Avalanche Forecast

Archived

Dec 21st, 2024–Dec 22nd, 2024

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

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, Grohman, Kootenay Pass, Norns, Rossland, Ymir, Crawford, Moyie, St. Mary, Badshot-Battle, Goat, Kokanee, Retallack, Valhalla, Whatshan.

When the snowpack is the question, terrain is the answer.

Uncertainty necessitates conservative terrain selection and good travel habits.

Confidence

Moderate

Avalanche Summary

A widespread natural avalanche cycle took place during the storm last Wednesday. Following this storm, the most notable avalanche activity has been large (size 2) persistent slab avalanches failing on buried crust/facets or surface hoar.

Listen to Friday night's State of the Snowpack for more details on the snowpack and avalanche danger in the Nelson area.

Snowpack Summary

Up to 15 cm of new snow will add to 60 cm of recent storm snow. Southwest winds have redistributed this snow into deeper deposits in lee terrain features at higher elevations.

In the mid snowpack (down 40 to 100 cm) there are weak layers of facets, crusts, and in some places surface hoar. The distribution of these layers is highly variable throughout the region. The areas showing the greatest reactivity in these layers are the Goat Range, Bonningtons, and Rossland Range.

The lower snowpack is strong and bonded. Treeline snow depths range from 100 to 180 cm.

Weather Summary

Saturday Night

Cloudy with 5 to 15 cm of new snow. 20 to 50 km/h southwest ridgetop wind. Treeline temperature -4 °C.

Sunday

Cloudy with up to 2 cm of new snow. 15 to 30 km/h southwest ridgetop wind. Treeline temperature -5 °C.

Monday

Cloudy with up to 5 cm of new snow. 15 to 40 km/h southwest ridgetop wind. Treeline temperature -4 °C.

Tuesday

Cloudy with up to 15 cm of new snow. 20 to 50 km/h southwest ridgetop wind. Treeline temperature -3 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Approach steep and open slopes at and below treeline cautiously, as buried surface hoar may exist.
Surface hoar distribution is highly variable. Avoid generalizing your observations.
Be aware of the potential for large avalanches due to a buried crust.
Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.

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.