Avalanche Forecast

Issued: Mar 30th, 2016 8:59AM

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

triley, Avalanche Canada

Purcells.

Special Public Avalanche Warning for this region. Forecast very warm temperatures, high freezing levels, and strong solar radiation will increase the avalanche danger to HIGH in the alpine during the hottest part of the day.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A well-developed ridge of high pressure will continue to provide clear skies, light winds, and very warm temperatures for Thursday and Friday. Freezing levels may climb as high as 3000 metres, and there may not be a freeze on Friday morning in some areas. A weak trough will move inland from the coast on Saturday, bringing moderate southwest winds and increasing cloud cover. Some light precipitation may make it into the Interior ranges, however it may be mostly rain as the freezing level should remain at about 2500 metres on Saturday.

Avalanche Summary

On Tuesday numerous loose wet avalanches up to size 2.0 were reported, and one of these loose wet slides stepped down to a buried crust down 50 cm and resulted in a size 2.5 on a steep east aspect at 2200 metres. Some natural cornice falls were reported on Monday up to size 2.0. I suspect that avalanche activity will increase as the temperatures and freezing levels rise over the next few days.

Snowpack Summary

Forecast warming and strong solar is expected to result in loose wet avalanches on sun exposed aspects at all elevations. This warming trend may start to affect deeper snowpack layers each day. Surface crusts may break down early, and persistent weak layers may fail if the warming reaches their fragile structure. The late February surface hoar/crust layer is down 40-90 cm. This layer may continue to react to human triggers during periods of strong solar radiation and high daytime temperatures. Loose wet avalanches in motion, or cornice falls may step down to deeply buried weak layers. Cornices continue to be described as large and fragile, and may fail with forecast warming and strong sunshine this week. Conservative terrain without overhead hazard is a good strategy for avoiding the persistent slab problem.

Problems

Persistent Slabs

Continued warm and sunny weather may add enough heat to the snowpack to “wake-up” persistent weak layers buried in the snowpack. Rapid warming of the winter snowpack can result in deeply buried weak layers propagating very large avalanches.

Be aware of the potential for large, deep avalanches due to the presence of a few different persistent weak layers.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Cornices

Continued high freezing levels and very warm daytime temperatures are very likely to result in natural cornice falls. Large cornice falls may trigger buried weak layers resulting in very large avalanches.

Do not travel on slopes that are exposed to cornices overhead.>Cornices become weak with daytime heating, so travel early on exposed slopes.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

3 - 6

Loose Wet

Forecast high freezing levels and very warm daytime temperatures may break down surface crusts early and result in loose wet avalanches from steep solar aspects. Wet slab avalanches are possible if loose snow propagates on a buried crust.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Mar 31st, 2016 2:00PM