Avalanche Forecast

Archived

Dec 17th, 2021–Dec 18th, 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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

North Columbia.

Avoid "thick to thin" areas and steep roll overs, Especially in treeline terrain. Persistent slabs are challenging to manage, if in doubt choose conservative terrain. If you observe more than 30cm of new snow consider the hazard rating to be high in the treeline and alpine.

Confidence

Moderate -

Weather Forecast

Friday: Low of -17 at 1500m. No new snow expected and moderate Southwest winds.

Saturday: A storm arrives bringing 15 to 30cm 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 -11 at 1500m. light snow in the morning. Strong Southwest winds in the morning becoming light in the afternoon.

Monday: No new snow expected. Moderate wind from the Southwest and a high of -16 at 1500m.

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

The incoming weather will form new wind slab in the alpine and treeline.

The defining feature of the snowpack is a widespread crust that reaches as high as 2200m and now sits 60-120 cm below the surface. In some 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. We expect the incoming weather to increase the likelihood of triggering this layer.

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.