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Avalanche Forecast

Archived

Jan 28th, 2012–Jan 29th, 2012

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

Regions

South Coast.

Confidence

Fair - Intensity of incoming weather is uncertain on Sunday

Weather Forecast

Sunday: light to moderate snowfall on Saturday night becoming light on Sunday / strong southwest winds decreasing in the afternoon / freezing levels reaching 1300m Monday: light flurries / moderate west winds / freezing level at 800m Tuesday: light flurries / light southwest winds / freezing level at 900m

Avalanche Summary

On Friday explosives testing in the Duffey Lake area produced avalanches to size 2.5. In the Coquihalla area, explosives control produced numerous size 2-3 avalanches with crowns ranging from 30-150cm.

Snowpack Summary

Friday and Saturday saw little in the way of new snow for the South Coast Inland region, but the big story in the region has been moderate to heavy snowfall and fluctuating freezing levels over the past week accompanied by generally high winds. It seems that as soon as one storm interface starts to strengthen, another system comes in and creates new destructive wind and storm slabs. Adding to the complexity of the storm slab problem is the January 20th interface where facetted snow from the mid-January cold snap acts as a bed surface for all of this past week's snow. A profile from the Coquihalla area also showed facets existing in combination with an underlying crust about 1m down. The probability of any activity at this interface is decreasing, but the consequences of a slide would be large and very destructive.With the recent wind and snowfall there are widespread unstable cornices. Any cornice fall would be destructive by itself, but could also be a trigger for the slope below. Persistent weak layers lower down in the snowpack have generally ceased to be of concern, except perhaps in very isolated, thin rocky areas. Most recently, the Coquihalla area has been receiving the most snowfall with current snowpack depths at treeline amounting to 390cm. In the Duffey Lake area, treeline depths are closer to 240cm.Expect continued wind slab development with forecast weather on Sunday.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.