South Columbia

The recent snow loaded a buried weak layer. There is uncertainty on where exactly this layer may be buried and how the recent snow will affect it. Rising temperatures and sun on Sunday increase the likelihood for riders to trigger avalanches. Give the snowpack time to stabilize.

SATURDAY NIGHT: Clear with cloudy periods, light northwest wind, alpine temperature -1 C, above freezing layer possible around 1800 m.

SUNDAY: Mix of sun and cloud in the morning and sunny in the afternoon, light to moderate west wind, alpine temperature +1 C, freezing level rising to 2100 m.

MONDAY: Mix of sun and cloud, up to 5 cm new snow, moderate to strong west wind, alpine temperature -4 C, above freezing layer Sunday night into Monday morning from 1600 to 2300 m, freezing level around 1500 m in the afternoon.

TUESDAY: Mix of sun and cloud, up to 3 cm new snow, light to moderate southwest wind, alpine temperature -2 C, freezing level 1500 m.  

On Saturday, at the time of writing, explosives had triggered avalanches up to size 2. Several large natural slabs up to size 2.5 were observed on all aspects in the alpine. Riders triggered small wind slabs up to size 1.5 at treeline. 

Observations on Friday were limited due to visibility. A natural avalanche cycle of small slabs up to size 1.5 was observed, as well as numerous small rider triggered avalanches. Explosives triggered numerous large (size 2) avalanches. A deep persistent slab avalanche was triggered by a machine and released on the early December facet/crust layer described in the Snowpack Summary.

Many 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 1600 and 2200 m on all aspects except due south. Read this MIN for a detailed description of a skier-triggered avalanche in the south of the region -- thank you for the detailed report.

Large avalanches are still expected to be easily triggered by riders on Sunday 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.

The recent storm brought 10 to 30 cm snow. The snow has likely 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 loaded 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 40 to 80 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 100 to 200 cm. The last reported avalanche was on February 4 in the southwest of the region. 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.

• Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
• Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
• Avoid steep slopes when air temperatures are warm, or solar radiation is strong.