Avalanche Forecast

South Rockies

Date issued

Mar 3, 2018 - 4:42 PM

Valid until

Mar 4, 2018 - 2:00 PM

Prepared by

cgarritty

The sun packs a powerful punch this time of year. Increase your caution around slopes that see direct sunshine on Sunday.

Regular season
Saturday - March 3, 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

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.

Sunday - March 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

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.

Monday - March 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.

Avalanche Problem 1: Storm Slabs

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

Our new snow will need time to settle and bond to the surface. As it does, natural avalanching will taper off while slabs remain reactive to human triggering. Stick to supported slopes and expect direct sunshine to quickly destabilize the new snow.

Travel and Terrain Advice
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability such as recent avalanches or shooting cracks.
  • Avoid exposure to steep, sun exposed slopes when the solar radiation is strong.

Avalanche Problem 2: Deep Persistent Slabs

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

Deeply buried weak layers are lingering near the base of the snowpack. These layers are most likely to be triggered from thin or variable snowpack areas or with a large load like a cornice fall.

Travel and Terrain Advice
  • Avoid steep convexities or areas with a thin or variable snowpack.
  • Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.

Avalanche Summary

Over the past week there have been reports of both natural and skier triggered loose dry avalanches in steep terrain, as well as skier and explosive triggered storm slab avalanches up to size 1 that were reported on Monday.

Last weekend there were two reports of snowmobilers triggering a size 1.5 and size 2 wind slab releases on northeast to east aspects between 2000-2100 m in the Window mountain area.

Snowpack Summary

After 10-25 cm of new snow fell over Friday night, about 25-40 cm of accumulated storm snow now covers previously wind-scoured, westerly slopes and old hard and soft wind slabs on leeward, easterly alpine and treeline slopes. Beneath these old wind slabs lies a well-settled mid-pack.

The lower snowpack is generally weak with two primary concerns that are widespread:

1) A widespread weak layer from mid-December composed of facets, crusts, and surface hoar that is 100-150 cm deep.

2) A rain crust with sugary facets buried in late November near the bottom of the snowpack.

Weather Forecast

Sunday: A mix of sun and cloud with greater cloud cover in the east of the region. Light southwest winds. Alpine high temperatures of -10.

Monday: Mainly cloudy with isolated light flurries and a trace of new snow. Moderate southwest winds. Alpine high temperatures of -11.

Tuesday: A mix of sun and cloud. Light southwest winds, increasing in the afternoon. Alpine high temperatures of -12.

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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