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 20th, 2012–Mar 21st, 2012

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 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.

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Wednesday: Unsettled conditions with light convective flurries. Freezing level is around 1000m during the day. Winds are light from the S-SE. Thursday: Some uncertainty, but a weak system should give some snow - 5-15cm (greater amounts to the east). Freezing level steady around 1000m. Friday: A drier and sunnier day as a weak ridge builds in. Freezing level rising to 1500m during the day.

Avalanche Summary

We're still seeing almost daily reports of very large avalanches failing on the deeply buried mid-Feb surface hoar layer. The latest report is from the Lumberton snowmobile area in the East Kootenays. A snowmobiler accidentally triggered a very large (Size 3+) avalanche that resulted in a close call. Although triggering the deep persistent weakness is becoming less likely, if you do, the resulting avalanche could have fatal consequences.

Snowpack Summary

An additional 20-30cm of new snow on Tuesday with moderate to strong winds resulted in new wind slab formation in exposed leeward terrain. Several resistant shears have been noted in the storm snow. A sun crust on southern aspects and a spotty 2-6mm surface hoar on north and east aspects is down around 60-100cm. Below that, the more significant early February surface hoar is down 100-180cm. Snowpack tests show moderate to hard forces generating sudden planar shears on this layer. A melt-freeze crust, down 20-30cm, below 1800m provides some bridging to the layers below. Below the early February surface hoar layer, the snowpack is strong in most places. Cornices are very large and would act as a significant trigger for all the layers mentioned above if they drop.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.