Date issued

Apr 4, 2018 - 4:01 PM

Valid until

Apr 5, 2018 - 4:00 PM

Prepared by

jonas hoke

Good skiing can be found in sheltered terrain.

Persistent weak layers continue to show isolated signs of reactivity, this problem will likely persist for some time.

Regular season
Wednesday - April 4, 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.

Thursday - April 5, 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.

Friday - April 6, 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: Persistent Slabs

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

Persistent slabs sit on facets on polar aspects (more reactive recently), and a hard melt-freeze crust on solar aspects. Use a cautious approach in open terrain and assess the bond at these interfaces carefully before committing to a slope.

Travel and Terrain Advice
  • Avoid shallow snowpack areas where triggering is more likely.
  • Watch for signs of instability such as whumpfing, or cracking.

Avalanche Problem 2: Wind Slabs

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

In most cases this interface presents as a manageable surface instability and is expected to go dormant pretty quickly.

Travel and Terrain Advice
  • Use caution on open slopes and convex rolls
  • If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Avalanche Problem 3: Cornices

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

Cornices continue to grow with fresh snow and wind. Several failures were noted in the past week, in most cases triggering a slab below.

Travel and Terrain Advice
  • Give cornices a wide berth when travelling on or below ridges.
  • Minimize exposure during periods of loading from new snow and wind.

Avalanche Summary

On Tuesday, avalanche control at Marmot Basin using explosives produced several size 2 slab avalanches. These were on Northerly alpine slopes, and failed on persistent weak layers. A recent MIN report from the Bald Hills has a good photo of an avalanche that occurred on an alpine NE aspect (from the photo it looks to have been skier triggered).

Snowpack Summary

Recent storm snow has been blown in to a wind slab up to 30cm thick. This has added to the previous slab sitting on a sun-crust on solar aspects and facets on polar aspects - these are now buried as deep as 60cm. Underneath the variable slab in the upper snowpack, as well as in shallow areas, the snowpack is generally facetted and weak.

Weather Forecast

A westerly flow in the upper atmosphere is pushing a series of weak frontal systems over our area, giving cool temps and light flurries.

Up to 5 cm of snow will fall overnight into Thursday, with moderate SW ridgetop winds (tapering to light mid-morming). Alpine temps will be cold, with an overnight low of -18C, and a daytime high of -10C.

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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