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Avalanche Forecast

Archived

Nov 19th, 2011–Nov 20th, 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.

This bulletin is based on limited data. Local variation in conditions and danger levels are likely to exist. To produce more accurate forecasts, we need information. Please send an email to [email protected]

Confidence

Poor - Due to limited field observations

Weather Forecast

Sunday should continue to be cooler and drier in the morning. The next wave of precipitation should move on to the coast around mid-day Sunday and begin to affect the interior ranges Sunday night and into Monday. This region may be too far East to receive more than light to moderate precipitation. The exception may be the Dogtooth area which may see moderate to heavy precipitation combined with moderate to strong southwest winds.

Avalanche Summary

A cycle of natural avalanche activity was observed in Quartz Creek on Sunday the 13th. 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. We have no new reports of avalanches.

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. Cold temperatures should cause continued facetting on the surface and in the basal layers.

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.