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Avalanche Forecast

Archived

Mar 18th, 2025–Mar 19th, 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 unlikely, human triggered possible.
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.

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, Ymir, Crawford, Moyie, Kokanee, Retallack, Valhalla, Whatshan.

Numerous large rider triggered avalanches continue to be reported in this region.

Triggering is most likely at treeline and above on wind-loaded slopes.

Confidence

Moderate

Avalanche Summary

On Monday, numerous skier triggered storm slab avalanches up to size 2 were reported primarily at treeline and above on a variety of aspects. Here's one example.

A snowcat triggered a size 2.5 persistent slab avalanche on the early March Surface hoar layer on a east aspect at treeline. The avalanche stepped-down 90 cm to the late January surface hoar layer.

A cornice fall also triggered a storm slab which triggered a size 2.5 persistent slab on the early March layer.

Snowpack Summary

40 to 65 cm of recent snow and southwest winds formed slabs reactive to human triggers.

Concern remains for triggering persistent slab avalanches. These layers include:

  • Facets/surface hoar/crust from early March buried 40-70 cm.

  • Facets/surface hoar/crust from mid-February buried 60-100 cm

  • Facets/surface hoar/crust from late January buried 100-160 cm.

The lower snowpack is well settled and strong.

Weather Summary

Tuesday Night

Clear skies, 10 to 20 km/h southwest ridgetop winds, treeline temperature -8 °C, freezing level valley bottom.

Wednesday

Mix of sun and cloud, 30 to 40 km/h south ridgetop winds, treeline temperature -5 °C, freezing level 1400 m.

Thursday

Cloudy with flurries, 5-10 cm snow, 20 to 30 km/h southwest ridgetop winds, treeline temperature -4 °C, freezing level 1500 m.

Friday

Snow, 10-20 cm, 30 to 40 km/h southwest ridgetop winds, treeline temperature -4 °C, freezing level 1500 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Remote triggering is a concern; avoid terrain where triggering overhead slopes is possible.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks, or recent avalanches.
  • Use small, low consequence slopes to test the bond of the new snow.
  • Be aware of the potential for larger than expected storm slabs due to buried surface hoar.
  • Avoid steep, sun-exposed slopes when the air temperature is warm or when solar radiation is strong.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.