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Avalanche Forecast

Archived

Feb 9th, 2017–Feb 10th, 2017

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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 possible, human triggered probable.

Regions

Little Yoho.

A significant avalanche cycle is starting on Thursday night and will peak on Friday. Avoid avalanche terrain on Friday, and although things may improve slightly for the weekend - extreme winds will keep the avalanche danger high on Saturday.

Weather Forecast

A strong SW flow is driving moisture over the region and bringing extreme winds right through the weekend. Expect a storm total of 30 cm by Friday morning, along with winds in excess of 100 km/hr in alpine areas overnight Thursday. Temperatures are rising also, but look to remain below freezing along the Continental Divide areas through the storm.

Snowpack Summary

10cm of new snow over the past 24-hrs and another 20cm expected by Friday will be blown into deep windslabs by extreme winds from the SW on Thursday night. These new slabs overlie a weak snowpack comprised mostly of facets and depth hoar. Snowpack tests indicate failures, and we expect action on these layers over the next 48-hrs.

Avalanche Summary

Poor visibility today, but during our field trip to Crowfoot Pass in Banff Park, we could hear avalanches occurring in the cliffs overhead.

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.