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Avalanche Forecast

Archived

Mar 30th, 2021–Mar 31st, 2021

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

Regions

Sea To Sky.

Wind slabs could be reactive to skier and rider triggering. 

Rising freezing levels and pockets of sunshine can pack a punch and quickly initiate natural avalanches. Back off slopes before the snow turns moist and avoid overhead hazards like cornices and large avalanche paths.

Confidence

High -

Weather Forecast

A ridge of high pressure will keep the region mostly dry on Wednesday. A frontal wave will bring cloudy skies and light snow amounts by Thursday.

Wednesday: Mix of sun and cloud. Ridgetop wind moderate from the southwest. Alpine temperatures near 0 degrees and freezing levels 1600 m.

Thursday: Cloudy with light snow 2-5 cm. Ridgetop wind strong from the southwest and freezing levels 1200 m. 

Friday: Cloudy with snow amounts 5-10 cm. Ridgetop wind light from the southwest. Alpine temperatures -6 and freezing levels 1000 m.

Avalanche Summary

By midday on Tuesday reports indicated that small loose wet avalanches occurred from steep rocky terrain. Cornices also became weak and failed with daytime warming. No slabs were reported from the slopes below. 

On Sunday, natural storm slab avalanches up to size 2 were reported and numerous size 1.5 slabs were easily triggered by skiers and riders from steep slopes where the new snow sits above a crust. 

The likelihood of triggering avalanches will decrease somewhat in the wake of Sunday's storm, however, human triggering remains likely, especially in wind loaded areas at upper elevations. With so much new snow, even short periods of direct sun can trigger natural avalanches. Cornices are large and should be given a wide berth, especially when the sun comes out.

Snowpack Summary

Up to 40 cm of snow fell throughout the region since the weekend. This was accompanied by strong southwest winds that switched to the northwest. Reactive wind slabs could be lingering on a variety of aspects at upper elevation, especially where they sit above a crust. 

The recent snow sits above a widespread melt-freeze crust, with the exception of high north-facing terrain. It may also be sitting on small surface hoar crystals reported on north and east aspects in the alpine. This recent precipitation likely fell as rain in many areas below treeline. A melt-freeze crust exists below treeline.

Cornices along ridgelines are large, and the likelihood of them failing will increase when the sun comes out.

Terrain and Travel

  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Be aware of highly variable recent wind loading patterns.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.

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.

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.

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.