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Avalanche Forecast

Archived

Feb 22nd, 2024–Feb 23rd, 2024

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

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Before committing to a slope, carefully assess steep, rocky, and wind-affected areas where triggering slabs is more likely.

Confidence

Moderate

Avalanche Summary

On Wednesday a large (size 2) slab was triggered by sluffing from overhead rocky terrain. Another smaller (size 1.5) naturally occurring wind slab and some loose wet avalanches were also reported.

On Tuesday, a large (size 2) cornice fall and a small (size 1) skier-controlled wind slab avalanche were reported.

Snowpack Summary

5 to 10 cm of snow recently fell across the region. At upper elevations near ridgetops, this new snow may have formed wind slabs on lee north and east facing slopes. Steep south and west facing slopes have a sun crust.

In sheltered areas, this new snow may overlie a weak layer of surface hoar. Below this, 10 to 30 cm of settling snow sits over a frozen crust. This crust disappears gradually as you ascend into the upper alpine.

The midpack is generally faceted.

The bottom 15 to 30 cm of the snowpack consists of a deep persistent weak layer of facets, depth hoar, and crusts that have the potential to produce sporadic, large avalanches.

Weather Summary

Thursday Night

Mostly cloudy, no new snow, 15 to 25 km/h west ridgetop wind, treeline temperature around -9 °C, freezing level dropping to the valley bottom.

Friday

A mix of sun and cloud with no new snow, 10 to 20 km/h southwest ridgetop wind, treeline temperature around -1 °C, freezing level rising to 1500 m.

Saturday

Cloudy with 1 to 2 cm of snow, 25 km/h west ridgetop wind, treeline temperature around 0 °C, freezing level rising to 1600 m.

Sunday

Cloudy with 1 to 6 cm of snow, 25 - 40 km/h southwest ridgetop wind, treeline temperature around 0 °C, freezing level rising to 1700 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger 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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.