Avalanche Forecast
South Columbia
Rapid warming is expected in the alpine, while persistent slab problems exist at treeline and below. Safe travel requires careful route selection. Steep, open or sparsely treed slopes are best avoided at this time.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Buried surface hoar is more likely to be preserved in sheltered openings at and below tree line.
- Watch for signs of slab formation, such as wind effect, whumpfing, or shooting cracks.
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. Especially at treeline, a small initial slide could step down to the persistent weak layer below.
Travel and Terrain Advice
- If triggered, the storm slabs may step down to deeper layers resulting in larger avalanches.
- Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.
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 60-100cm.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
Tuesday: Cold air in the valleys, warmer air up high. An above freezing layer is expected from approximately 2000-2500 m. Some valley cloud is possible, clear at upper elevations. Light westerly winds.
Wednesday: basically a repeat of Tuesday, possibly slightly warmer.
Thursday: Cloud developing. Lower elevations are finally expected to start to warm, although the above freezing layer is expected to remain in place. Light southwesterly winds.
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A weak layer of surface hoar buried 60-100 cm deep has potential to produce large avalanches where the overlying snow has settled into a cohesive slab.