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Avalanche Forecast

Archived

Nov 26th, 2020–Nov 27th, 2020

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

Purcells.

 Watch for changing conditions as strong winds may mean that wind slabs become increasingly reactive throughout the day. 

Confidence

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

Weather Forecast

THURSDAY NIGHT - Cloudy with clear periods and isolated flurries / southwest wind, 20-50 km/h / alpine low temperature near -8 

FRIDAY - Mainly cloudy with scattered flurries / southwest wind, 25-50 km/h / alpine high temperature near -4 / freezing level 1000 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 -8 / freezing level 900 m

SUNDAY - A mix of sun and cloud / southwest wind, 15-30 km/h / alpine high temperature near -3  

Avalanche Summary

Strong winds are likely forming fresh wind slabs, which may become more reactive 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 avalanches reported on the early November crust. These have been triggered by both humans and explosives.

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 be forming fresh wind slabs at upper elevations. Expect these wind slabs to be the most reactive in areas that saw more than 10 cm of new snow over the past week. There is a crust from early November that is down approximately 50-75 cm. This layer has been observed to have weak, sugary facets above and below it. Recent observations of this layer indicate that it has the potential to be triggered by humans.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • In times of uncertainty conservative terrain choices are our best defense.

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.