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Avalanche Forecast

Archived

Apr 1st, 2017–Apr 2nd, 2017

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, 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.

A final pulse of wind and light snowfall will see wind slabs and cornices continue to grow over Saturday night. The potential for a large wind slab or cornice release to trigger a deeper persistent slab can't be discounted yet.

Confidence

Moderate -

Weather Forecast

Saturday night: Scattered flurries bringing about 5 cm of new snow. Moderate west winds.Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate northwest winds. Freezing level to 1300 metres with alpine temperatures around -8.Monday: A mix of sun and cloud. Light west winds. Freezing level to 1500 metres with alpine temperatures around -6.Tuesday: Cloudy with sunny periods. Light to moderate southeast winds. Freezing level to 1800 metres with alpine temperatures around -4.

Avalanche Summary

Reports from Friday included observations of numerous loose snow releases to Size 1.5 occurring with solar warming near Blue River. Improved visibility also allowed for observations of recent (up to 72 hours old) slab avalanche activity reaching up to Size 4 in the same area. The largest of these avalanches are certain to have failed on deeply buried persistent weak layers.Reports from Thursday included observations of two large (Size 2.5 and Size 3) storm slabs releasing naturally from steep alpine terrain north of Blue River. Crown fractures of these slides ranged from 60-80 cm. Extensive natural sluffing to Size 2 was also observed, with loose dry activity on northerly aspects and loose wet from solar aspects. One Size 1 cornice fall was also reported.

Snowpack Summary

Up to 40 cm of recent storm snow has fallen at upper elevations. The new snow is dry up high and moist at 1800 m and below. This now brings 40-90 cm of accumulated snow which overlies a rain crust below 2000 m or a sun crust on solar aspects at higher elevations. New wind slabs are developing on leeward slopes and behind terrain features and large, fragile cornices exist along ridgelines. At higher elevations, the February weak layers are down 120-150 cm and woke up during last week's storm with many avalanches stepping down to them. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls have also stepped down to these layers last week resulting in some very large full depth avalanches. These layers remain a real concern while more reactive wind slabs and cornices continue to present the risk of acting as triggers for deeper weaknesses.

Problems

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.