Avalanche Forecast

Archived

Jan 20th, 2023–Jan 21st, 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 new and recent wind slabs in unusual places after rapid shifts between northwest and southwest winds. Surface instabilities aside, the basal snowpack continues to demand thoughtful terrain selection to avoid triggering a very large avalanche. Keep up the safe group management decisions and avoiding shallow rocky start zones.

Confidence

Moderate

Avalanche Summary

Explosives control in the Fernie area yielded storm slabs to size 2 (large) on Thursday, with depths of up to 15 cm and propagations up to 50 m wide. This is a good indication of surface instabilities you may find lingering in in leeward terrain features near ridgecrests on Saturday.

On Tuesday and Wednesday, more human-triggered wind slabs up to size 1 were reported at treeline and above.

Snowpack Summary

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

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

Another crust/facet layer is down 70-150 cm. Below this crust, the basal snowpack is weak and faceted.

Weather Summary

Friday night

Mainly cloudy. Light southwest or northwest winds, more northerly with elevation.

Saturday

Increasing cloud with isolated flurries, increasing overnight. Moderate to strong southwest winds, increasing over the day. Treeline high temperatures around -6.

Sunday

Cloudy with easing flurries and a variable trace to 10 cm of new snow, including overnight amounts. Light to moderate northwest winds. Treeline high temperatures around -6.

Monday

Cloudy with scattered flurries bringing less than 5 cm of new snow. Light to moderate southwest winds. Treeline high temperatures around -6.

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.