Avalanche Forecast

South Rockies

Date issued

Jan 12, 2018 - 4:33 PM

Valid until

Jan 13, 2018 - 2:00 PM

Prepared by

mconlan

A Special Public Avalanche Warning is in effect for this region. Widespread, large avalanche activity is possible on touchy buried weak layers. Don't overthink it - maintain very conservative terrain choices and avoid overhead exposure.

Regular season
Friday - January 12, 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

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

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.

Saturday - January 13, 2018
Alpine

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.

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

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.

Sunday - January 14, 2018
Alpine

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.

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

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.

Avalanche Problem 1: Storm Slabs

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

Recent snow is likely to fail as loose snow or slab avalanches, especially in steep alpine and treeline terrain or open slopes below treeline. Snow may be deeper in lee features due to strong southwesterly winds.

Travel and Terrain Advice
  • Use conservative route selection. Choose moderate angled and supported terrain with low consequence.
  • Use caution when entering lee areas. Recent wind loading may have created wind slabs.

Avalanche Problem 2: Persistent Slabs

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

Forecasted warm air temperatures could increase the likelihood of triggering buried weak layers. The trees may not be the safe haven you expect: adopt a cautious attitude to all avalanche terrain.

Travel and Terrain Advice
  • Avoid open slopes and convex rolls where buried weak layers may be preserved.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Minimize overhead exposure during periods of warming and/or direct sun on starting zones.

Avalanche Summary

The recent 40 cm of snow has been reactive and produced small to large slabs or loose dry avalanches. One release stepped down to the early-season rain crust and facet layer. Storm slabs have most often been observed in direct lee features and steep slopes. Around 1900 m, ongoing reports of touchy conditions have been noted, such as whumpfing and cracking, which is indicative of touchy buried weak layers.

Snowpack Summary

An unstable weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below treeline elevations. Slabs can fail easily on this layer, either naturally or with the weight of a person or machine. Forecasted warm air temperatures could increase slab properties of the overlying snow and make this layer easier to trigger.

The snowpack is variable across the region, but persistent slabs are generally a widespread problem. Wind slab and storm slab distribution will be more variable. New wind slabs can be found in parts of the region due to recent southwest winds. Windward alpine slopes may be scoured; and variable wind slabs are found at treeline and alpine elevations. New snow is likely to fail as storm slabs and/or loose avalanches.

Deeper in the snowpack, an early-season rain crust and sugary facets exist. An avalanche in motion could step down to these deeper layers, creating a large and destructive avalanche. Overall snowpack depths are variable across the region. It is generally shallower in the east.

Weather Forecast

SATURDAY: Early morning snowfall, accumulation 1-3 cm, then mostly sunny, moderate northwesterly winds, alpine temperature near -4 C, freezing level near 1000 m.

SUNDAY: Mostly sunny with possible valley cloud, light to moderate northwesterly winds, alpine temperature near 0 C, inversion conditions with cold valley air and above-freezing level between about 2000 m and 2500 m.

MONDAY: Mostly sunny, light southwesterly winds, alpine temperature near 0 C, freezing level near 2500 m.

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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