Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Mar 7th, 2023–Mar 8th, 2023

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

Regions

Esplanade, West Purcell.

Cornice failures have the potential to initiate surprisingly large slab avalanches. Steer well clear of overhead hazard and steep solar slopes during periods of strong sun.

Triggering large slab avalanches remains possible in steep, rocky, and wind-affected areas. Sheltered and shaded terrain will offer the best and safest riding.

Confidence

Moderate

Avalanche Summary

With periods of strong sun in the past few days, several large (size 2-3) natural cornice failures have been noted throughout the region. Some of these cornices pulled slabs on the slopes below that failed on persistent weak layers in the mid or lower snowpack. Several large (size 2-3) natural wind slabs failed in south-facing alpine and treeline terrain in Glacier National Park. One large (size 3) natural deep persistent slab was observed in the alpine north of Revelstoke.

Explosive control last weekend produced numerous large persistent and deep persistent slabs up to size 4 on a variety of aspects in the alpine. Several large cornices were also initiated with explosives.

Read more about managing the deep persistent slab problem in our latest Forecaster Blog.

Snowpack Summary

A dusting of new snow overlies a sun crust on steep south-facing aspects, surface hoar in some areas and widespread near surface-faceting from cold temperatures. Last week's 20-60 cm of storm snow has been redistributed by variable winds in exposed areas creating pockets of wind slab that may be found on all aspects.

This recent storm snow overlies a weak layer of faceted snow and a sun crust on sun-affected slopes. This layer has been noted as a failure plane for some recent avalanche activity, as seen in this MIN report from Saturday. A second weak layer in now down 60-110 cm. It is comprised of a sun curst on solar aspects and surface hoar in isolated sheltered and shaded areas. The remainder of the mid-snowpack is generally strong.

The November facets are still prominent at the base of the snowpack. They are showing signs of rounding but there is still a considerable step in resistance between them and the overlying snow. These facets are most pronounced in shallow rocky areas.

Weather Summary

Tuesday night

Clear with cloudy periods. Alpine temperatures reach a low of -9 °C. Ridge wind light from the southeast. Freezing level at valley bottom.

Wednesday

Sunny with cloudy periods. Alpine temperatures reach a high of -6 °C. Ridge wind light from the southeast. Freezing level rises to 800 meters.

Thursday

Sunny with cloudy periods. Alpine temperatures reach a high of -8 °C. Ridge wind light southeast. Freezing level 700 meters.

Friday

A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -8 °C. Ridge wind light from the southeast. Freezing level 600 meters.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.