Avalanche Forecast

Issued: Mar 20th, 2021 4:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

Avalanche Canada mconlan, Avalanche Canada

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Strong wind is forecast on Sunday, which may form new wind slabs that could be touchy to riders during formation and into Monday. The problem will be most likely where 15+ cm of soft snow is found, so assess for new snow, strong wind, and slab characteristics during your travels.

Summary

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

SATURDAY NIGHT: Increasing cloud with overnight snowfall, accumulation 1 to 3 cm, 40 km/h southwest wind, alpine temperature -13 C.

SUNDAY: Cloudy with snowfall, accumulation 10 to 20 cm with localized areas of 30 cm possible, 40 to 60 km/h southwest wind, alpine temperature -10 C.

MONDAY: Early-morning snowfall then a mix of sun and cloud, accumulation 5 to 10 cm, 20 km/h west wind, alpine temperature -9 C.

TUESDAY: Cloudy with snowfall, accumulation 5 to 15 cm, 40 km/h southwest wind, alpine temperature -6 C.

Avalanche Summary

No new avalanches were observed on Friday. On Thursday, some large cornice failures were observed, of which some triggered small slab avalanches on the slopes below (see here). Looking forward, wind slabs are likely to be triggered by riders on Sunday at higher elevations, as new snow and strong wind are forecast.

Snowpack Summary

Around 15 to 30 cm of new snow may be found across the region by Sunday afternoon. Wind slabs are likely forming at high elevations in exposed terrain from strong southwest wind. Storm slabs may be found in steep sheltered terrain. This snow overlies a thick melt-freeze crust up to treeline and to mountain tops on sun-exposed slopes. Cornices are very large along ridgelines and always have the possibility of failing naturally or from the weight of a human.

A weak layer of facets buried mid-February may be found around 100 to 120 cm deep, or shallower in the east of the region. This layer was reactive about a week ago in the Hasler riding area (see here). The most likely place to trigger this layer is where the snowpack is shallow in alpine terrain. Large loads, such a cornice falls or multiple sleds on the same slope, often trigger slopes that single rider couldn't trigger.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Wind slabs are most reactive during their formation.
  • Avoid exposure to slopes that have cornices overhead.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid areas with a thin or variable snowpack.

Problems

Wind Slabs

An icon showing Wind Slabs

New wind slabs are expected to form as strong southwest wind blows around recent snow. You are most likely to find them in steep leeward terrain features adjacent to ridges in wind-exposed terrain at higher elevations.

Aspects: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

The persistent slab problem is most likely on the eastern slopes of the region (e.g., Kakwa, Tumbler Ridge). Large natural avalanche activity was noted around a week ago. Steep, rocky slopes with a shallow or thin to thick snowpack in the alpine are the most likely places to trigger buried weak layers. Large loads, such a cornice falls or multiple sleds on the same slope, often trigger slopes that a single rider couldn't.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

2 - 3

Valid until: Mar 22nd, 2021 4:00PM