Avalanche Forecast
South Columbia
The recent storm snow has been particularly reactive as indicated by a number of recent human-triggered avalanches. Brace for another storm on 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.
- Stay off recent wind loaded areas until the slope has had a chance to stabilize.
- If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.
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 the runout zones of avalanche paths. Very large avalanches have been running full path.
- Avoid steep convexities or areas with a thin or variable snowpack.
Avalanche Summary
On Wednesday, at least five human-triggered avalanches were reported up to size 2 on north, east and south-facing slopes and elevations between 1800 and 2300 m. The releases appeared to be at the base of the most recent storm snow and a crust was reported in some of them, most likely those on more southerly aspects. 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. On the same day, a helicopter remotely triggered a size 3 persistent slab avalanche on a similar aspect/ elevation in the Selkirks a little closer to Revelstoke. Although deeper, persistent avalanche activity is becoming less frequent, these recent avalanches point to the continued reactivity and destructive potential of these layers.
Snowpack Summary
30cm 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/ crust layers buried in January can be found. Expect to find one or the 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 800 m. Westerly ridgetop winds gusting to 40 km/h.
Saturday: 15-25 cm new snow. Treeline temperature around -10C. Winds southwesterly 30km/h.
Sunday: Clearing, but lingering flurries possible. Treeline temperatures around -14C. Winds light northeasterly.
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New storm slabs may be 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 northwest winds on Thursday.