Avalanche Forecast

Archived

Jan 4th, 2023–Jan 5th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary, Bonnington, Kootenay Pass, Norns, Rossland, Ymir, Moyie, St. Mary.

Buried weak layers have produced large avalanches recently. Stay disciplined and stick to conservative terrain.

Confidence

Moderate

Avalanche Summary

Several large persistent slab avalanches were triggered by explosives on Monday, releasing on the weak layers described in the Snowpack Summary. They all occurred between 2100 and 2200 m, on all aspects, and were mostly between 80 and 150 cm deep. The results show us that these layers are still a concern and, if triggered, could produce large, high consequence avalanches.

Snowpack Summary

New snow falls over a surface crust on south aspects and elevations below treeline. Elsewhere, it blankets 30 to 40 cm of previous snow overlying a hard melt-freeze crust that extends up to 2000 m. Where it is robust enough to do so, this crust appears to be effectively bridging deeper instabilities, making them more difficult to trigger.

The two prominent layers of concern are a 60 to 80 cm deep surface hoar/crust layer that was buried in mid-December and an 80 to 150 cm deep surface hoar/facet layer buried in mid-November.

Weather Summary

Wednesday night

Mostly clear, southeasterly wind increasing to 30 km/h, treeline temperature around -10 °C.

Thursday

Cloudy with up to 5 cm new snow, 30 km/h southeast wind, treeline temperature around -4 °C.

Friday

Cloudy with 5-15 cm new snow, 30-40 km/h southeast wind, treeline temperature around -2 °C, freezing level 800 m.

Saturday

Cloudy, up to 5 cm new snow, southeast wind easing to 15-20 km/h, treeline temperature -1 °C, freezing level 800 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
Be mindful that deep instabilities are still present and have produced recent large avalanches.
Use conservative route selection and resist venturing out into complex terrain.
Remote triggering is a concern, avoid terrain where triggering slopes from below is possible

Problems

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.

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.