Avalanche Forecast

South Rockies

Date issued

Dec 10, 2017 - 3:42 PM

Valid until

Dec 11, 2017 - 2:00 PM

Prepared by

jlammers

Warm temperatures and solar radiation may elevate the avalanche danger at higher elevations on Monday.

Regular season
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.

Tuesday - December 12, 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

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.

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?

Variable winds from last week have formed wind slabs 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
  • If triggered, wind slabs may step down to deeper layers and result in large avalanches.
  • Use ridges or ribs to avoid pockets of wind loaded snow.
  • Be alert to conditions that change with elevation.

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
  • Minimize your exposure to overhead avalanche terrain.
  • Be aware of triggering thin areas that may propagate to deep instabilities more easily.

Avalanche Problem 3: Loose Wet

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

The band of warm air associated with the inversion has been hovering at elevations higher than most peaks in the area. If this band of warm air drops, we may see a round of loose wet avalanche activity in steep, sun-exposed terrain.

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

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. The band of warm air associated with the inversion has been hovering at elevations higher than most peaks in the area. If this band of warm air drops, we may see a round of loose wet avalanche activity in steep, sun-exposed terrain.

Please submit your observations to the Mountain Information Network.

Snowpack Summary

Stiff wind slabs exist on a wide range of aspects in alpine and exposed treeline terrain. On sheltered treeline and below treeline slopes, I suspect light amounts of low-density snow intermingle with surface hoar and surface facets.

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 valley cloud for the forecast period. An inversion is forecast for all 3 days with high alpine temperatures peaking at 5 degrees on Monday and Tuesday. Winds are expected to remain light to moderate from the west.

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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