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Avalanche Forecast

Archived

Jan 13th, 2021–Jan 14th, 2021

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

Regions

South Rockies.

Recent heavy snowfall means that storm slabs will be widespread and easy to trigger. Don't let the nicer weather lure you into bigger terrain.

Be aware of the potential for solar triggered avalanches. With so much new snow, it may not take much sun to trigger avalanches.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

WEDNESDAY NIGHT - Cloudy with clear periods / moderate northwest wind / alpine low temperature near -12

THURSDAY - Mainly sunny / moderate northwest wind / alpine high temperature near -5 

FRIDAY - A mix of sun and cloud / moderate to strong west wind / alpine high temperature near -2 / alpine temperature inversion / freezing level 1500 m

SATURDAY - A mix of sun and cloud / moderate southwest wind / alpine high temperature near -6

Avalanche Summary

With a lot of new snow and recent strong to extreme winds, storm slab avalanches will probably be easy to trigger on Thursday, especially in wind loaded areas, and on sun-exposed slopes.

It is very likely that a natural avalanche cycle occurred on Tuesday night and into Wednesday during the storm.

A large (size three) cornice triggered persistent slab avalanche was reported on a large south-facing alpine slope in the Crowsnest Pass area last 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

The region received 15-30 cm of new snow between Tuesday night and Wednesday, with strong to extreme westerly winds. Storm and wind slabs are likely 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

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Avoid freshly wind loaded terrain features.
  • 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.