Avalanche Forecast
North Columbia
The recent storm snow has been particularly reactive as indicated by a number of recent human-triggered avalanches. Another storm is on its way for Saturday.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- The new snow may require several days to settle and stabilize.
- If triggered, wind slabs may step down to deeper layers resulting in large avalanches.
- Stay off recent wind loaded areas until the slope has had a chance to stabilize.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Human triggering may also be possible in shallow or thin, rocky areas.
Travel and Terrain Advice
- Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.
- Avoid steep convexities or areas with a thin or variable snowpack.
- Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.
Avalanche Summary
At least three small (size 1) human-triggered avalanches were reported on Wednesday, that ran in recent storm snow with crowns approximately 30 cm deep on north, east and south-facing slopes at around 2000 m. There were also two large (size 2.5) natural avalanches in alpine terrain that initiated as wind slabs but stepped down to the mid-January weak layer. In Rogers Pass on Monday, skiers remotely triggered a size 3.5 persistent slab avalanche from 40 m away on a south-facing, cross-loaded slope at 2600 m. Although deeper, persistent avalanche activity is becoming less frequent, there is still potential for these layers to react.
Snowpack Summary
35cm of recent storm snow has settled into a slab in the upper snowpack. Strong winds, most recently from the northwest, shifted these accumulations into deeper, reactive slabs in wind-exposed terrain. These accumulations overlie a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects, a rain crust below 1600m, and surface hoar on sheltered slopes.
Below the snow surface, several persistent weak layers make up a troublesome snowpack. In the top 1.5-2.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.
Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.
Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.
All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.
Weather Forecast
Friday: 5-10 cm new snow. Freezing level 400 m. Westerly ridgetop winds gusting to 40 km/h.
Saturday: 10-15 cm new snow. Treeline temperature around -10C. Winds southwesterly 20-30km/h.
Sunday: Clearing, but lingering flurries possible. Treeline temperatures around -14C. Winds light northeasterly.
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New storm slabs have been especially reactive in wind-exposed terrain, and may be slow to gain strength due to a mix of underlying weak surfaces. Watch for new wind slab development and reverse loading due to recent northwest winds.