Purcells

Triggering large persistent slab avalanches is a serious concern this weekend. Conservative terrain choices are strongly recommended.

We are within a period of significant avalanche activity in the Purcells, with many notable large persistent slab avalanches. Buried weak layers have been easily triggered with explosives and by riders, with several size 2 to 3 slabs reported Tuesday to Saturday. These avalanches have mostly been in alpine terrain and have propagated widely across terrain features.

Triggering large persistent slab avalanches may remain a concern for a while within this region.

Roughly 40 cm of recent snow has settled into a slab. This snow may contain a rain crust at elevations below 2000 m. The additional load of this recent snowfall has stressed multiple weak layers including:

• A facet and surface hoar layer directly beneath the recent snow

• A surface hoar layer buried in mid-December that is 40 to 60 cm deep

• Weak faceted snow and decomposing crusts near the bottom of the snowpack (ranging from 70 to 150 cm deep)

These layers have shown signs of instability over the past week and need more time to strengthen.

Saturday Night

Partly cloudy with trace precipitation, 10 to 20 km/h west wind, treeline temperature -8 °C.

Sunday

Mix of sun and cloud with no precipitation, 10 km/h west wind, treeline temperature -9 °C, freezing level 900 m.

Mix of sun and cloud with no precipitation, 10 km/h southwest wind, treeline temperature -6 °C.

Sunny with no precipitation, 10 km/h southwest wind, treeline temperature -5 °C.

More details can be found in the Mountain Weather Forecast.

• Choose conservative terrain and watch for clues of instability.
• Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
• Remote triggering is a concern, watch out for adjacent and overhead slopes.
• Back off if you encounter whumpfing, hollow sounds, or shooting cracks.