Avalanche Forecast

Archived

Nov 28th, 2020–Nov 29th, 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.

Recent strong southwest winds have created fresh wind slabs on lee features at treeline and above. These wind slabs may be surprisingly reactive in areas where they are sitting on a spotty layer of small surface hoar.

Confidence

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

Weather Forecast

SATURDAY NIGHT: Clear / Light, west wind / alpine low temperature -13 / Freezing level valley bottom.

SUNDAY: Mostly sunny / Light, west wind / alpine high temperature -6 / Freezing level valley bottom.

MONDAY: Cloudy with flurries; 0-3 cm. / Light to moderate, west wind / alpine high temperature -7 / Freezing level valley bottom.

TUESDAY: Mostly sunny / Light, west wind / alpine high temperature -9 / Freezing level valley bottom.

Avalanche Summary

Check out this notable skier triggered avalanche from Quartz Creek on Thursday. The recently buried layer of small surface hoar that caused this avalanche could likely catch riders by surprise this weekend!

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

Recent strong southwest winds have created fresh wind slabs on lee features at treeline and above. There have been a couple human triggered avalanches on a recently buried layer of small surface hoar. This layer has been reported as "spotty" and is most likely to be present in sheltered areas. 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 and is most likely to be reactive to human triggers on south facing slopes and in shallow, rocky, snowpack areas in the alpine.

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.
Closely monitor how the new snow is bonding to the old surface.
Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.