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Avalanche Forecast

Archived

Jan 18th, 2021–Jan 21st, 2021

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

Regions

Waterton Lakes.

Wind slab remains the primary concern in Waterton but last weeks storm was a reminder of the potential for large triggers to awaken weaknesses deep in the snowpack.

Weather Forecast

Tuesday- Cloudy with isolated flurries. Trace snow at Cameron Lake. Strong SW wind. Freezing level valley bottom.

Wednesday - Cloudy with Sunny periods. No precipitation. Moderate SW wind with strong gusts. Freezing level valley bottom.

Thursday- Mix of sun and cloud. Moderate, maybe even light, SW wind. Freezing level remaining at valley bottom.

Snowpack Summary

There is a surface melt freeze crust up to 1900m on all aspects. Recent storm was accompanied by strong to extreme Westerly wind creating stiff Wind Slabs in lee areas. Multiple layers of wind slab sit over the Dec 9th crust which can be found down 70-100cm near Cameron Lake. Areas east of the divide hold a thin & faceted snowpack.

Avalanche Summary

Public reports in the Wall Lake area mention increased wind slab reactivity in snow pack testing.

Last week we observed a widespread avalanche cycle from Size 1 to 3 that occurred on Tues PM / Wed AM. Some of these involved step down avalanches to deeper weak layers, including a size 3 with impressive propagation in a thin convexity in Rowe Bowl.

Confidence

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.

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.