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Avalanche Forecast

Archived

Jan 12th, 2018–Jan 13th, 2018

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 possible, human triggered probable.
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.

Regions

Little Yoho.

The snowpack has almost reached tipping point with 40cm of soft snow overlying the Dec. 15 weak layer (surface hoar & facets). Warming temperatures and wind this weekend could push it over the edge.

Weather Forecast

A warming trend on Saturday in Little Yoho with temperatures in the -5C range. There will be increased Westerly winds with alpine gusts in the 50-80kmh range and only a couple cm of new snow. The warmer temperatures will continue Sunday.

Snowpack Summary

30-45 cm of low density snow has fallen over the past 5 days with wind effect limited to alpine ridges or the Kicking Horse Pass area (Yoho Blow) where isolated windslabs exist. There is now 30-60 cm overlying the Dec 15 persistent weak layer which is becoming reactive at treeline and below with widespread whumphing observed.

Avalanche Summary

Numerous windslab avalanches up to size 2 were observed to have run during the last storm, mainly near ridge crests or under rock bands where spindrift has accumulated. One size 2 persistent slab was observed near the back of Emerald Lake that failed on the Dec 15 surface hoar.

Confidence

Problems

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.

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.