Avalanche Forecast

Archived

Apr 22nd, 2012–Apr 23rd, 2012

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

South Columbia.

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Broken cloud is forecast for Monday with the possibility of light rain in the afternoon, particularly in the north of the region. Ridgetop winds are expected to be moderate from the southwest with freezing levels sitting at about 3000m.

Avalanche Summary

Widespread wet snow avalanches to size 2 were reported from the region over the weekend. Large cornice fall at 2400m was also reported releasing a size 2 slab. Continued wet avalanche activity is expected on Monday with forecast high freezing levels.

Snowpack Summary

On Thursday night, light to locally moderate amounts of snow fell forming wind slabs that have settled considerably or turned to wet slabs with warming over the weekend. The recently fallen snow overlies melt-freeze crust sandwiches and wet grains at treeline and in the alpine while warm temperatures continue to penetrate and weaken the isothermal snowpack at lower elevations. The mid-February buried surface hoar layer is down about 140-220 cm. The likelihood of avalanches failing on this layer has been very low due to cooler temperatures, however it may wake up with warming and the consequence continues to be very large destructive avalanches. Cornices in the region are very large and have may become weak with spring temperatures.

Problems

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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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.