North Columbia

A storm is forming new slabs and rapidly loading a buried weak layer. We are expecting an avalanche cycle in the coming days.

THURSDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, 20 to 40 km/h southwest wind, alpine temperature -9 C.

FRIDAY: Cloudy with snowfall, accumulation 10 to 20 cm, 30 to 50 km/h southwest wind, alpine temperature -7 C.

SATURDAY: Cloudy with snowfall, accumulation 10 to 20 cm, 30 to 50 km/h southwest wind, alpine temperature -8 C, freezing level rising to 1000 m.

SUNDAY: Mix of sun and cloud with no precipitation, 20 to 40 km/h southwest wind, alpine temperature -2 C, freezing level rising to 1400 m.

A handful more storm and wind slabs were triggered by riders, naturally, and explosives on Wednesday to add to the many avalanches observed in the previous few days. Most of the storm slabs released on the surface hoar layer described in the Snowpack Summary, often occurring between around 1700 and 2200 m on east, north, and west aspects. Check out some good example photos here. 

Natural and rider-triggered avalanche activity is expected to spike during Friday and into the weekend. Large avalanches are expected in areas where the buried surface hoar described in the Snowpack Summary exists. Avoidance of avalanche terrain is your best bet for having a safe day.

Around 15 to 30 cm of snow is forecast over Friday with locally higher amounts possible. The snow will form new storm slabs in areas sheltered from the wind and wind slabs in exposed terrain at higher elevations. 

The snow will load a weak layer of surface hoar crystals 5 to 15 mm in size. The layer may be around 60 to 90 cm deep by the end of Friday, which is a prime depth for human triggering. The layer is most prominent in areas sheltered from the wind. Example terrain features to treat as suspect include the lee side of protected ridges, openings in the trees, cut blocks, and burns. The layer may not exist on steep sun-exposed slopes, where a melt-freeze crust may be found instead.

The facet/crust layer that formed in early December is buried around 120 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. Humans are unlikely to trigger it, with perhaps the exception in thin, shallow snowpack areas. Check out the forecaster blog for more information.

• Travel in alpine terrain is not recommended.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
• Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
• Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
• Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
• Watch for fresh storm slabs building throughout the day.