Avalanche Forecast

Sea To Sky

Date issued

Apr 10, 2018 - 4:33 PM

Valid until

Apr 11, 2018 - 2:00 PM

Prepared by

swerner

New snow and forecast strong southwest winds will continue to build reactive storm slabs. Moist and wet surface snow will weaken with warmer temperatures and rain at lower elevations.

Regular season
Tuesday - April 10, 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.

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

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.

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?

Storm slabs and loose wet avalanches may be reactive with warm and rainy weather. New storm slabs will form once the rain switches to snow. Slabs will be thicker in lee features, as the snow will fall with strong southwest winds.

Travel and Terrain Advice
  • Use ridges or ribs to avoid pockets of wind-loaded snow.
  • Avoid steep slopes when air temperatures are warm, it is raining, or the solar radiation is strong.
  • Use caution, especially in lee areas in the alpine and treeline. Storm snow is forming touchy slabs.

Avalanche Problem 2: Persistent Slabs

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

A weak layer buried 60 to 90 cm is still surprising people and producing large and destructive avalanches. Be particularly cautious around upper treeline and alpine terrain on shady aspects, where this layer is most likely to be a problem.

Travel and Terrain Advice
  • Pay attention to overhead hazards like cornices, which could trigger persistent slabs.
  • Be aware of the potential for wide propagation due to the presence of buried weak layers.
  • Avoid steep terrain or areas with a thin or variable snowpack.

Avalanche Summary

Several, natural storm slabs up to size 2 and loose wet avalanche activity from steep solar aspects were observed on Monday. Cornice control also produced size 2's but not pulling slabs from the slopes below.
Avalanche activity will be on the rise with the incoming storm. Its still winter out there!

Snowpack Summary

Warm temperatures and rain have moistened the snow surface on all aspects and at all elevations with new snow accumulations in the alpine up to 15 cm on Tuesday. Reactive storm slabs and wind slabs are building with continued snow and strong southwest winds. Ridgelines are heavily corniced and could act as a trigger on the slope below.
A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 120 cm. This layer is spotty in its distribution but has recently produced large avalanches. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.Below this, the snowpack is well-settled and strong.

Weather Forecast

Up to 10 cm expected overnight on Tuesday. New snow 5-10 cm on Wednesday. Ridgetop wind strong from the southwest and freezing levels rising to 1500 m.

Thursday: Mix of sun and cloud. New snow up to 5 cm. Ridgetop wind strong from the southwest and freezing levels 1300 m.

Friday: Yet another blast of winter up high! Heavy snow, 30-40 cm expected. Ridgetop winds strong-extreme from the southwest with freezing levels near 1400 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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