Avalanche Forecast
South Columbia
Warm alpine temperatures and a persistent weak layer 60-80 cm below the surface are both good reasons to be cautious.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Watch for signs of slab formation, such as wind effect, whumpfing, or shooting cracks.
- Buried surface hoar is more likely to be preserved in sheltered openings at and below tree line.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
As the temperature warms, recent storm snow is expected to settle into a denser slab, making triggering a small slab avalanche more likely.
Travel and Terrain Advice
- Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.
- If triggered, the storm slabs may step down to deeper layers resulting in larger avalanches.
Avalanche Summary
There have been several reports over the last couple of days of human-triggered persistent slab avalanches affecting people on mainly north and east aspects between 1500 and 2100m. In these cases, the weak layer was the mid-December layer and the average crown depth was 80 cm. There were also reports of loose dry and small storm slab avalanches being triggered in steep terrain. As the temperatures rises in the next few days, the potential for more persistent slab avalanches on the mid December weak layer will increase.
Snowpack Summary
40-70cm of low density new snow from last week has buried a layer of weak feathery surface hoar and/or sugary facets. This new snow is expected to start to consolidate into a slab once forecast warmer temperatures take effect, but so far the upper snow has been remained light and soft. Of much greater concern from an avalanche point of view is a weak layer buried mid-December that consists of surface hoar, a sun crust and/or sugary facets, and is now down approximately 60-80cm.The bond at this interface is highly variable. The most concerning areas are those that saw pronounced surface hoar development before mid-December, such as sheltered areas at and below treeline, sheltered northerly aspects in the alpine, or anywhere the surface hoar formed on top of a sun crust. Recent snowpack tests show wide ranging reactivity on this weak layer but suggest that it may be most reactive on northerly aspects. A rain crust that formed in late November is now buried 100-140cm deep. Treeline snow depths are in the region of 200 cm.
Weather Forecast
Wednesday: Cold air in the valleys, warmer air up high that is expected to get close to 0C above 2000m. Some valley cloud is possible, clear at upper elevations. Light variable winds.
Thursday: Clear in the morning, cloud developing through the day. Inversion conditions expected to persist. Moderate southwesterly winds.
Friday: Cloudy with light snow. Freezing level 500 m. Moderate southwesterly winds.
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A weak layer of surface hoar buried 60-80 cm deep has potential to produce large avalanches where the overlying snow has settled into a cohesive slab.