Avalanche Forecast

South Rockies

Date issued

Feb 21, 2018 - 4:28 PM

Valid until

Feb 22, 2018 - 2:00 PM

Prepared by

pgoddard

Caution if the sun comes out - avoid steep sunny slopes where the snow will lose cohesion.

Regular season
Wednesday - February 21, 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 - February 22, 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 - February 23, 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: Wind Slabs

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

Wind slabs may be found on a variety of slopes at and above treeline.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Avoid steep slopes below cornices.
  • Travel on ridgetops to avoid wind slabs on slopes below.

Avalanche Problem 2: Deep Persistent Slabs

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

Deeply buried weak 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.
  • Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.

Avalanche Summary

It's been fairly quiet the last couple of days, with only reports of explosives triggering one size 2 wind slab.

On Monday, large (size 2) wind slab avalanches were triggered by skier and explosive activity, 30 to 50 cm deep. A deep persistent slab was also noted in the region, likely releasing on one of the layers described in the snowpack discussion.

It is still possible to trigger a wind slab with the weight of a person. If the sun is shining, avoid exposure to steep solar aspects where loose wet avalanche activity is possible.

Snowpack Summary

You are likely to find variable surfaces in open terrain after recent strong winds took out their fury on the upper snowpack. Fragile cornices and hard and soft wind slabs can be found on many alpine and treeline slopes. Ongoing cold temperatures are helping to break down and soften these.

A crust/surface hoar interface is about 40-60 cm down, but little is known about its sensitivity and distribution.

The lower snowpack in this region is weak with two primary concerns:

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.

Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.

Weather Forecast

THURSDAY: Mix of sun and cloud with the chance of a flurry. Freezing level at valley floor. Light winds.

FRIDAY: Mix of sun and cloud. Freezing level at valley floor. Light winds.

SATURDAY: Mix of sun and cloud. Freezing level at valley floor. Light 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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