Regions
Banff Yoho Kootenay.
With rising temperatures and forecasted snow expect the danger level to increase. Conservative route choices are in order.
Weather Forecast
A low pressure system will track across the south part of BC bringing rising freezing levels, significant snow-fall , and strong south and sw winds. Freezing levels rising to 1500 m in Lake Louise on Thursday. 20-30 cm of snow are forecasted to fall by Friday. The avalanche danger will increase through the end of the week.
Snowpack Summary
10-30 cm of recent storm snow overrides a mid pack that is largely weak and facetted. Moderate southerly winds will have created some soft slabs in alpine lee features.
Avalanche Summary
Explosive control on Tuesday produced small results up to size 2 across the forecast region. On Wednesday morning a natural Class 3.5-4 avalanche was triggered on the Mt Stephen Road Avalanche Path. This was triggered at 2600m by a large serac fall and ran down to the bottom of the run-out. Debris on highway was 50m wide X 1.5m deep.
Problems
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.