Avalanche Forecast

Sea To Sky

Date issued

Apr 6, 2018 - 4:24 PM

Valid until

Apr 7, 2018 - 2:00 PM

Prepared by

mconlan

Snow is forecasted for Saturday with associated strong winds. Be cautious of periods of rapid precipitation or wind loading, as avalanche activity may increase.

Regular season
Friday - April 6, 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

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.

Saturday - April 7, 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

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.

Sunday - April 8, 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?

Recent snowfall has formed new slabs. More snow is forecasted for Saturday, which will build thicker slabs. Observe for the bond of new snow with the old surface before committing into avalanche terrain.

Travel and Terrain Advice
  • Minimize exposure during periods of heavy loading from new snow, wind or rain.
  • Use ridges or ribs to avoid pockets of wind-loaded snow.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.

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 Problem 3: Cornices

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

Cornices are very large and fragile. Give them a large berth if travelling on ridges and avoid travelling underneath them, as they can trigger large avalanches.

Travel and Terrain Advice
  • Give cornices a wide berth when travelling on ridges.
  • Avoid travelling on slopes below cornices.

Avalanche Summary

On Thursday, small loose dry, loose wet, and storm slab avalanches were reactive to skier triggers.

On Wednesday, skiers triggered a large persistent slab in alpine terrain. It was reported as a size 3, 50-200 cm deep.

Snowpack Summary

New snow and strong southerly winds are creating new slabs at higher elevations. This snow overlies various old surfaces including previous storm snow, melt freeze crusts on sunny aspects, and old wind slabs. On ridges, cornices are reported to be large and fragile. At lower elevations, precipitation is falling as rain and creating wet snow conditions.

A weak layer consisting of surface hoar, facets, or a sun crust from late March is now buried about 60 to 90 cm. This layer is spotty in its distribution but has recently produced large avalanches. It is mostly likely to be problematic on shady aspects between 1900 m and 2250 m.

Below this, the snowpack is well-settled and strong.

Weather Forecast

SATURDAY: Cloudy with snowfall, accumulation 10 to 20 cm, strong southerly winds, alpine temperature -3 C, freezing level 1600 m.

SUNDAY: Mostly cloudy with light snowfall, accumulation 2 to 5 cm, light westerly winds, alpine temperature -3 C, freezing level 1600 m.

MONDAY: Mostly cloudy, light southwesterly winds, alpine temperature -3 C, freezing level 1600 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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