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Avalanche Forecast

Archived

Mar 20th, 2023–Mar 21st, 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.

Regions

Northwest Coastal, Kitimat, Nass, Rupert, Seven Sisters, Shames, Stewart, Howson.

Hazard is improving as temperatures drop down to the valley bottom but be mindful that buried surface hoar continues to be reactive, especially in wind loaded features.

Confidence

Moderate

Avalanche Summary

On Sunday, two, natural size 3 persistent slab avalanches were observed. Both these avalanches ran to valley bottom and are suspected to have released on a weak layer of surface hoar. Two, size 1.5 persistent slab avalanches were remotely triggered by a helicopter on the same layer.

On Saturday, numerous loose wet to size 1.5 were observed in steep, rocky solar terrain. Several natural storm slab avalanches were observed up to size 2.5, likely triggered by the sun or cornice failure. A few skier triggered, size 1, avalanches were reported. These avalanches released on a weak layer of surface hoar underneath the storm snow.

Snowpack Summary

Storm snow has settled with warm temperatures. A melt freeze crust or moist snow exists on the surface at low elevations and on sun affected slopes.

A weak layer of surface hoar is found 20-50 cm down in sheltered terrain. On solar aspects, this layer appears as a melt-freeze crust. This layer continues to be reactive to skier traffic.

A second weak layer of surface hoar and/or faceted grains may be found about 60 cm deep, particularly on shaded aspects near treeline.

The remainder of the snowpack is consolidated and strong.

Weather Summary

Monday Night

Partly cloudy. Light southwest winds at ridgetop. Treeline temperature low 0°C. Freezing levels 1500 m.

Tuesday

Mainly cloudy with isolated flurries, trace accumulation. Light southwest winds at ridgetop. Treeline temperature -1°C. Freezing levels 1200 m.

Wednesday

Mix of sun and cloud. Moderate southwest winds at ridgetop. Treeline temperature -2°C. Freezing levels 1000 m.

Thursday

Mainly sunny. Strong southwest winds at ridgetop. Treeline temperature -1°C. Freezing levels 1200 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be carefull around freshly wind loaded features.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

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.