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Avalanche Forecast

Archived

Apr 12th, 2021–Apr 13th, 2021

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

Regions

Northwest Inland.

Danger will elevate throughout the day as slopes warm up. Plan your day around avoiding cornices and sun-exposed slopes. Read more in this Forecasters' Blog.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

MONDAY NIGHT: Mostly cloudy skies, 30 km/h southwest wind, freezing level around 1200 m with treeline temperatures around -2 C.

TUESDAY: Mix of sun and cloud, 20 km/h southwest wind, freezing level climbs from 1200 to 1900 m throughout the day, treeline temperatures climb to +1 C.

WEDNESDAY: Sunny, light wind, freezing level climbs from 2000 to 2700 m throughout the day, treeline temperatures climb to +5 C.

THURSDAY: Sunny, light wind, freezing level steady around 2800 m, treeline temperatures around +5 C.

Avalanche Summary

Warm sunny weather this week will likely cause wet loose avalanches on sun-exposed slopes and large cornice falls. After several days of warm weather natural slab avalanches will become a concern.

There were many small (size 1) wet loose avalanches on south-facing slopes at all elevations on Sunday and a few size 2 cornice failures on north and east facing slopes. On Saturday there were a few naturally triggered wind slab avalanches (up to size 2) on northeasterly aspects in the alpine.

Snowpack Summary

Sunny skies and rising freezing levels will result in melting surfaces on solar aspects and lower elevations. 5-20 cm of snow is quickly settling and strengthening, although some wind slabs could linger at upper elevations. The recent snow has covered a variety of snow surfaces, including wind affected snow, crusts on solar aspects and at lower elevations, and soft snow on sheltered slopes at upper elevations.

The lower snowpack is reported as well settled and strong in most areas. However, weak facets exist at the base of the snowpack in the more shallow snowpack zones across the region. Where it exists, this layer has the potential to be triggered on steep, rocky slopes with a shallow or thin to thick snowpack; especially with large loads such as a cornice fall.

Cornices are large, looming, and capable of triggering large avalanches when they fail.

Terrain and Travel

  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Avoid exposure to slopes that have cornices overhead.
  • Recent wind has varied in direction so watch for wind slabs on all 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.

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.

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.