Avalanche Forecast

Archived

Jan 21st, 2023–Jan 22nd, 2023

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

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

Lizard-Flathead, South Rockies, Flathead, Lizard, Bull, Elkford East, Elkford West.

Watch for wind slab reactivity as this problem continues to build.

The basal snowpack continues to demand thoughtful terrain selection to avoid triggering a very large avalanche.

Keep up the safe travel choices and avoid shallow rocky start zones.

Confidence

Moderate

Avalanche Summary

Avalanche control with the use of explosives on Thursday, Friday, and Saturday produced several avalanches up to size 2 (large). These were from storm slabs and wind slabs. These instabilities and the deep persistent slab instability should be assumed to exist in the backcountry.

Snowpack Summary

Around 10 cm of recent snow has been redistributed into small wind slabs in exposed areas. It has been blending into older wind-affected surfaces above 1800 to 2000 m and settling on a crust below this elevation.

A crust/facet layer (2 to 15 cm thick at treeline elevation) is down 50 to 90 cm. Where it's thickest, it caps the settled and consolidated mid-snowpack.

Another crust/facet layer is down 70 to 150 cm. Below this crust, the basal snowpack is weak and faceted. The total snowpack depth ranges between 120 and 250 cm.

Weather Summary

Saturday Night

Cloudy, 2 to 5 cm accumulation, 10 to 20 km/h southwest wind gusting to 50, temperature dipping to -8 C.

Sunday

Cloudy, up to 8 cm accumulation with a chance of snow showers, 10 to 15 km/h west winds, temperatures reaching -3 C.

Monday

Cloudy, up to 4 cm accumulation, 15 km/h northwest wind gusting to 35, temperatures -8 to -4 C.

Tuesday

Cloudy with sunny breaks, trace accumulation, 15 km/h southwest wind gusting to 40, temperatures -10 to -5 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Recent wind has varied in direction so watch for wind slabs on all aspects.

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.