Avalanche Forecast

Archived

Dec 4th, 2018–Dec 5th, 2018

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Columbia.

Two buried weak layers in the snowpack appear to be gaining strength, but don't forget about them just yet. Be skeptical of large treeline features, steep south facing slopes and large, rocky alpine bowls.

Confidence

Moderate - Due to the quality of field observations

Weather Forecast

TUESDAY NIGHT - Clear periods / light to moderate northerly winds / alpine temperature near -12WEDNESDAY - Sunny with cloudy periods / light easterly winds / alpine high temperature near -10THURSDAY - Sunny with cloudy periods / light southerly winds / alpine high temperature near -8, low temperature near -11FRIDAY - A mix of sun and cloud / light to moderate southerly winds / alpine high temperature near -6, low temperature near -8

Avalanche Summary

Explosives continue to trigger avalanches to size 1.5 in the region.One size 2 skier triggered avalanche was reported to have run on the surface hoar layer at 2450 m on a northwest aspect on Dec 1Several large, notable avalanches that were reported in the last 10 days in the region are listed below:On December 1 a natural size 3 slab avalanche was seen on Mt. Begbie (east to northeast aspect above 2000 m). It is likely that this avalanche was initiated by a large trigger such as a rock or cornice fall, and that it ran on the October crust.On November 29 an explosives triggered size 2.5 avalanche ran on the October crust on a north to northeast aspect at 2300 m.On November 24 a human triggered size 3 avalanche was reported in the region. This avalanche likely ran on the October crust, as it was reported as a full depth avalanche. Two reports on this avalanche can be found on the Mountain Information Network. MIN

Snowpack Summary

35-65 cm of snow sits on a layer of surface hoar (weak feathery crystals) and sun crust on steeper south facing slopes. The surface hoar is mostly found at treeline, but it may be found in sheltered alpine areas. At the base of the snowpack is a crust that formed near the end of October. This crust is associated with weak, faceted (sugary) snow and has shown some reactivity in the region. This layer is most prominent in the alpine but may exist into upper treeline elevations as well.Snowpack depths taper quickly with elevation, many areas have over 200 cm in the alpine, between 100-170 cm at treeline, and 10-100 cm below treeline.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.