Avalanche Forecast
Purcells
Significant uncertainty exists with forecast snowfall amounts: If you see more than 30 cm of new snow, consider the danger to be HIGH and avoid all avalanche terrain, including overhead hazard.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
- If triggered storm slabs may step down to deeper layers and result in very large avalanches.
- The new snow will take time to settle and stabilize.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Several weak layers are buried in the snowpack, creating very large avalanches when triggered.
Travel and Terrain Advice
- Use conservative route selection, bearing in mind that avalanches may be surprisingly large.
- Avoid thin, rocky or sparsely-treed slopes.
- Avoid open slopes and convex rolls where buried surface hoar may be preserved.
Avalanche Summary
On Saturday near Kimberley, skiers remote-triggered two Size 2 avalanches, by a convex roll near 2000m elevation. Crown height was 60-70cm, suggesting the snow ran on the mid January layer. See the MIN report for more details.
With consistent loading into Tuesday, human triggering will remain likely and avalanches could be surprisingly large due to the structure of the snowpack.
Snowpack Summary
The current snowpack is complex, with three active weak layers that we are monitoring.
1) 60-90 cm of recent storm snow overlies a crust and/or surface hoar layer (from mid-January). The crust is reportedly widespread, except for possibly at high elevations on north aspects. The surface hoar is 10 to 30 mm in size, at all elevation bands. The recent snow fell with strong south winds, producing wind slabs and cornices in lee features.
2) Deeper in the snowpack (down 70-100 cm), a persistent weak layer known as the early-January layer is present at all elevation bands, and composed of surface hoar on sheltered slopes and sun crust on steep solar aspects. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential.
3) Another persistent weak layer that was buried mid-December is 80 to 120 cm deep and consists of a facet/surface hoar/crust combination. It is most problematic at and below tree line.
A rain crust buried in November is 100 to 150 cm deep and is likely dormant for the time being.
Weather Forecast
Tuesday: 5-15 cm snow Monday overnight into Tuesday with another 10 cm snow possible during the day. Light to moderate south-westerly winds. Alpine temperature near -6.
Wednesday: Cloudy with isolated flurries. Light south-westerly winds. Alpine temperature near -8.
Thursday: Occasional flurries. Moderate south-westerly winds. Alpine temperature near -8.
More information can be found in the Mountain Weather Forecast.
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Forecast moderate winds, heavy snowfall and warming temperatures are a recipe for widespread avalanches. A storm slab could step down to a deeper weak layer, creating a surprisingly large avalanche.