Avalanche Forecast

Issued: Mar 18th, 2015 9:37AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is low. Known problems include Storm Slabs and Persistent Slabs.

jlammers, Avalanche Canada

Sea To Sky.

Forecast snowfall amounts are highly uncertain for Thursday. If more than 20cm falls in your area, the Avalanche Danger may be High.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

A pacific storm will intensify on Wednesday night bringing snowfall to the region for Thursday and Friday. A clearing trend is forecast for late Saturday. Up to 25cm of snow is forecast for Wednesday night and Thursday. Around 10-15cm of snow is expected on Friday. 10-15cm is forecast for Saturday. Ridgetop winds should remain strong from the southwest. Freezing levels are expected to hover around 1800m, although Friday may see a spike to about 2200m.

Avalanche Summary

A skier accidentally triggered a size 3 hard wind slab on Monday, which failed on the March crust/facet layer. Skiers also remotely triggered size 1.5-2.5 slabs, most on northerly aspects, some of which failed on the crust/facet layer. A natural and human-triggered cycle of wind slabs was reported on Sunday. A round of storm slab activity is expected over the next few days in response to forecast snow and wind.

Snowpack Summary

Wind slabs (most recently formed with northerly winds, but previously lee to the S-SW) and wind-affected surfaces are the main theme at the snow surface. New snow and wind forecast for Thursday is expected to form new storm slabs. Cornices may also be fragile. A crust/facet persistent weak layer, buried anywhere from 10 to 60 cm down, has started to play up (see avalanche summary). Avalanche problems associated with this layer may linger for a while with the potential for large and destructive avalanches. A deeper crust (formed by heavy rain in February) is down around 70 cm. Below the deeper crust, the snowpack is reported to be generally well-settled and strong. Below treeline, the diminishing snowpack is trending isothermal (same temperature throughout).

Problems

Storm Slabs

Forecast snow and wind will form reactive new storm slabs. Watch for triggering in higher elevation lee terrain.

Be cautious as you transition into wind affected terrain.>Be alert to conditions that change throughout the day.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

In recent days, people have remotely triggered large persistent slab avalanches. The buried crust/facet layer seems variably reactive, and could surprise with nasty consequences.

Choose well supported terrain without convexities.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 5

Valid until: Mar 19th, 2015 2:00PM