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Avalanche Forecast

Archived

Mar 2nd, 2021–Mar 3rd, 2021

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

Regions

South Coast Inland.

The CONSIDERABLE rating reflects the potential for wet snow avalanches in the south of the region, where above freezing temperatures are forecast up to 2000m Wednesday. Further north, where freezing levels remain around 1500m, avalanche danger is MODERATE.

Confidence

Low - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Tuesday night: Partly cloudy. Moderate southerly . Freezing level 1000 to 500 m. Southwesterly wind light below 2000 m, moderate 2000-2500 m, strong above.

Wednesday: Mix of sun and cloud. Moderate southerly wind increasing to strong above 2000 m. Freezing level rising to 1500 m in the north and 2000 m in the south.

Thursday: Mix of sun and cloud. Moderate to strong southerly winds. Freezing level 1700 m in the north and 2200 m in the south.

Friday: Mix of sun and cloud. Moderate to strong southerly winds. Freezing level 1500 m.

Avalanche Summary

Natural glide slab avalanches size 2-2.5 were observed out of steep north facing paths below treeline in the Coquihalla area Monday. Glide slabs are notoriously difficult to forecast but with the warming trend ahead, we may see an uptick in activity. Glide slabs are most likely in areas of smooth ground cover such as rock slabs at lower elevations experiencing prolonged warm temperatures with limited overnight refreeze. These avalanches will be large, involving the full depth of the snowpack. Carefully consider your access/egress routes where they cross under large paths.

Over the weekend, the Coquihalla area saw heavy skier traffic. While most reports described good ski quality in the trees, one MIN reported a skier triggered wind slab on a northeast aspect around treeline.

On Sunday, a size 1.5 skier accidental was reported on a northwest aspect in the alpine near Duffey Lake. The slab is thought to have failed on a thin layer of underlying facets over the firm bed surface of old, previously wind-stiffened snow. 

Snowpack Summary

Upper elevations are wind affected throughout the region.

  • In the Coquihalla area, the snowpack is generally well consolidated with no concerns of buried weak layers.

  • In the north of the region, 15-30 cm of snow sits over a widespread layer of facets and isolated crusts. This interface is of most concern in areas where a thin layer of facets separates recent wind slab (above) and old buried hard slabs (below) which can act as a bed surface.
  • A persistent weak layer composed of a crust, facets or surface hoar depending on elevation/aspect is now down 70-120 cm. This layer, buried in late January, continues to be noted in snowpack tests with mixed results. There have been no recent avalanches reported on this layer. Large triggers, such as an avalanche in motion, cornice fall, or intense loading from snow/ wind and/or a rapid rise in temperature can awaken these deeper weak layers. The lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Avoid lingering or regrouping in runout zones.
  • Cornices become weak with daytime heating or solar exposure.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

Problems

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.