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Avalanche Forecast

Archived

Jan 25th, 2019–Jan 26th, 2019

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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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

Glacier.

Reactive wind slabs and a persistent weak layer require careful assessment and thoughtful decision making today.

Weather Forecast

Cloudy with sunny periods and isolated flurries for today. Trace amounts of precipitation, alpine temperature of -8.0, freezing level rises to 1000m and ridge winds west 20-35 km/h. Freezing levels are expected to rise Saturday with an alpine temperature of zero.

Snowpack Summary

Most open terrain in the alpine has been wind affected. In specific locations, strong S winds have redistributed storm snow and created loaded pockets and wind slabs on lee and cross-loaded features at treeline and above. The Jan 17 persistent weak layer down 30cm is surface hoar in sheltered areas and sun crust on solar aspects.

Avalanche Summary

A field team on Macdonald West Shoulder was able to skier control a size 1.0 avalanche on the Jan 17 crust/ surface hoar layer. The team also observed a natural size 2.0 avalanche in the start zone of Macdonald West Shoulder 1. A Na size 2.0 was reported from the S face of Ursus Major Mtn. Limited visibility in the highway corridor yesterday.

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.