Avalanche Forecast

Archived

Dec 16th, 2021–Dec 17th, 2021

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

North Columbia.

We are reaching a tipping point where triggering large, destructive avalanches will become more likely . Where exactly these large avalanches can be triggered will be hard to predict. Read the forecaster's blog to learn more.

Confidence

Low - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Thursday night: Some light flurries with light to moderate Northwest winds in the alpine. Low of -15 at 1500m.

Friday: High of -13 at 1500m. Moderate Northwest winds in the morning shifting to Southwest in the afternoon. Sunny and no new snow expected.

Saturday: A storm arrives bringing up to 40cm of new snow with the highest snowfall in the Southwest corner of the forecast region. Winds will be strong from the Southwest. High of -10 at 1500m.

Sunday: High of -9 at 1500m. light snow in the morning. Strong Southwest winds in the morning becoming light West in the afternoon.

Avalanche Summary

One natural size 2.5 was observed in the Monashees on Wednesday on a West aspect at 2150m. This avalanche failed on the early December facet/crust combo. The crown was one meter deep, a good indicator of the high consequences of triggering this layer.

Snowpack Summary

Up to 10cm of low density snow fell over the region Thursday morning. This overlies a variety of surfaces including old wind slab and storm snow.

The defining feature of the snowpack is a widespread crust that reaches as high as 2200 m and now sits 50-100 cm below the surface. In many places overlying snow is well-bonded to the crust but in others weak faceted grains have been observed above it. The facets above the crust are most prominent at treeline where the crust is thinner.

Average snowpack depth at treeline is 250cm.

Terrain and Travel

Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
Be aware of the potential for large avalanches due to the presence of a persistent slab.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.