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Avalanche Forecast

Archived

Jan 12th, 2021–Jan 13th, 2021

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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

With new snow and strong to extreme wind, widespread storm slabs are expected. This new snow will also add load to persistent weak layers in the snowpack. Choose conservative terrain and avoid overhead hazard.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the limited number of field observations.

Weather Forecast

TUESDAY NIGHT - Snow, 10-20 cm / southwest wind, 40-80 km/h / alpine low temperature near -2 / freezing level 2000 m

WEDNESDAY - Flurries, 5-10 cm / southwest wind, 60-80 km/h / alpine high temperature near -2 / freezing level 1500 m

THURSDAY - Mainly sunny / light northwest wind / alpine high temperature near -8 

FRIDAY - A mix of sun and cloud / light to moderate southwest wind / alpine high temperature near -5

Avalanche Summary

Fresh storm slabs are expected to be widespread and easy to trigger. Natural avalanche activity is also possible, and the likelihood of this will increase throughout the day as the new snow piles up.

A large (size three) cornice triggered persistent slab avalanche was reported on a large south-facing alpine slope in the Crowsnest Pass area on Thursday. This avalanche failed on weak facets overlying a hard crust deep in the snowpack and is an example of the "low probability; high consequence" scenario that persistent slab problems often create. View the MIN report HERE.

Snowpack Summary

With 15-30 cm of new snow and strong to extreme southwest wind expected between Tuesday night and Wednesday afternoon, storm slabs are anticipated to be widespread and reactive.

The lower snowpack consists of decomposing crusts and weak, faceted snow. In the Elk Valley, a decomposing surface hoar layer can be found around one of these crusts 60-120 cm below the surface. Avalanche activity on these layers in the lower snowpack has been sporadic, mostly triggered by large loads such as a wind slab avalanche, or a cornice fall. These deeper weak layers are most likely to be human triggered on steep, rocky slopes with a shallow or thin to thick snowpack.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • 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.