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Avalanche Forecast

Archived

Nov 16th, 2011–Nov 17th, 2011

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, 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

Purcells.

We have very little information from this region. If you have been in the mountains, send us an email: [email protected] and let us know what you saw.

Confidence

Fair - Due to limited field observations

Weather Forecast

A fast moving storm coming through the Columbias tonight will likely be much less intense in the Purcells. While there's some uncertainty, I'm guessing favoured areas will see 10cm at most overnight Wednesday and only light snow or flurries by Thursday morning. Winds will probably be moderate to strong and variable

Avalanche Summary

A cycle of natural avalanche activity was observed in Quartz Creek on Sunday. Wind slabs (20cm deep) and persistent slabs (60cm deep) were observed. Persistent slabs were propagating widely and running on a weakness towards the base of the snowpack. Observations are limited to the northern Purcells so I don't know if this kind of thing is still occurring here. Avalanche activity may pick up a bit if winds and new snow arrive, more so if the forecast is wrong and more snow falls rather than less.

Snowpack Summary

There is significant variability in the snowpack across the region. Snowpack depth at treeline varies from around 40-130cm. Up to 50cm of snow fell late last week and over the weekend, which was redistributed by strong winds blowing first from the south and then from the north-west. A basal layer of facets was reported in the Dogtooth Range, with a weak interface between the lower facets and recent storm snow. Observations are limited. New snow and wind are in the forecast although not as much as in the Columbias to the west. Some new windslab formation is possible, especially if the actual amount of snow is more than what the forecast calls for.

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.