Avalanche Forecast

Archived

May 15th, 2014–May 16th, 2014

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

Banff Yoho Kootenay.

This is the last regular bulletin. We will update it if there are significant changes. For specific condition information during spring and summer, see Parks Mountain Safety, the Mountain Condition Reports or contact Visitor Safety at 403-762-1470.

Weather Forecast

A light freeze Friday morning, then a mix of sun and cloud with freezing levels up to mountain top by Friday afternoon. Saturday through Monday we expect rain at lower elevations with wet snow in the alpine and precipitation accumulations between 30-45mm. Daytime freezing levels are forecast between 2500m and 3200m with little recovery overnight.

Snowpack Summary

Spring conditions now exist. After cool clear nights a firm melt freeze crust is present which deteriorates with daytime heating. Below 2000m the snowpack is mostly isothermal. Above 2000m the snowpack is generally supportive with the surface becoming moist with daytime heating. Weak basal facets are still present in many locations.

Avalanche Summary

The last week has seen lots of loose wet slides at lower elevations and on steep solar aspects up to size 2.5 with daytime heating. Several cornice failures have also been observed. No recent slab avalanches have been observed however with any sustained warming or major rain events we expect to see increased avalanche activity on the basal facets.

Confidence

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.

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.