Avalanche Forecast

Sea To Sky

Date issued

Mar 16, 2018 - 4:56 PM

Valid until

Mar 17, 2018 - 2:00 PM

Prepared by

cgarritty

Maintain elevated caution around lingering wind slabs, looming cornices, and during the daily cycle of loose wet avalanche conditions.

Regular season
Friday - March 16, 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

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.

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 - March 17, 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

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.

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 - March 18, 2018
Alpine

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.

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.

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: Wind Slabs

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

Wind slabs still linger on north aspects at higher elevations. On sheltered slopes, slabs may overlie a more reactive layer of surface hoar. South aspects are an additional daily concern as sun and warming set up loose wet avalanche conditions.

Travel and Terrain Advice
  • Watch for wind-loaded pockets around ridgecrests and in the lee of exposed terrain features.
  • Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.
  • Give cornices a wide berth while on or below ridges. Cornice falls may trigger large avalanches.

Avalanche Summary

Reports from Thursday included two recent natural storm slab releases in the Whistler area. One was a thin size 1.5 that released on a steep slope just below a ridge crest and the other is a more concerning size 3.5 that was seen on the Cheakamus Glacier from Whistler. We don't have details on the failure plane of this second release, but it may have run on the mid-February crust that was widely active about a week ago.

Monday's reports included observations of three natural size 2.5 loose wet avalanches that released from steep, rocky, south-facing slopes in the afternoon in the Whistler area.

Snowpack Summary

A new crust exists on the surface on solar aspects at all elevations while new surface hoar has begun to form on shaded and sheltered higher elevations. Below the surface, a wind-redistributed 5-20 cm of new snow from a mid-week storm overlies a crust on all but high elevation north aspects, where it has buried dry, wind redistributed snow from last week's storms.

Last week's storms buried a weak layer composed of soft facets, surface hoar, and/or crust found roughly 50-100 cm below the surface. A week ago this layer was producing whumpfing, sudden results in snowpack tests, and even some remotely triggered avalanches. Much of this activity was attributed to buried surface hoar on north aspects at upper treeline elevations. This buried weak layer is a limited but lingering concern in a snowpack that is otherwise well settled and strong beneath this interface.

Variable winds in the past month have built up cornices on many ridgelines. They will become touchier as daily temperatures rise and when they are subject to the strong late-winter sun on clear days.

Weather Forecast

Saturday: Mainly sunny. Light east winds. Freezing level to 1500 metres with alpine high temperatures of -4.

Sunday: Cloudy with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1200 metres with alpine high temperatures of -5.

Monday: Mainly cloudy. Light west winds. Freezing level to 1300 metres with alpine high temperatures of -4.

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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