Avalanche Forecast

Northwest Coastal

Date issued

Apr 11, 2018 - 5:02 PM

Valid until

Apr 12, 2018 - 2:00 PM

Prepared by

jsmith

Forecast new snow and wind Wednesday night are expected to create fresh storm slabs reactive to human triggers.

Regular season
Wednesday - April 11, 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.

Thursday - April 12, 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.

Friday - April 13, 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: Storm Slabs

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

New snow may bond poorly to an underlying crust. Watch for fresh storm slabs in leeward areas near ridge crests and convex features, as well as loose snow releases in steep terrain.

Travel and Terrain Advice
  • Use caution in lee areas in the alpine and treeline. Storm snow may form touchy slabs.
  • Use small slopes with low or no consequence to test the bond of the new snow.
  • Watch for signs of instability such as whumphing, cracking, or recent natural avalanching.

Avalanche Problem 2: Loose Wet

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

Sun and daytime warming are factors to keep in mind. Watch for wet snow on sunny aspects and lower elevation slopes, especially in the afternoon.

Travel and Terrain Advice
  • Watch for signs that the snow is heating up such as pin-wheeling or the surface snow becoming moist.
  • Avoid steep terrain that is in the sunshine.

Avalanche Summary

Numerous natural loose wet avalanches on all aspects up to size 2 and several natural wind slabs on north aspects up to size 2.5 were reported near Bear Pass on Tuesday. Forecast snow and wind on Wednesday night are expected to create fresh storm slabs reactive to human triggers.

Snowpack Summary

Rain and warming to ridge top elevations have created wet or moist snow in the top 20-30 cm of the snowpack that is likely to be covered by 5-15 cm of new snow by Thursday morning. The new snow and strong southeasterly winds are expected to form fresh storm slabs reactive to human triggers. In the south of the region, two layers of surface hoar are buried approximately 70-100 cm deep. 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.

Bellow these March layers the mid-pack is generally well-settled and strong. However, shallower parts of the region, such as the far north, have weak sugary facets near the bottom of the snowpack.

Weather Forecast

TONIGHT: 5-15 cm new snow. Strong southeasterly ridgetop winds. Freezing level around 500 m.

THURSDAY: Cloudy with flurries. Light southwesterly ridgetop winds. Freezing level around 1000 m.

FRIDAY: 5-15 cm new snow. Strong southwesterly ridgetop winds. Freezing level around 1000 m.

SATURDAY: 5-10 cm new snow. Moderate southwesterly ridgetop winds. Freezing level around 1000 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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