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Avalanche Forecast

Archived

Feb 1st, 2012–Feb 2nd, 2012

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

Regions

South Coast.

Confidence

Fair - Freezing levels are uncertain on Friday

Weather Forecast

A ridge of high pressure moving in from the coast is expected to produce light southerly winds combined with broken skies and freezing levels rising to about 1300 metres by Thursday afternoon. Warm temperatures are forecast to persist through the night and into Friday morning. More clearing is expected on Friday. Freezing levels are expected to rise to about 1700 metres, and solar radiation should be strong on sun exposed slopes. Alpine temperatures are forecast to be around -3.0 in the alpine. Saturday is expected to be mostly clear with temperatures a few degrees cooler than Friday.

Avalanche Summary

Numerous size 1.0 loose dry sloughs reported from the 12 cm of new snow that fell in "power flurries" in the Duffey Lake area. When the sun popped out it caused loose snow naturals on east and south aspects.

Snowpack Summary

Another 10-15 cm fell in the region on Tuesday night and Wednesday morning, adding to the weekend storm snow. During the weekend storm, rain fell to about 1700m, but freezing levels fluctuated during the storm. In the Duffey Lake area light amounts of more recent snow now sit above a new rain crust that has formed below 1700m while fresh soft wind slabs rest over cohesive stubborn wind slabs at higher elevations. In the Coquihalla area temperatures have been slower to drop. The warmer present temperatures combined with the higher snowfall/rain values in this area means that deep wind slabs have been slower to stabilize. More recent soft wind slabs now sit on top. 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.

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.