Regions
Northwest Inland.
Wind and storm snow have formed cohesive slabs above the recently buried crust/ surface hoar layer at upper elevations. It may also be possible to trigger a buried weak layer from thin snowpack areas.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Monday
Weather Forecast
TONIGHT: Increasing cloud. Ridge wind light, southeast. Temperature -15. Freezing level valley bottom.SUNDAY: Cloudy, flurries. Accumulation 2-5 cm. Ridge wind strong, southeast. Temperature -12. Freezing level valley bottom. Alpine Inversion.MONDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind strong, southwest. Temperature -8. Freezing level 200 m.TUESDAY: Cloudy, flurries. Accumulation 2-5 cm. Ridge wind moderate, southwest. Temperature -10. Freezing level valley bottom.
Avalanche Summary
Friday there was a report of a helicopter remotely triggering a Size 2.5 wind slab from above the slope on a west aspect at 1500 m north of Kispiox.Thursday there was a report of skiers, north of Kispiox, remotely triggering a Size 2-2.5 avalanche from a safe location on a ridge that released on the adjacent slope on a northwest aspect at 1650 m. A weak layer buried late-December was the suspected failure plane.Wednesday there was a report of a skier-triggered Size 1 wind slab avalanche on a northwesterly aspect at 1650 m in the northern part of the region, east of Ningunsaw.Tuesday there were reports of easily-triggered wind slabs 30-40 cm deep releasing to Size 1 in wind-loaded areas near ridge crests in the alpine in the southern part of the region.Reports from late last week showed a notable increase in persistent slab activity at lower elevations in the Howson Range. In this area, three Size 2 releases failed on steeper terrain with remote triggers on the mid-December weak layer, found 50 cm below the surface.
Snowpack Summary
Recent light snowfalls have gradually brought 20-60 cm of new snow across the region. This new snow has buried the mid-January interface which features a crust that exists well into the alpine and isolated pockets of surface hoar in sheltered areas at lower alpine and treeline elevations. Below the mid-January interface, deeper weak layers in the snowpack include two separate crust and surface hoar layers that were buried late-December and mid-December and now lie 50-80 cm below the surface. In the past week these deeper layers have produced hard but sudden results in recent snowpack tests as well as recent large avalanches triggered from a distance.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.