Avalanche Forecast

South Rockies

Date issued

Dec 5, 2017 - 4:30 PM

Valid until

Dec 6, 2017 - 2:00 PM

Prepared by

cgarritty

Change is in the air with strong solar effect and the beginning of a warming trend in the forecast. These two factors will begin to undermine stability on Wednesday.

Regular season
Tuesday - December 5, 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.

Wednesday - December 6, 2017
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

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.

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 - December 7, 2017
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

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.

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?

Stiff wind slabs could be reactive to rider triggers at treeline and in the alpine on leeward and cross-loaded slopes. Be especially cautious of cross-loaded slopes that see sun exposure on Wednesday.

Travel and Terrain Advice
  • Watch for whumpfing, hollow sounds, and shooting cracks.
  • Use ridges or ribs to avoid pockets of wind loaded snow.

Avalanche Problem 2: Persistent Slabs

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

There are several crusts now buried within the snowpack. Use extra caution in thin snowpack areas where it may be possible to trigger a deeper layer. Triggering a wind slab may also have the potential to step-down to a deeper layer.

Travel and Terrain Advice
  • If triggered, wind slabs may step down to deeper layers and result in large avalanches.
  • Be aware of triggering thin areas that may propagate to deep instabilites more easily.

Avalanche Summary

No new avalanches have been reported from this region. There is potential for triggering wind slabs on leeward slopes and dry loose avalanches from steeper terrain features. Smaller avalanches may also step down and trigger larger avalanches on buried weak layers deeper in the snowpack. Please submit your observations to the Mountain Information Network.

Snowpack Summary

Average snowpack depths at upper elevations in the region range from 60-110 cm. Snow surfaces have been scoured on southwesterly slopes and deeper pockets of wind slab likely exist on northeasterly slopes. Below the surface, the two crusts that were buried near the end of November can now be found approximately 40 cm and 70 cm down. Deeper in the snowpack a third crust from the end of October exists as a "facet/crust" combo and has been identified as a potential sliding interface. Snowpack testing in the adjacent Kananaskis Country forecast region has yielded hard but sudden results on this layer.

Weather Forecast

Wednesday: A mix of sun and cloud. Light northwest winds. Alpine temperatures around -3 and rising in the afternoon and evening with the onset of an alpine temperature inversion.

Thursday: Mainly sunny with some valley cloud. Freezing level rising from 2700 to 3300 metres over the day with a strong temperature inversion. Alpine temperatures to about +5 with cooler temperatures at lower elevations.

Friday: Sunny. Light west winds. Freezing level remaining around 3300 metres with alpine temperatures to about +7. Cooler at lower elevations under the lingering temperature inversion.

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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