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 20th, 2023–Jan 21st, 2023

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 possible, human triggered probable.
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

Kootenay Boundary, Bonnington, Kootenay Pass, Norns, Rossland, South Okanagan, Ymir, Moyie, St. Mary.

A lull in avalanche activity Thursday says more about savvy backcountry use than it does about drastic changes in our problematic snowpack. A local guide put it well: choosing "fat snowpack, low angle" lines is the strategy to employ. We need more than a subtle change!

Confidence

Moderate

Avalanche Summary

Aside from thin surface sluffs running on Wednesday's rime crust, no new avalanches were observed on Thursday.

Reports continue to show a general quieting down of avalanche activity on persistent weak layers, with a few notable occurrences, like an anomalous natural size 2 on Wednesday near Ymir peak that may have failed on the early January surface hoar, considering its distance from the natural cycle on the weekend. A vehicle in the southern Valhallas triggered a size 1.5 on this layer on Wednesday as well.

On Tuesday, improved weather allowed for better visibility noting the widespread natural avalanche activity that occurred last weekend. Many of these avalanches failed on the early January surface hoar.

Explosive control results since this cycle have included large deep persistent slab avalanches up to size 3 and storm slabs to size 2.

Human triggering and remote triggering the layers responsible for these avalanches remains possible, with 1700-2100 m and east-to-northeast aspects being the critical elevation and aspect ranges for the early January layer.

Snowpack Summary

In exposed areas, northerly winds have been redistributing 10-15 cm of new snow, likely creating small wind slabs in a reverse loading pattern. In many areas the new snow accumulated on a thin rime or freezing rain crust that formed in the region on Jan 18, a new layer for us to watch over the near term.

Including the new snow, about 30-40 cm has been settling and bonding to an older mix of wind-affected and sheltered lower density storm snow above about 1700 m and to a rain crust from mid January at lower elevations.

A more problematic layer of weak surface hoar from early January now sits preserved 50 to 70 cm deep, especially prevalent in sheltered terrain at treeline. This layer has been identified as the failure plane in many recent avalanches in the region and remains reactive in snowpack tests.

Another problematic layer composed of a facet/crust combination is down 60-90 cm (and 2-10 cm thick at treeline 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.

Check out an awesome state of the snowpack video update HERE.

Weather Summary

Friday night

Increasing cloud. Light to moderate northwest winds, easing and shifting southwest.

Saturday

Becoming cloudy with a short period of snowfall at the end of the day bringing up to about 5 cm of new snow or just over, mostly in the evening. Moderate to strong southwest winds, increasing over the day. Treeline high temperatures around -5

Sunday

Becoming sunny. Moderate to strong northwest winds easing over the day. Treeline high temperatures around -4.

Monday

Mainly cloudy with isolated flurries in the afternoon. Light variable winds, mainly westerly, increasing over the day and overnight. Treeline high temperatures around -6.

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.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

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.

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.