Avalanche Forecast

Archived

Mar 13th, 2025–Mar 14th, 2025

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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Purcells, East Purcell, St. Mary.

Assess how the new snow is bonding to underlying layers, especially in wind-loaded areas.

A buried persistent weak layer means avalanches could step down and become larger than expected.

Confidence

Moderate

Avalanche Summary

Thurs: A naturally-triggered deep persistent slab occurred near Invermere, 30-100 cm deep.

Tues: Avalanche control produced large avalanches (up to size 3.5) in the central-western part of the region.

Mon: Extensive avalanche activity with storm and wind slabs, some notably stepping down to deeper persistent weak layers.

Looking forward: We expect both wind slabs and persistent slabs to remain triggerable over the following days.

Snowpack Summary

Up to 25 cm of recent snow has formed fresh wind slabs near ridgetops on leeward north through east facing slopes, driven by southwest winds. The new snow sits on a sun crust on solar aspects, and surface hoar or facets in sheltered areas or north aspects. At lower elevations the snow surface may be moist or crusty. A few weak layers consisting of a crust, facets or surface hoar from February and January remain a concern, buried 30 to 60 cm. A layer of facets from early December is buried 70 to 120 cm. In many areas, facets or depth hoar make up the base of the snowpack.

Weather Summary

Thursday Night

Partly cloudy with trace amounts of snow possible. 15 to 30 km/h southwest ridgetop winds. Treeline temperature -10 °C.

Friday

A mix of sun and clouds. 15 km/h southwest ridgetop winds. Treeline temperature -7 °C.

Saturday

A mix of sun and cloud, with isolated flurries up to 2 cm. 10 to 15 km/h south ridgetop winds. Treeline temperature -6 °C.

Sunday

A mix of sun and cloud. 10 to 15 km/h southwest ridgetop winds. Treeline temperature -5 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Be aware of the potential for large, destructive avalanches due to deeply buried weak layers.
Avoid steep, rocky, and wind-affected areas where triggering slabs is more likely.
Be careful with wind-loaded pockets, especially near ridge crests and rollovers.

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.