Avalanche Forecast

Sea To Sky

Date issued

Jan 26, 2018 - 4:45 PM

Valid until

Jan 27, 2018 - 2:00 PM

Prepared by

jsmith

New snow amounts within this region will be highly variable on Saturday with more snow in the south. Hazard may be one step lower in areas that receive less than 25 cm of new snow.

Regular season
Friday - January 26, 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.

Saturday - January 27, 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

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.

Below Treeline

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.

Sunday - January 28, 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

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.

Below Treeline

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.

Avalanche Problem 1: Storm Slabs

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

New snow, strong winds, and rising temperatures will create touchy storm slabs reactive to human triggers.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Be aware of the potential for wide propagations due to the presence of hard windslabs.
  • The new snow will take time to settle and stabilize.

Avalanche Problem 2: Cornices

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

Large amounts of recent new snow and high winds are creating rapid cornice growth.

Travel and Terrain Advice
  • Falling cornices may trigger large avalanches on the slopes below.
  • Give cornices a wide berth when travelling on or below ridges.

Avalanche Problem 3: Deep Persistent Slabs

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

Large triggers such as a falling cornice or smaller storm slab avalanches may step-down to deeply buried crusts, resulting in large and destructive avalanches running full path.

Travel and Terrain Advice
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.

Avalanche Summary

Throughout this region there has been evidence of a natural avalanche cycle up to size 3 that occurred within the storm snow on Wednesday. More notable are the numerous explosive triggered, very large avalanches up to size 3.5 that where reported near Whistler on Thursday. These avalanches started in the storm snow and then stepped down to the early January and even the mid-December crusts which resulted in very large avalanches running full path. They occurred on northwesterly aspects below rocky ridgetops at around 1950 m. Although these layers are over 200 cm beneath the snow surface, a large trigger such as a falling cornice or a smaller human triggered avalanche could very likely "step-down" to these layers resulting in large and destructive avalanches.

Snowpack Summary

15-20 cm of new snow on Thursday morning brings recent storm totals to around 60-80 cm which continues to be redistributed by strong southeasterly winds. Last weekend's storm created dense storm slabs lurking in lee and cross-loaded features. Impressive cornice growth has also been observed on the lee side of ridgetops.

200-250 cm below the surface you'll find a crust that was buried early January and is present at all elevations. Below this there is another crust which was buried in mid-December. Recent explosive control work has triggered storm slab avalanches that have then "stepped-down" to both of these crusts, resulting in very large avalanches running full path. Although these layers are over 200 cm beneath the snow surface, a large trigger such as a falling cornice or a smaller human triggered avalanche could very likely "step-down" to these layers resulting in very large and destructive avalanches.

Weather Forecast

SATURDAY: 20-30 cm of new snow / Strong southwesterly ridgetop winds / Freezing level rising to around 1000m.

SUNDAY: 20-30 cm of new snow / Strong southwesterly ridgetop winds / Freezing level rapidly rising to around 1800m.

SUNDAY NIGHT: 15-25 cm of new snow / Strong southwesterly ridgetop winds / Freezing level around 1800m.

MONDAY: 25-30 cm of new snow / Strong to extreme southwesterly ridgetop winds / Freezing level around 1800m.

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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