Avalanche Forecast

Kootenay Boundary

Date issued

Apr 16, 2018 - 4:29 PM

Valid until

Apr 17, 2018 - 2:00 PM

Prepared by

mconlan

More snow is expected on Tuesday. Observe for the bond of the new snow to the previous surfaces before committing into avalanche terrain. Be particularly cautious under periods of rapid snowfall loading, as avalanche activity will likely increase.

Regular season
Monday - April 16, 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

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.

Tuesday - April 17, 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

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.

Wednesday - April 18, 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

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.

Avalanche Problem 1: Storm Slabs

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

20 to 30 cm of snow fell on Monday, producing slabs that may not bond well to previous surfaces, including wet snow at low elevations, a crust at higher elevations, and wind slabs near ridge tops. More snow on Tuesday will make the slabs touchier.

Travel and Terrain Advice
  • Observe for the bond of new snow with the old surface before committing into avalanche terrain.
  • Avoid avalanche terrain under periods of rapid snowfall or wind-transport loading.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

Avalanche Problem 2: Loose Wet

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

Precipitation will fall as rain at low elevations. The snow will rapidly weaken and could slide easily with the weight of a human, producing large avalanches.

Travel and Terrain Advice
  • Avoid steep slopes when air temperatures are warm or when it is raining.
  • Use caution above cliffs and terrain traps where small avalanches may have severe consequences.

Avalanche Summary

On Sunday, many loose wet avalanches and storm slab avalanches were triggered naturally and by explosives.  They were large (size 2 to 2.5) and on all aspects between 1700 m and 2100 m. 

Snowpack Summary

Around 20 to 30 cm of snow fell on Monday.  This fell on moist snow or a melt-freeze crust up to at least 1800 m produced from rain and warm temperatures on Sunday.  Numerous other melt-freeze crusts exist in the upper snowpack from rain, sun, and warming during the spring season. The snowpack below this is generally well-settled and strong.

At lower elevations below treeline, a spring snowpack exists.

Weather Forecast

TUESDAY: Cloudy with snowfall, accumulation 10 to 20 cm, light to moderate west winds, alpine temperature -3 C, freezing level 1500 m.

WEDNESDAY: Mostly sunny and afternoon clouds, light southeast winds, alpine temperature -3 C, freezing level 1500 m.

THURSDAY: Mostly sunny, light southwest winds, alpine temperature 0 C, freezing level 2000 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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