Archived

Avalanche Forecast

Nov 20th, 2011–Nov 21st, 2011

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

4: High

The avalanche danger rating at treeline will be high

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

4: High

The avalanche danger rating at treeline will be high

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Sea To Sky.

This bulletin is based on limited data. Local variation in conditions and danger levels are likely to exist. To produce more accurate forecasts, we need information. Please send an email to forecaster@avalanche.ca.

Confidence

Poor - Due to limited field observations

Weather Forecast

Monday: The storm begins. Expect snowfall to increase throughout the day and winds to turn southwest. Freezing levels could reach 1500m, Tuesday: Snow, at times heavy. Continued strong southwest winds and freezing levels peaking at 1700m. Wednesday: Snow tapering through the day, with a bit of a lull late in the day. Southwest winds continue with freezing levels reaching 1200m.I would not be surprised with 80-100cm of new snow within the forecast period.

Avalanche Summary

Avalanche activity has slowed down with the colder temperatures, but recent reports include wind slab avalanches up to Size 2.5 failing on the crust/surface hoar combo that was buried November 9. Some slabs were up to a metre deep and pulled back into low angled terrain on ridges showing incredible propensity for propagation. The critical elevation band for the crust/surface hoar combo is between 1800 and 2050m.

Snowpack Summary

There has been limited new snow in the past couple of days and the colder temperatures have tightened up the storm snow instabilities. The snowpack sits at about 100cm in sheltered locations at treeline, with deeper, wind deposited pockets in the alpine and around ridgeline features. A rain crust, buried November 9 is prominent between 1800m and 2050m and has surface hoar crystals either above, within or slightly below it. This crust/surface hoar combo is buried 40 to 70cm and is the deeper layer of concern.

Avalanche Problems

Wind Slabs

Near ridgecrests and terrain breaks, and in cross-loaded gullies.

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

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 4

Persistent Slabs

Between 1800-2050m there is a rain crust that provides a consistent sliding layer. The chance of triggering this deeper layer from a smaller, storm related avalanche is high.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 5

Storm Slabs

As the storm intensifies storm slabs will become cause for concern. Be cautious in areas with more than 30cm new snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 3