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

Jan 18th, 2023–Jan 19th, 2023

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

Regions

Kootenay Boundary, Bonnington, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir.

A reactive weak layer is producing large human-triggered slab avalanches. The problem is especially prevalent at mid-elevations. With a complex snowpack, terrain choices and good group management techniques are key. Regroup in safe locations, space out, and avoid rocky, thin-to-thick snowpack areas.

Confidence

Moderate

Avalanche Summary

On Tuesday, improved weather allowed for better visibility noting the widespread natural avalanche activity that occurred last weekend. Most of these avalanches reportedly failed on the surface hoar interface buried early January. Explosive control results included large deep persistent slab avalanches up to size 3 and storm slabs to size 2. Human triggering and remote triggering remain possible, especially 1700-2100 m being the critical elevation band and east-to-northeast aspects on the buried surface hoar layer.

Snowpack Summary

Upper elevations have received 20-35 cm of new snow over the past week. It overlies a mix of wind-affected and sheltered low-density storm snow above about 1700 m and a rain crust at lower elevations.

At higher elevations, 40 to 60 cm of snow now sits on a layer of surface hoar that was primarily preserved in sheltered terrain at treeline. It has been identified as the failure plane in many recent avalanches in the region.

A facet/crust layer is down 40-90 cm (and 2-10 cm thick at TL elevation). Below this, the mid-pack is settled and consolidated.

A concerning and weak layer of facets and crust 20-50 cm thick make up the basal snowpack.

Weather Summary

Wednesday Night:New snow 5-10 cm overnight. Steady ridgetop winds from the southwest. Alpine temperatures near -7 C and freezing levels valley bottom.

Thursday: Mainly cloudy with sunny breaks and isolated flurries. Alpine temperatures reach a high of -7 C. Ridgetop wind light from the northwest. Freezing level rises to 1000 metres.

Friday

A mix of sun and cloud. Alpine temperatures reach a high of -4 C. Ridge wind light from the northwest. Freezing level near 1000 m.

Saturday

Sunny. Alpine temperatures reach a high of -5 C. Ridge wind mostly light with moderate to strong gusts from the northwest. Freezing level rises to 800 metres.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • Uncertainty is best managed through conservative terrain choices at this time.

Problems

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.

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.