Avalanche Forecast

Issued: Apr 2nd, 2017 3:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs, Cornices and Loose Wet.

rbuhler, Avalanche Canada

Kootenay Boundary.

The recent storm snow is expected to remain reactive to triggering in high north facing terrain. Extra caution is needed around all steep sun exposed slopes as well any slopes exposed to large cornices.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Mostly sunny conditions are expected on Monday with light alpine wind from the north. Freezing levels are forecast to drop to valley bottom Sunday overnight and reach around 1700 m on Monday afternoon. A mix of sun and cloud is expected on Tuesday with light alpine wind from the southwest and freezing levels reaching around 1800 m in the afternoon. A mix of sun and cloud is forecast for Wednesday with moderate alpine wind and freezing levels reaching 2400 m in the afternoon.

Avalanche Summary

On Saturday, isolated natural storm slab avalanches were reported with thickness of 20 cm. Natural sluffing was also reported on all aspects. On Friday, a natural size 2 storm slab avalanche was observed on a southeast aspect at 2250 m. A natural size 2.5 persistent slab was reported on west and northwest aspects at 2300 m and was 60-80 cm deep. Solar triggered loose wet avalanches up to size 2.5 were also observed throughout the region. A skier triggered a size 2 cornice on a northeast aspect which triggered a soft slab on the slope below. On Monday, the sun is expected to destabilize the upper snowpack and extra caution is required when/if the surface crust breaks down. Natural solar triggered sluffing should be expected from steep slopes as well as natural cornice releases on all aspects. In high elevation shaded terrain, the recent storm snow is expected to remain reactive to human triggering, especially in wind loaded terrain.

Snowpack Summary

The region is expected to be entering a period of widespread melt-freeze conditions on all aspects and elevations except for high north facing terrain where the surface snow is expected to remain dry. In high elevation shaded terrain, incremental loading over the past week has formed storm slabs. At lower elevations and on sun exposed slopes, there are likely several crust layers in the upper snowpack. A rain crust which was buried on March 21 and extends into the alpine is now down 60-80 cm. This crust was recently reactive to heavy triggers and several avalanches released on it during the solar cycle last week. At elevations above around 2100m, the February persistent weak layers may still be lingering down around 100-150cm and weak basal facets may still be lingering in shallow snowpack areas. These layers appear to have gone dormant but isolated avalanches could still have the potential to step down in the right conditions.

Problems

Storm Slabs

The recent storm snow is expected to remain reactive on Monday, especially in wind loaded terrain on high northerly aspects. On solar aspects, the sun may trigger moist/wet slab avalanches.

Use ridges or ribs to avoid pockets of wind loaded snow.Use caution on steep open slopes and unsupported convex rollsBe alert to conditions that change with elevation.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Cornices

Large cornices are expected to become weak with daytime warming or sustained sun exposure. A large cornice release has the potential to trigger a deeply buried weak layer in the snowpack.

Pay attention to overhead hazards like cornices which could trigger a deep persistent slab.Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.Give cornices a wide berth when travelling on or below ridges.

Aspects: North, North East, East, South East.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 3

Loose Wet

Solar triggered loose wet avalanches are expected from steep sun exposed slopes during the heat of the day.

Be cautious of sluffing in steep terrain.Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Apr 3rd, 2017 2:00PM