Avalanche Forecast

Issued: Apr 13th, 2016 9:29AM

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

jsmith, Avalanche Canada

Sea To Sky.

Spring conditions with a brief return to winter in the alpine. Expect to find touchy wind slabs sitting on slippery crusts.

Summary

Weather Forecast

THURSDAY: Freezing level: 2000m, mostly sunny, light variable ridgetop winds. FRIDAY: Freezing level: 1700m, mostly sunny, light southerly ridgetop winds. SATURDAY: Freezing level: 2300m, mix of sun and cloud, light southerly ridgetop winds.

Avalanche Summary

On Tuesday, explosive control work near Whistler produced several size 2 cornice triggered avalanches. With the new snow and wind I would expect fresh wind slabs to be ripe for human triggers on Thursday.

Snowpack Summary

Cornices are large, fragile, and could trigger deep slab avalanches that run to valley bottoms. 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. 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, especially on steep, rocky faces.

Problems

Wind Slabs

Be on the look out for fresh touchy wind slabs sitting on slippery crusts in the alpine.

Be cautious as you transition into high elevation wind affected terrain. >Travel on ridgetops to avoid wind slabs on slopes below. >

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

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.

Give cornices a wide berth when traveling on or below ridges. >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, South West.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

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.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. > Look for signs of surface instabilities such as pinwheeling and point releasing near cliffs. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Apr 14th, 2016 2:00PM