Avalanche Forecast
North Columbia
Storm slabs, persistent slabs and weak cornices make for a complex snowpack. I'd continue to choose conservative terrain and limit my exposure to overhead hazards.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.
- Avoid steep convexities or areas with a thin or variable snowpack.
- Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
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 forecast strong northwest winds on Thursday.
Travel and Terrain Advice
- Stay off recent wind loaded areas until the slope has had a chance to stabilize.
- If triggered, wind slabs may step down to deeper layers resulting in large avalanches.
- The new snow may require several days to settle and stabilize.
Avalanche Summary
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, this avalanche points to the continued reactivity and destructive potential of these layers. On the same day, explosives control in the Monashees triggered more persistent slab avalanche activity to size 3 in north to east facing alpine terrain. Recently formed wind slabs to size 2 were also ski cut in wind-exposed, higher elevation terrain.
Observations on Tuesday were more limited due to inclement weather, although I'm sure there was a natural storm slab cycle in response to new snow and wind.
Snowpack Summary
By Wednesday morning up to 37cm of new snow had fallen. Wind data has been sparse, although I suspect strong winds 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
Thursday: Mainly clear skies / Moderate to strong northwest winds / Alpine temperature of -18
Friday: Overcast skies with light flurries / Moderate to strong westerly winds / Alpine temperature of -12
Saturday: 3-8cm of new snow / Light and variable winds / Alpine temperature of -14
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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.