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Avalanche Forecast

Archived

Mar 23rd, 2013–Mar 24th, 2013

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

Regions

Cariboos.

Very large cornices have been falling off naturally and triggered by people moving near them. Expect cornices to continue to fall during this period of sunny weather.

Confidence

Good

Weather Forecast

Overnight and Sunday: Some convective energy may cause localised flurries with little accumulation overnight. Convective energy should be reduced on Sunday as the High pressure system moves over the Interior. Expect mostly sunny skies with light Southwest winds and freezing levels rising to about 1300 metres. Strong solar radiation may cause moist snow up to 2100 metres on Southerly aspects.Monday: The surface ridge of High pressure should stay mostly intact as it slides a bit to the East. Expect mostly sunny skies with light Southwest winds and freezing levels rising to about 1400 metres.Tuesday: Some cloud is expected to drift into the interior from a weak disturbance on the coast. There is a chance of flurries that may accumulate a couple of cms.

Avalanche Summary

Natural cornice falls up to size 3.0 were reported from Thursday. Some of these avalanches entrained a lot of snow in the tracks, but did not step down to deeply buried weak layers (March 10th surface hoar/facet ).

Snowpack Summary

Cornices are reported to be very large and weakly bonded. Natural cornice falls are a concern during daytime warming. Cornices may also be triggered easily by travelling near them. Slopes with corniced entrances, or exposed to cornice falls should be avoided with these conditions. Dry windslabs may be found on Northwest thru Northeast aspects at higher elevations. These wind slabs are reported to be improving their bond to the old surface, but may continue to be triggered by skiers and riders. Loose moist or wet snow may fall naturally out of very steep terrain on sun exposed slopes. Small loose snow avalanches may trigger the recent storm snow slab where it is moist from solar heating and sitting on a planar sliding surface like an old sun or rain crust. The weak layer of buried surface hoar from March 10th is down more than a metre in most places, and is reported to require hard forces to result in resistant failures in snow profile tests. The lower snowpack consists of well bonded layers that are well settled and strong.

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.

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.