Avalanche Forecast

Issued: Mar 31st, 2016 9:27AM

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

jfloyer, Avalanche Canada

Purcells.

Special Public Avalanche Warning for this region. Continued very warm temperatures with little overnight freeze coupled with strong solar radiation will increase the avalanche danger to HIGH in the alpine during the hottest part of the day.

Summary

Confidence

High

Weather Forecast

A high pressure ridge continues to bring warm, sunny weather to this region. Freezing levels are expected to remain as high as 3000 m through Friday. On Saturday, some clouds move in, we should see a slight lowering of the freezing level to around 2500 m. Winds are forecast to increase to around 30 km/h from the southeast. On Sunday, expect a mix of sun and cloud and freezing levels around 2300 m.

Avalanche Summary

On Wednesday, slab and loose snow avalanches were reported up to size 2 on a variety of aspects, mostly triggered by cornices or solar radiation. 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.

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

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.

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

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

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

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Valid until: Apr 1st, 2016 2:00PM