Avalanche Forecast

Archived

Mar 11th, 2025–Mar 12th, 2025

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 possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

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

Purcells, East Purcell, St. Mary.

Surface beneath the new snow varies, assess the bond as you change aspect and elevation.

Take extra care when transitioning into wind affected terrain.

Confidence

Moderate

Avalanche Summary

On Monday, there was extensive avalanche activity in the region. Large storm slab and wind slab avalanches occurred, with some stepping down to weak layers that are deeper in the snowpack, causing a persistent slab.

Notably, on March 6th, one person was buried in an avalanche in Pedley Pass, just east of the forecast area. See details about that avalanche and a few nearby in these MINs.

Snowpack Summary

Up to 20 cm of low density snow has been moderately redistributed in the alpine. This sits on a sun crust on solar aspects, and surface hoar or facets in sheltered areas or north aspects. Below treeline, a new surface crust likely exists from strong sunshine yesterday.

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 exist at the base of the snowpack. These deeper layers are not currently creating an avalanche problem.

Weather Summary

Tuesday Night

A mix of sun and cloud, with isolated flurries. 10 to 20 km/h southwest ridgetop winds. Treeline temperature -6 °C.

Wednesday

Mainly cloudy, with isolated flurries. 10 to 20 km/h southwest ridgetop winds. Treeline temperature -3 °C.

Thursday

Mainly cloudy, with up to 5 cm of snow. 10 to 25 km/h south ridgetop winds. Treeline temperature 0 °C.

Friday

A mix of sun and clouds, with flurries. 10 to 25 km/h southwest ridgetop winds. Treeline temperature -4 °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.
Pay attention to the wind; once it starts to blow, sensitive wind slabs are likely to form.

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.