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Avalanche Forecast

Archived

Feb 16th, 2023–Feb 17th, 2023

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

Regions

Sea To Sky, Brandywine, Garibaldi, Homathko, Powell River, Spearhead, Tantalus, Sasquatch.

Expect to encounter increasingly sensitive wind slabs as the incoming storm adds more mass to an already established avalanche problem. Seek well support low angle terrain that avoids steep lee aspect wind-loaded areas.

Carefully evaluate wind loading as you move through terrain and investigate the bond of wind slabs to the crust below.

Confidence

Moderate

Avalanche Summary

On Tuesday, A snowmobiler remote triggered a size 2 persistent avalanche in the Callaghan. The avalanche was reported to be triggered from 10 m away and was adjacent to a heavy traffic area. We suspect this avalanche slid on the mid-January persistent weak layer. See the MIN for details and photos. This is the latest human-triggered avalanche on this persistent weak layer in the region.

For more evidence of this weak layer see this MIN report from last Wednesday when a rider at Chocolate Bowl triggered a size 2.5 persistent avalanche. Find another example in this MIN from a skier accidental size 2 persistent slab avalanche that occurred on Saturday.

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.

Snowpack Summary

An incoming storm is expected to bring another 10 to 20 cm of new snow. This will be in addition to up to 30 cm of past storm snow. Expect the wind to redistribute this over a variety of surfaces including facets, old wind slabs, and a thin breakable crust below 1650 m. In sheltered areas above 1200 m snow remains dry and unconsolidated.

Two concerning crusts are found in the mid-pack at varying depths and are widespread throughout the region. A crust from late January is found at all elevations down 40-100 cm with small facets above it. In the Rhododendron and Pemberton Icefield area, this crust has been reactive to rider traffic and in test pits at treeline. In the Brandywine area, a crust found 80-200 cm deep resulted in a few surprisingly large rider-triggered avalanches last week. This layer exists to 1900 m in these areas.

Total snowpack depths are approaching 300 cm in some areas.

Weather Summary

Thursday Night

Mainly cloudy with snowfall, 5 to 10 cm accumulation. Winds southwest 20 km/h gusting to 50 km/h. Treeline temperature -12 °C. Freezing level 200 m.

Friday

Cloudy with light snowfall, 1 to 5 cm of accumulation. Winds Northwest 20 km/h gusting to 50 km/h. Treeline temperatures -8 °C and freezing levels of 600 m. 

Saturday

Partly cloudy with isolated flurries, 1 to 5 cm accumulation. Winds northwest 5 km/h gusting 30 km/h. Treeline temperature -6 °C. Freezing level 700 m.

Sunday

Partly cloudy with isolated flurries, 1 to 5 cm accumulation. Winds northwest 20 km/h gusting 60 km/h. Treeline temperature -6 °C. Freezing level 700 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Be alert to conditions that change throughout the day.

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.