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Avalanche Forecast

Archived

Feb 3rd, 2017–Feb 4th, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Cariboos.

A storm impacting the south of the province won't send much new snow our way. New wind slabs and a lingering persistent slab problem remain the primary concerns.

Confidence

Moderate -

Weather Forecast

Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light from the northeast. Alpine temperatures around -20.Sunday: A mix of sun and cloud with isolated flurries and a trace of new snow. Winds light from the northeast. Alpine temperatures around -20.Monday: A mix of sun and cloud with isolated flurries and a trace of new snow. Winds light from the northeast. Alpine temperatures around -20.

Avalanche Summary

Reports from Thursday include details of a remote triggered size 2.5 avalanche that occurred in the south of the region. The slide took place on a roughly 30 degree south-facing slope at 2100 m in elevation. The remote trigger, a depth of 80 cm, and a failure plane attributed to our January 15 surface hoar all reinforce enduring concerns for persistent slab problems in the region.On Monday, several natural wind slab and storm slab avalanches up to size 2.5 were reported. These slabs were typically 30-50 cm thick and failed on a variety of aspects at treeline and in the alpine. Fresh wind slabs have since been (and are expected to remain) sensitive to light triggers, especially on steep and unsupported (convex) slopes.Persistent slab avalanches remain a serious concern for the region. Last week people triggered numerous large avalanches, several of which resulted in multiple burials. These avalanches all released on, or stepped down to, the mid-December persistent weakness down 1-1.5 m in the snowpack. Check out this list of recent near misses which includes many in the Cariboo region.

Snowpack Summary

10-60 cm of recent snow (with the largest amounts in northern parts of the region) and strong shifting winds have resulted in fresh wind slabs on a variety of aspects in wind exposed terrain. Meanwhile, cold temperatures have promoted both the faceting of surface snow as well as the growth of surface hoar on sheltered open slopes. The persistent weakness buried mid-January is now down 50-100 cm and consists of buried surface hoar in sheltered areas, and/or widespread faceted old snow. It has generally stabilized but may remain sensitive to human triggers in isolated areas, especially where buried surface hoar is preserved. Another surface hoar/facet weakness was buried mid-December and can now be found down 70 cm in shallow snowpack areas, or as much as 1.5 m in deeper snowpack areas. It woke up during the last storm and has remained reactive to human triggers. This weak layer is responsible for several large human-triggered avalanches, including some with multiple burials, and the layer may remain reactive for the foreseeable future. Click here for a new blog post with more details.

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.