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Avalanche Forecast

Archived

Apr 6th, 2021–Apr 7th, 2021

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

Regions

Purcells.

Minimize exposure to large looming cornices weakening with daytime warming and solar radiation. Cornice fall could trigger a slab on the slope below.

Isolated pockets of wind slab may be found in immediate leeward features in the alpine.

Confidence

High -

Weather Forecast

Tuesday Night: Clear. Ridgetop wind light to moderate from the South and freezing levels 1200 m. 

Wednesday: Mix of sun and cloud with light snow 5 cm. Ridgetop wind moderate from the southwest. Alpine temperatures near -4 and freezing levels 1700 m. 

Thursday: Mix of sun and cloud with flurries. Ridgetop wind moderate from the West. Alpine temperatures near -7 and freezing levels 1400 m.

Friday: Cloudy. Ridgetop wind moderate to strong from the South. Alpine temperatures near -5 and freezing levels 1600 m.

Avalanche Summary

On Tuesday, wet loose pinwheels were reported from steep solar aspects.

On Monday, several wet loose natural avalanches were reported up to size 2 on solar slopes. Cornices have been reactive in the last few days both to explosives and naturally, occasionally triggering wind slabs on slopes below. 

The weather pattern is spring-like and fairly benign. Get after it early before daytime warming kicks in and solar radiation weakens the snowpack and cornices. 

Remember to stay well back from ridgetops that might be corniced and to avoid slopes with overhead cornice exposure especially under the current conditions where recent rapid growth and daytime warming has made them large and fragile. 

Snowpack Summary

The convective nature of Sunday's storm resulted in greatly variable snowfall amounts through the region, as much as 50 cm around Golden and 5-20 cm elsewhere. The recent snow was accompanied by strong southwest wind and may have formed isolated pockets of wind slab on leeward slopes at upper elevations. Reports indicate that the new snow is bonding well to underlying surfaces which include wind-affected snow in the alpine or crust on solar aspects and below 1900 m. Below this elevation and on solar aspects the new snow dusts crusty surfaces down to 1500 m. Below 1500 m, the moist snowpack is quickly diminishing.

A widespread crust layer from the mid-March warm spell can be found 30-60 cm deep, and a small surface hoar and facets have been observed at this depth on some isolated north-facing slopes. Reports suggest the snow is generally well bonded to these layers but isolated instances of large solar-triggered slab avalanches running on the crust have been observed. Deeper layers are strong and have been unreactive over the past few weeks.

Terrain and Travel

  • Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
  • Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Carefully evaluate bigger terrain features on an individual basis before committing to them.

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.