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Avalanche Forecast

Archived

Dec 1st, 2011–Dec 2nd, 2011

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
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

South Rockies.

Confidence

Poor - Due to limited field observations

Weather Forecast

No snow is expected for the next three days. Strong winds are expected from the north early friday morning tapering to moderate and northerly for the rest of the day and into saturday and sunday. Freezing levels are expected to remain at or near valley bottom for all three days.

Avalanche Summary

No new reports received since the weekend; this may say more to the lack of information from the field and little about field conditions. If you have any observations from the field, please drop us an email: [email protected]. Information and observations from you can really help.

Snowpack Summary

Snowfall accumulations have not been sufficient to create an avalanche problem below treeline where the snowpack sits at about 30-60cms. Regardless, slopes at higher elevations have been large enough to run down to terrain located well below treeleine. In the alpine, and at treeline the snowpack depth generally sits anywhere from 80-120cm with deposits of up to 400 cms on wind-loaded features.Although not widespread, reports suggest that strong to extreme winds in some parts of the region have stripped west aspects of snow creating wind slabs on lee and cross-loaded aspects in the alpine and at treeline. Many of these new windslabs could be sitting on the reactive October rain crust located a few centimetres above the ground. This rain crust may have weak, overlying facets and is widespread in the alpine and isolated in its distribution at treeline in some parts of the region and non-existent in others.The 'take home' message is that the region as a whole is data-sparse and extremely variable in terms of snowpack structure. When heading into avalanche terrain, do so gradually and take the time to gather terrain-specific information. Any reports from the field are highly valued. Any observations can be sent to: [email protected]

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.