Avalanche Forecast

Archived

Mar 17th, 2025–Mar 18th, 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 unlikely, human triggered possible.

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.

Human triggered persistent slab avalanches continue to be reported.

Triggering is most likely on northerly aspects and in wind affected terrain.

Confidence

Moderate

Avalanche Summary

On Sunday, a skier remotely triggered a size 2 persistent slab avalanche from 50 m away. The avalanche failed on a wind loaded slope on a northerly aspect at treeline near Panorama. The weak layer was 40-150cm deep.

A naturally triggered size 2 deep persistent slab that scrubbed down to rocks was observed on northwest aspect in the alpine near Brisco.

Explosive triggered storm slabs were also reported up to size 2.5, primarily on northerly aspects in the alpine.

Snowpack Summary

30 - 50 cm of recent storm snow overlies a crust on sunny slopes and lower elevations, and surface hoar or facets on sheltered and shady upper elevations. Southwesterly wind formed slabs on lee features at treeline and above.

Several persistent weak layers consisting of a crust, facets or surface hoar from February and January remain a concern, buried 50 to 100 cm.

The bottom of the snowpack is composed of large facets in many areas.

Weather Summary

Monday Night

Partly cloudy, 10 to 20 km/h west ridgetop winds, treeline temperature -10 °C, freezing level valley bottom.

Tuesday

Mix of sun and cloud, 10 to 20 km/h west ridgetop winds, treeline temperature -6 °C, freezing level 1400 m.

Wednesday

Mostly sunny, 5 to 10 km/h southwest ridgetop winds, treeline temperature -5 °C, freezing level 1500 m.

Thursday

Cloudy, 20 to 30 km/h southwest ridgetop winds, treeline temperature -3 °C, freezing level 1700 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Avoid steep, rocky, and wind-affected areas where triggering slabs is more likely.
Be aware of the potential for large, destructive avalanches due to deeply buried weak layers.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Even brief periods of direct sun could produce natural avalanches.
Avoid steep, sun-exposed slopes when the air temperature is warm or when solar radiation is strong.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.