Avalanche Forecast

South Rockies

Date issued

Dec 9, 2017 - 3:25 PM

Valid until

Dec 10, 2017 - 2:00 PM

Prepared by

jlammers

Weaknesses deep in the snowpack will heal much more slowly than wind slabs. As alpine temperatures rise, keep your guard up around big overhead terrain and in thin snowpack areas.

Regular season
Saturday - December 9, 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

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 - December 10, 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

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.

Monday - December 11, 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

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?

A recent wind shift from southwest to north means that wind slabs now exist on a wide range of aspects at higher elevations. Be especially cautious of reverse loaded or cross-loaded slopes that see sun exposure.

Travel and Terrain Advice
  • Use ridges or ribs to avoid pockets of wind loaded snow.
  • If triggered, wind slabs may step down to deeper layers and result in large avalanches.

Avalanche Problem 2: Deep Persistent Slabs

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

Several persistent weak layers exist at the base of the snowpack. The likelihood of triggering one of these weaknesses will be elevated while warm weather persists at higher elevations.

Travel and Terrain Advice
  • Be aware of triggering thin areas that may propagate to deep instabilites more easily.
  • Minimize your exposure to overhead avalanche terrain.

Avalanche Problem 3: Loose Wet

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

Warm, sun-exposed slopes could continue to produce wet loose avalanches either naturally or with rider triggers on Sunday, especially in steeper terrain.

Travel and Terrain Advice
  • Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
  • Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.

Avalanche Summary

No new avalanches have been reported from this region. Although warm daytime temperatures and overnight cooling are likely helping bond recent wind slabs to the surface, the potential for releases deeper in the snowpack will remain elevated as these warm temperatures persist. Thin and variable snowpack depth areas will be the most likely trigger points for a deep release.

Please submit your observations to the Mountain Information Network.

Snowpack Summary

Solar and temperature crusts are expected to have formed on some surfaces over the past few days. In shaded higher elevation terrain where surface snow remained cold and unconsolidated, recent shifting winds redistributed loose snow forming stiff wind slabs on a wide range of aspects at treeline and above.

The two crusts that were buried near the end of November can now be found approximately 30 cm and 60 cm down. A third crust from the end of October exists as a "facet/crust" combo near the base of the snowpack. Snowpack testing in the adjacent Kananaskis Country forecast region has yielded hard but sudden results on this layer.

Average snowpack depths at upper elevations in the region range from about 50-100 cm.

Weather Forecast

Expect mainly clear skies and a temperature inversion for the forecast period. Alpine temperatures are expected to reach 2 degrees on Sunday and then climb to 5 degrees on Monday and Tuesday. Ridgetop winds are forecast to be moderate from the southwest on Sunday, becoming light on Monday and Tuesday.

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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