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Avalanche Forecast

Archived

Mar 18th, 2014–Mar 19th, 2014

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

Regions

Cariboos.

Confidence

Fair

Weather Forecast

Wednesday: Periods of snow – 10-15 cm. The freezing level is near 1000 m and ridge winds are moderate from the W-SW. Thursday: Cloudy with flurries and sunny breaks. The freezing level is around 800 m and ridge winds are light from the NW. Friday: A mix of sun and cloud. The freezing level is around 600-800 m and ridge winds are light from the NW.

Avalanche Summary

There were a couple new reports of natural slab avalanches stepping down to buried persistent weaknesses on Monday. Some of these were on southerly aspects and likely involved buried sun crusts with avalanches up to Size 3. There was one that was accidentally skier triggered from a Northeast aspect at treeline and likely released on the mid February weak layer. A group of snowmobilers triggered a large avalanche not far from Blue River on Friday resulting in one fatality. Some information is available here.The group involved in a very close call with a size 3.5 avalanche in the Ozalenka Valley south of McBride submitted a great incident report. Check it out here. It's an excellent example of the kind of activity we've been seeing throughout the interior in the last week.

Snowpack Summary

Around 30-40 cm of recent storm snow has fallen in the past few days. Periods of strong westerly winds have probably formed fresh wind slabs in exposed lee and cross-loaded terrain. This new snow now sits on a surface hoar and/or sun crust layer. Weakness have been observed within the new snow and at the interface between the new snow and this layer. A couple other notable persistent weaknesses remain a concern in the mid-snowpack. Another surface hoar/sun crust combo buried in early March is now down around 60-80 cm. The February 10th surface hoar/facet/crust combo is 100cm - 150cm below the snow surface and widespread throughout the region. Surface avalanches in motion and cornice fall have the potential to initiate an avalanche on this deeply buried weak layer. Cornices are large and fragile.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.