Avalanche Forecast

Archived

Jan 19th, 2024–Jan 20th, 2024

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

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 possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Fresh wind slabs at higher elevations can be found on all aspects. Expect as temperatures warm, that human triggered avalanches will become likely.

Confidence

Moderate

Avalanche Summary

On Thursday explosive avalanche control missions triggered a very large avalanche size 3.5. This avalanche failed on the deep persistent slab layer and was 100 to 250 cm in slab depth, running over 500 meters in length. Earlier in the week natural and explosives triggered wind slab and loose dry avalanches were reported to size 1 and 1.5.

If you go out in the backcountry, please consider sharing your observations on the Mountain Information Network (MIN).

Snowpack Summary

5-10 cm of low density new snow is sitting on weak faceted snow in many areas. In exposed terrain at treeline and above, this new snow is now obscuring old wind slabs.

The mid and lower snowpack is generally weak with several layers of note. Of greatest concern are weak facets and/or depth hoar located at the bottom of the snowpack, particularly in alpine terrain.

Snowpack depths at treeline range from 70 to 160 cm.

Weather Summary

Friday Night

Mainly cloudy with isolated flurries, 1-2 cm of snow, southwest ridgetop wind 10 to 30 km/h, treeline temperature -14 °C.

Saturday

Mainly cloudy with isolated flurries, 1-2 cm of snow, west ridgetop wind 20 to 40 km/h, treeline temperature -15 °C.

Sunday

Mainly cloudy with flurries, 2-4 cm of snow, southwest ridgetop wind 10 to 30 km/h, treeline temperature -10 °C.

Monday

Mainly cloudy with flurries, 2-4 cm of snow, southwest ridgetop wind 10 to 30 km/h, treeline temperature -8 °C.

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.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.

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.