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Avalanche Forecast

Archived

Mar 21st, 2013–Mar 22nd, 2013

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

Watch for thin areas especially East of the divide where triggering deeper slabs over facets can cause large avalanches. SH 

Weather Forecast

Light N winds, freezing levels hovering around valley bottom, and only light snow tomorrow.  We may see more sun through the weekend which may trigger an avalanche cycle on solar aspects within the new snow.

Snowpack Summary

W of Divide: Tak study plot (Yoho) today @1800m.Well settled 230cm snowpack. 30cm moist layer (rain event last week) buried under 30cm low density snow. Up to 40cm snow in last 48 hrs  at TL. (E-Mod shears).

E of Divide:harder wind slabs over a variety of surfaces from sun crust, facets, and depth hoar. Sensitive to human triggering in thin areas.

Avalanche Summary

A report of a remote triggered sz.3 in the observation peak area (East of hwy. 93 N) on a SW aspect in the alpine March 20.  It was up to 175cm deep on a basal weakness and was 200m wide.   A similar sized slide in the Redoubt area in the Lake Louise backcountry (E of Divide) occurred on the 19th.

Confidence

on Friday

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.

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.

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.