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Avalanche Forecast

Archived

Jan 31st, 2012–Feb 1st, 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 unlikely, human triggered possible.
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.

Regions

Cariboos.

Confidence

Good - -1

Weather Forecast

Wednesday: Another 5-10cm expected with light to moderate southwesterly winds and freezing levels around 1000m. Thursday and Friday: Clear and dry with significant warming by Friday and moderate northwesterly winds becoming light and variable.

Avalanche Summary

Several natural and slope-cut step down slab avalanches Size 2 to 3.5 associated with the mid-January persistent weakness as deep as 150cm occurred on Monday. Check out the incident database (link under the Bulletins tab) for a report of a slope-cut stepping down to the mid-January facets in the Monkton Creek area near Barkerville. The recent storm snow also remains sensitive to human triggers with several Size 1 to 2, 30-40cm thick slab avalanches.

Snowpack Summary

Total snowpack depths are well above average or even new record depths for this time of year. Recent warm temperatures and upside-down storms created a touchy surface slab. Other weaknesses within and under the 150+cm of recent storm snow create the potential for step-down avalanches, but things seem so be settling rapidly. Moderate southerly or southwesterly winds have created wind slabs and large fragile cornices in exposed lee and cross-loaded terrain. Snowpack test results on the mid-January persistent weakness range from no result where it's deeply buried to moderate sudden where it was found as facets overlying a crust down 80cm. This, as well as recent avalanche activity, suggests large persistent slab avalanche that propagate across entire slopes could be triggered, especially by step-down avalanches and cornice falls in shallow snowpack areas.

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.

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.

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.