Avalanche Forecast

Issued: Apr 19th, 2016 9:26AM

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.

jsmith, Avalanche Canada

Kootenay Boundary.

Spring Conditions. Record setting temperatures and ongoing sunny weather will increase the likelihood of large destructive wet slab avalanches, especially if there is little or no overnight refreeze of the snow surface.

Summary

Weather Forecast

WEDNESDAY: Freezing Level: 3700m, sunny, light southerly ridgetop winds. THURSDAY: Freezing Level: 3500m, sunny in the morning, then increasing cloud in the late afternoon, light southerly ridgetop winds. FRIDAY: Freezing Level: 3300m, mix of sun and cloud, light southerly ridgetop winds.

Avalanche Summary

Most commercial operations have closed for the season, and data is becoming sparse. However, with the extremely high freezing levels, sunny skies, 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. The snowpack in many areas has 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

Extremely high freezing levels and little to no overnight surface freeze will increase the potential for sporadic deep wet slab release.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 6

Cornices

If the sun is shining, cornices present a significant hazard. Even if they don't trigger a slab avalanche when they fall onto a slope, they have a nasty habit of running surprisingly long distances.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Loose Wet

Solar radiation in the spring can rapidly change the hazard from low to high. Plan ahead and monitor the effect of solar radiation carefully.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Apr 20th, 2016 2:00PM