Avalanche Forecast

Archived

Feb 20th, 2024–Feb 21st, 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.

A deep persistent slab problem remains where the near-surface crust is thin or absent.

Low-probability, high-consequence problems are best managed with conservative terrain choices.

Confidence

Moderate

Avalanche Summary

On Monday, natural loose dry avalanches were reported to size 1 in steep polar aspects.

Over the weekend, several wind slab and loose avalanches were reported, up to size 1.5, in steep alpine terrain, some triggered by humans, and some by the sun.

Snowpack Summary

1 to 5 cm of snow overlies wind affected surfaces in open areas and a sun crust on solar slopes.

In sheltered areas, 10 to 30 cm of settling snow sits over a frozen crust that formed in early February. This crust is generally supportive to the weight of a human below treeline, but becomes breakable around treeline, and disappears as you ascend higher into the alpine.

The midpack is generally faceted.

The bottom 15-30 cm of the snowpack consists of weak faceted grains, depth hoar, and crusts that continue to produce sporadic, large avalanches.

Weather Summary

Tuesday Night

Mostly cloudy. 0 to 5 cm of snow. 10 to 25 km/h southwest ridgetop wind. Treeline temperature around -3 °C. Freezing level rising to 1200 m.

Wednesday

Partly cloudy. 0 to 2 cm of snow. 10 to 20 km/h southwest ridgetop wind. Treeline temperature around -2 °C. Freezing level rising to 1700 m.

Thursday

A mix of sun and cloud. 20 to 30 km/h southwest ridgetop wind. Treeline temperature around -1 °C. Freezing level rising to 1700 m.

Friday

A mix of sun and cloud. 10 to 25 km/h west ridgetop wind. Treeline temperature around 0°C. Freezing level rising to 1900 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Conditions may have improved, but be mindful that deep instabilities are still present.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
Recent wind has varied in direction so watch for wind slabs on all aspects.

Problems

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.

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.