalanches at the end of March. There's some uncertainty as to how long this layer will remain a problem, but it's best to carefully evaluate sheltered north and east slopes.

Travel and Terrain Advice
  • Use extra caution in open trees and sheltered features where surface hoar may be preserved.
  • Pay attention to overhead hazards like cornices which could trigger persistent slabs.

Avalanche Summary

Preliminary reports from Tuesday suggest some avalanche activity likely occurred at higher elevations during the storm.

No new avalanches were reported on Monday and activity on Sunday was limited to a few small loose avalanches on steep sun-exposed slopes.

Last week, large persistent slab avalanches were reported on east to northeast aspects at all elevations. These were failing on the early-March and mid-March layers.

Snowpack Summary

10-30 cm of new snow sits above a variety of crusts on all but high north aspects.

In the south of the region, 70 to 90 cm of snow overlies two layers of surface hoar. The layers are most prominent on north to east aspects and were buried early-March and mid-March. In the north of the region, these layers are around 40 cm deep.

Shallower parts of the region, such as the far north, have weak sugary facets near the bottom of the snowpack.

Weather Forecast

WEDNESDAY: Mostly sunny, light wind, freezing level up to 600 m, alpine high temperatures near -8 C.

THURSDAY: Snow starting in the morning with 4-8 cm accumulations by the afternoon, strong south wind, freezing level near valley bottom, alpine high temperatures near -10 C.

FRIDAY: Continued light flurries with another 5 cm of snow, moderate south wind, freezing level up to 600 m, alpine high temperatures near -8 C.

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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