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Avalanche Forecast

Archived

Mar 17th, 2013–Mar 18th, 2013

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

Regions

Little Yoho.

The new storm snow today has added to the touchy avalanche conditions at and above treeline. Conservative terrain choice is still required. Below  treeline the colder temps will freeze the wet snow and lower the danger.

Weather Forecast

A short lived ridge Tuesday will be followed by a progressive pattern with some precipitation, strong westerlies  and moderate temps

Snowpack Summary

Another 10-35cm of storm snow fell with the passing of the arctic air bringing the total this week to near 60 in most alpine areas. Large cornices and storm slabs exist at treeline and above with touchy slabs. Below treeline, the rain line was at nearly 2000 metres, and the snow is still wet below a weak crust that will freeze with cold temps.

Avalanche Summary

A widespread avalanche cycle has been occurring over the last few days. Slabs have been observed to size three failing both with cornice fall, wind and wet conditions. Avalanche control today produced some deep slabs and large cornice falls with several size three avalanches with crowns over 1M thick.

Confidence

Timing or intensity of solar radiation is uncertain on Tuesday

Problems

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.