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Avalanche Forecast

Archived

Mar 7th, 2021–Mar 8th, 2021

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 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

Sea To Sky.

Sunny skies and rising temperatures may initiate wet loose activity on lower elevation and/or sun-exposed slopes. Steer clear of cornices and wind-drifted areas as they have the potential to produce large avalanches. 

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

Dry conditions for the next few days

Sunday night: Mostly cloudy, scattered flurries with up to 5 cm of snow, light southeast wind, freezing level dropping to valley bottom. 

Monday: Mainly sunny, light east wind, freezing level rising to 1400 m and dropping to valley bottom overnight.

Tuesday: Mix of sun and cloud, light variable wind, freezing level rising to 1400 m and dropping to valley bottom overnight.

Wednesday: Sunny, light north wind, freezing level rising to 1400 m and dropping to valley bottom overnight.

Avalanche Summary

Explosive mitigation on Saturday produced numerous large cornice and storm slab avalanches, with 50-100 cm crown depths. Explosives also released a very large (size 3) wind slab avalanche on a northeast aspect above 2000 m. 

Reports indicate that a natural avalanche cycle occurred during the storm on Friday, with small to large (size 1-2.5) avalanches releasing in the storm snow across aspects and elevations. See this MIN report for an example from Hanging Lake.

Snowpack Summary

50-100 cm of snow accumulated over the weekend, and it is settling rapidly. The recent snowfall was accompanied by strong south winds, forming wind slabs on leeward slopes that may be likely to trigger. Massive cornices exist on ridgelines, which can act as triggers on slopes below. Rising temperatures and strong sun on Monday is expected to destabilize cornices and recent snow. Watch for signs that the snow is rapidly warming, such as pinwheels, rollerballs, and point releases.

In isolated areas with a shallower snowpack in the region, a layer of facets, spotty surface hoar, and/or crusts buried in mid-February may still be preserved. There have been no avalanches reported on this layer; however, large triggers, such as an avalanche in motion, cornice fall have the potential to trigger this deeper layer in areas where it may still exist.

The mid and lower snowpack is well settled and strong in most areas.

Terrain and Travel

  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Cornice failure may trigger large avalanches.
  • As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.

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.

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.