Regions
Kootenay Boundary.
Cold north winds have been blowing. Areas with wind slabs (south through northwest aspects) may have elevated danger.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
The arctic outbreak continues with cold temperatures and no snow until Saturday afternoon at the earliest.THURSDAY: A mix of sun and cloud. Wind light southwest. Temperatures between -13 and -24 Celcius. No precipitation.FRIDAY: Cloudy with sunny periods. Winds southerly 5-15 km/h. Temperatures between -12 and -22 Celcius. No precipitation.SATURDAY: Increasing clouds in the afternoon with a slight chance of flurries. Winds light southeasterly 5-15 km/h. Temperatures between -12 and -20 Celcius.
Avalanche Summary
We've had reports of several skier-triggered windslabs (Size 1.5-2) yesterday in the backcountry near Nelson, and some natural activity the day before. Aspects were southwest through north at treeline and in the alpine.
Snowpack Summary
The snow from last week (30-60 cm) has been exposed to east through northerly winds during this cold clear period. In many areas "reverse loading" occurred, causing windslabs to form and giving sudden planar results in snowpack tests. The most recent snow sits over a weak layer buried on Boxing Day that was initially reactive but now appears to have gained strength. Slightly lower in the snowpack is an interface buried mid-December, now down 40-100 cm. This layer appears to be well bonded in many parts of the region but was reactive for a while last week west of Trail and Castlegar where preserved surface hoar was thought to be responsible for four small (but surprising) skier trigger avalanches. It will be important to continue to monitor this layer for further signs of reactivity.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.