Avalanche Forecast

Sea To Sky

Date issued

Dec 5, 2017 - 4:55 PM

Valid until

Dec 6, 2017 - 2:00 PM

Prepared by

mgrist

Don't let your guard down with the sunny weather and fresh snow. Take a cautious approach towards more aggressive terrain - especially steep, wind-affected terrain.

Regular season
Tuesday - December 5, 2017
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

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 - December 6, 2017
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

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 - December 7, 2017
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

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.

Avalanche Problem 1: Loose Wet

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

Conditions will be more like spring than winter this week. Surface snow layers can become weak when hit by the sun. Minimize your exposure to terrain traps - even small sluffs can push you into dangerous terrain.

Travel and Terrain Advice
  • Use extra caution on sunny slopes or if the snow is moist or wet.
  • Use caution above cliffs and terrain traps, where small avalanches may have severe consequences.

Avalanche Problem 2: Wind Slabs

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

Wind slabs have been building over a crust layer in specific, mostly north facing locations. This layer may slide easily, particularly on steep convex terrain or where the wind has blown it into more cohesive slabs.

Travel and Terrain Advice
  • Be alert to changing snow conditions, especially where the snow firms up or sounds hollow.
  • Avoid steep lee and cross-loaded features
  • Use ridges or ribs to avoid pockets of wind loaded snow.

Avalanche Summary

On Sunday, a Size 1 storm slab was reported in the north of the region - on a steep, unsupported convex roll.

Otherwise, no new avalanches observed.

Snowpack Summary

Approximately 40-60 cm of snow from late last week now sits on top of a rain crust (or multiple crusts) that formed during the wet weather at the end of November. The snow appears to be bonding well to the crust with no avalanche activity reported recently on this layer.

Up high, the main concern has been winds (first from the south, and more recently from the north) that have blown snow around in exposed areas creating drifts and scoured areas. The take-home message is that wind slabs can be found on many aspects at higher elevations - including some southerly aspects, which is an unusual pattern.

Other than steep south facing slopes, much of the riding in the region consists of 20-30cm of low density snow that is right-side up (the snow gets more dense as you go deeper into the snowpack).

Weather Forecast

We're into a period of fine weather for the foreseeable future, with significant warming from Wednesday onwards.

Wednesday: Sunny. Light northerly winds. Freezing levels 3000m. Alpine high temperatures to +2 Celsius.

Thursday: Sunny and warm. Freezing levels around 3500 m. Light northwesterly winds. Alpine high temperatures to +5 Celsius.

Friday: Sunny and warm. Freezing levels around 3400 m. Light northerly winds.

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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