Avalanche Forecast

Archived

Nov 26th, 2020–Nov 27th, 2020

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

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.

Watch for changing conditions as strong winds may mean that wind slabs become increasingly reactive throughout the day. Avoid overhead hazard during times of rapid loading due to strong winds.

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

THURSDAY NIGHT - Cloudy with clear periods and isolated flurries, up to 5 cm / southwest wind, 20-50 km/h / alpine low temperature near -6 / freezing level 900 m

FRIDAY - Mainly cloudy with scattered flurries, up to 5 cm / southwest wind, 25-50 km/h / alpine high temperature near -4 / freezing level 1100 m

SATURDAY - A mix of sun and cloud with isolated flurries / west wind, 20-40 km/h, easing in the afternoon / alpine high temperature near -6 / freezing level 900 m

SUNDAY - A mix of sun and cloud / south wind, 20-30 km/h / alpine high temperature near -3

Avalanche Summary

Strong winds, recent storm snow, and warming temperatures will likely promote fresh wind slab formation. These slabs may become easier to trigger throughout the day.

There have been very few reports of avalanches in the region, however observations are limited at this time.

In the past week there have been a few size 2-3 avalanches reported on the early November crust in both the South Columbia and neighbouring Glacier National Park region.

If you get out into the mountains, please consider sharing your observations on the Mountain Information Network!

Snowpack Summary

Strong winds on Thursday night and Friday will likely form fresh wind slabs at upper elevations. There are a couple of crusts in the mid snowpack, from mid and early November. The most prominent of these is from early November, and it has been reported that there are weak, sugary facets above and below this crust. It is down approximately 70-100 cm, and recent observations indicate that this layer has the potential to be triggered by humans. Several reports indicate that it is likely the most reactive on south facing slopes.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

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.

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.