Avalanche Forecast

Issued: Apr 20th, 2016 8:56AM

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

triley, Avalanche Canada

South Rockies.

Spring Conditions. Record breaking warm weather continues. Expect the likelihood of wet slab avalanches, cornice falls, and loose wet avalanches to increase during the heat of the day.

Summary

Weather Forecast

Clear overnight with light winds and freezing levels down to 2000 metres. Clear and sunny on Thursday with light winds and freezing levels rising up to at least 3500 metres. Mix of sun and cloud on Friday with some convective showers/flurries and a chance of thunderstorms. Freezing level down to about 2000 metres on Saturday with convective showers/flurries.

Avalanche Summary

No new avalanches reported in this region. Most commercial operations have closed for the season, and data is becoming sparse. However, with the forecasted warm up and lack of overnight surface freezing, I would expect cornice failures and sporadic large wet slab avalanches.

Snowpack Summary

Monitoring the overnight freeze of the snow surface is very important during the spring. If the snow surface does not freeze overnight or if the crust is only a few cm thick, the effect of daytime heating and solar radiation will weaken the snowpack much more quickly than it would if there is a well frozen thick crust. This is because the crust must first melt before the sun can weaken the snowpack. Deeply buried weak layers in the mid snowpack and near the ground still have the potential to wake up and become active with a rapid warm up. While unlikely, releases on these deeply buried weak layers would result in very large avalanches. Glide cracks are widespread, active, and best avoided. Cornices are large, fragile, and could trigger deep slab avalanches that run to valley bottoms. Low elevation and thin snowpack areas have become isothermal, meaning the snowpack is 0 degrees Celsius throughout. An isothermal snowpack is more prone to full depth wet slab avalanches during the heat of the day.

Problems

Wet Slabs

The likelihood of wet slab avalanches will increase with forecast high freezing levels and strong solar radiation. Areas that do not re-freeze overnight may become very weak early in the day.

Avoid slopes with glide cracks. >Be aware of the potential for large, deep avalanches. >Travel early before the heat of the day, and avoid big slopes in the afternoon. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Cornices

Strong solar radiation and little or no overnight freeze will continue to weaken cornices. Avoid travel beneath cornices.

Pay attention to overhead hazards like cornices. >Cornices become weak with daytime heating, so travel early on exposed slopes. >Cornice releases have the potential to trigger deeply buried weak layers. >

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Loose Wet

Sunny skies and high freezing levels will weaken the surface snow on solar aspects. Shaded aspects in the alpine may warm up enough to release as loose wet avalanches.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. >Watch for surface clues such as sluffing off of cliffs and pinwheeling. These are red flags that should prompt you to reevaluate the conditions. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Apr 21st, 2016 2:00PM