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Avalanche Forecast

Archived

Jan 15th, 2021–Jan 16th, 2021

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

South Rockies.

There have been a few large persistent slab avalanches recently. These are difficult to predict, so conservative terrain selection is the best management strategy. Look for low-angle, sheltered slopes for the best snow, and the safest riding.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

FRIDAY NIGHT - Cloudy with clear periods / moderate to strong northwest wind / alpine low temperature near -10

SATURDAY - Cloudy with sunny periods / moderate to strong northwest wind / alpine high temperature near -9 

SUNDAY - Cloudy with sunny periods / strong west wind / alpine high temperature near -6 

MONDAY - Mainly sunny / light to moderate northwest wind / alpine high temperature near -7

Avalanche Summary

There was one explosives triggered size 2.5 wind slab avalanche, and one natrual size 3 persistent slab avalanche reported in the region on Thursday. These were both reported on southeast aspects in the alpine.

There was also a size 3 persistent slab avalanche reported on an east aspect at 2400 m in the neighboring Waterton National Park region on Thursday.

There were several natural and explosives triggered avalanches up to size 2.5 reported in the region on Wednesday.

A natural size 3 persistent slab avalanche was reported on a large south-facing alpine slope in the Crowsnest Pass area last Thursday.  

These recent avalanches are a prime example of the "low probability; high consequence" scenario that persistent slab problems often create. 

Snowpack Summary

15-30 cm of recent snow has been redistributed by strong winds at upper elevations, forming wind slabs in leeward terrain. The storm brought rain to lower elevations, resulting in a crust that is now on the surface up to about 1800 m.

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

  • Avoid freshly wind loaded terrain features.
  • Avoid lee and cross-loaded terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger 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.