Avalanche Forecast

Archived

Mar 25th, 2013–Mar 26th, 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

Kootenay Boundary.

Confidence

Good

Weather Forecast

A dominating ridge of high pressure will continue over the Interior through the forecast period. Spring-like conditions will remain the theme, with gradual warming Wednesday/Thursday. Tuesday: Mainly clear skies with possible mid-high cloud cover. Freezing levels 1400 m in the afternoon, and then falling back to valley bottom overnight. Ridgetop winds blowing light from the West.Wednesday: Scattered high cloud. Freezing levels 1500 m, and then falling to 800 m overnight. Ridgetop winds light from the South.Thursday: Mostly clear and sunny. Freezing levels 1900 m and then falling to valley bottom overnight. Ridgetop winds will blow light from the SouthWest.

Avalanche Summary

On Sunday, small loose dry/wet avalanches occurred from steeper terrain features. One skier triggered size 1.5 slab avalanche released on a North aspect around 2000 m over a steep convex feature. On Saturday an avalanche fatality occurred in the Hell Roaring riding area located in the eastern ranges of the region. We have very limited information as the investigation is ongoing. At this point it sounds like a size 3 machine triggered slab avalanche. Additionally a skier triggered slab avalanche size 1.5 occurred in the Whitewater area (outside the ski area boundary). This avalanche was triggered from the leeward side of a cross-loaded feature and ran on a buried crust around 1980 m on a North aspect.

Snowpack Summary

20 and 80 cm of last week's storm snow is settling into a cohesive slab overlying a thick crust that exists up to ridge top. The crust appears to have gained some strength in most places, but may still host a poor bond and has been susceptible to skier and rider triggers. A buried surface hoar layer sits approximately 80 cm below the surface and continues to fail in a sudden planar fashion when tested. In some places it may not be a concern due to the thick supportive crust that lies above it. However, it may be more reactive to a trigger from a variable, thin snowpack area or a large trigger like a cornice fall or a snowmobiler.Large fragile cornices loom over many slopes. These may become weak and fail under the influence of the sunshine. Cornice fall can act as a large trigger on slopes below, and may trigger a deeper instability if it exists. Surface snow has become moist, and melt-freeze crusts are forming on solar aspects.

Problems

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.