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Avalanche Forecast

Archived

Feb 17th, 2023–Feb 18th, 2023

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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast Inland, Birkenhead, Duffey, South Chilcotin, Stein, Taseko.

A thin and very tricky snowpack that harbors a deep persistent slab avalanche is prevalent in this region. Employ travel techniques that focus on conservative terrain selection and minimize exposure to steep terrain features.

Avoid shallow rocky areas where the snowpack transition from thick to thin and triggering deep persistent layers is more likely.

Confidence

Moderate

Avalanche Summary

On Tuesday, several large natural deep persistent slab avalanches were reported near South Chilcotin Mountains Provincial Park and the Birkenhead area. The avalanches were up to size 3 and were likely triggered by cornices or wind. See this MIN for photos of a few of the avalanches.

Numerous small loose dry avalanches were reported to size 1.5 on all aspects. A skier accidental size 1 wind slab avalanche was reported in northeast facing alpine terrain.

On Monday afternoon, search and rescue technicians responded to a fatal avalanche incident north of the Sea to Sky region. The avalanche is believed to have occurred on Saturday and was initiated in a shallow rocky area. See the MIN for more details.

A skier remote triggered, size 2 avalanche was reported on a cross-loaded morainal feature. The group reported the avalanche as a soft wind slab over a crust. The slope fractured 30 m above the group. See the MIN for more information.

Snowpack Summary

Overnight accumulations of 5 to 15 cm add to 20 cm of recent snow. This accumulation is being actively redistributed by moderate to strong north through to northwest ridgetop winds. This overlies wind-affected surfaces at higher elevations and a crust at lower elevations. On steep solar slopes at lower elevations, a sun crust can be found on the surface.

A melt-freeze crust from late January is found down 60-80 cm. At the moment this layer appears to be gaining strength though in isolated areas small facets are still found surrounding the crust.

There is a widespread weak layer of large sugary of facets at the bottom of the snowpack. This layer has recently resulted in a handful of large destructive avalanches. These avalanches seem to be concentrated in the northern half of the region however the layer is found throughout. Snowpack depths around treeline range between 150 to 250 cm.

Weather Summary

Friday Night

Cloudy with isolated flurries, a trace of accumulation. Ridgetop winds northwest 50 km/h gusting to 100 km/h. Treeline temperature -8 °C. Freezing level rising 500 m.

Saturday

Cloudy, becoming clear mid-day, no new precipitation. Winds northwest 40 km/h. Treeline temperature -4 °C. Freezing level rising to 1100 m mid-day.

Sunday

Cloudy with isolated flurries, trace accumulation. Winds northwest 60 km/h. Treeline temperature -4 °C. Freezing level rising to 1100 m mid-day.

Monday

Cloudy with isolated flurries, trace accumulation. Winds northwest 60 km/h. Treeline temperature -2 °C. Freezing level rising to 1500 m mid-day.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.