Avalanche Forecast

Archived

Dec 22nd, 2019–Dec 23rd, 2019

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

North Columbia.

A big storm recently added a significant load to a buried weak layer. Resist the urge to push into bigger terrain as human triggered avalanches remain likely. Choose conservative terrain and avoid overhead exposure to avalanche terrain.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SUNDAY NIGHT - Cloudy with clear periods and isolated flurries / light northeast wind / alpine low temperature near -7

MONDAY - A mix of sun and cloud / light northwest wind / alpine high temperature near -6

TUESDAY - Mainly cloudy with isolated flurries / southeast wind, 20-40 km/h / alpine high temperature near -10

WEDNESDAY - Cloudy with sunny periods / light northwest wind / alpine high temperature near -12

Avalanche Summary

The likelihood of avalanches will remain elevated on Monday, and avalanches have the potential to be very large.

On Saturday, there were numerous reports of natural, human and explosives triggered avalanches up to size 3.5. A number of these were triggered remotely.

There were numerous reports of natural, human and explosives triggered avalanches up to size 3.5 on Friday.

There were numerous reports on Thursday of natural, explosives and human triggered avalanches up to size 3. Many of these were triggered remotely.

Snowpack Summary

The North Columbias received upwards of 80 cm between Thursday night and Saturday night. Storm slabs are likely widespread and may still be reactive to human triggers.

There is anywhere from 100-160 cm of snow on top of a widespread layer of large, feathery surface hoar crystals. This layer has reportedly been responsible for numerous recent avalanches and may be reactive to human triggers.

A weak layer that formed in late November is now over 170 cm deep. This is the layer of concern relating to the persistent slab avalanche problem. The weak layer may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect.

Terrain and Travel

Make conservative terrain choices and avoid overhead hazard.
Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.
Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.