North Columbia

 The recent snow is loading a buried weak layer. Given the uncertainty on where exactly this layer may be buried and how the recent snow will influence it, your best bet is to avoid consequential avalanche terrain and give it some time.

FRIDAY NIGHT: Cloudy with snowfall, accumulation 10 to 15 cm, 30 to 50 km/h southwest wind, alpine temperature -7 C.

SATURDAY: Cloudy with snowfall, accumulation 2 to 5 cm, 20 to 40 km/h southwest wind, alpine temperature -8 C, freezing level 1000 m.

SUNDAY: Mix of sun and cloud with no precipitation, 20 to 30 km/h southwest wind, alpine temperature -3 C, freezing level rising to 1500 m.

MONDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 40 km/h southwest wind, alpine temperature -5 C, freezing level 1400 m.

A handful more storm and wind slabs were triggered by riders on Thursday 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 Friday night into Saturday morning during the peak of the storm. Large avalanches are expected to be easily triggered by riders on Saturday in areas where the buried surface hoar described in the Snowpack Summary exists. Avoidance of avalanche terrain, particularly where the surface hoar may exist, is your best bet for having a safe day.

Storm totals may reach 20 to 40 cm by Saturday with locally higher amounts possible. The snow has formed new storm slabs in areas sheltered from the wind and wind slabs in exposed terrain at higher elevations from strong south to southwest wind. 

The snow is loading a weak layer of surface hoar crystals 5 to 15 mm in size. Forecast warming may also increase the likelihood of triggering a slab. The layer may be around 60 to 100 cm deep, 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 all avalanche terrain during periods of heavy loading from new snow and wind.
• Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
• Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.