Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Jan 16th, 2012–Jan 18th, 2012

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 possible, human triggered probable.

Regions

Purcells.

Confidence

Poor - Track of incoming weather is uncertain on Wednesday

Weather Forecast

There is high uncertainty with the weather for Wednesday and into Thursday. Some forecast models are calling for light to moderate snowfall with associated winds, while others are calling for dry and mostly clear. It all has to do with the track of a frontal system that's primarily heading south of the region. If heavy loading from snow or wind does occur, then expect avalanche danger to increase.

Avalanche Summary

Recent reports indicate loose natural and skier triggered sluffing to size 1.5 in steep terrain. In addition a report of a skier triggered avalanche size 2 on an east aspect in the alpine. Explosives testing in the southern portion of the region on Friday (size 3.5 on a north aspect at 2700m with 200cm fracture) indicates that avalanches are capable of stepping down to deep basal facets with heavy loads. Cornices have also been failing and could be a heavy trigger for wind and persistent slabs on the slope below.

Snowpack Summary

20-45 cm of low density recent storm snow is being redistributed by westerly winds forming weak wind slabs and cornice tabs on lee aspects, but remains fluffy and cohesionless in most sheltered areas. This new snow is bonding poorly to a variety of surfaces (facets, surface hoar in sheltered areas, wind crust, soft slabs and hard slabs).The mid-December surface hoar/facet persistent weakness, now down around 50cm on the eastern side of the range and as deep as 150cm on the western side, is generally producing anywhere from easy (where it's shallow) to hard (where it's deeper) test results. But all tests consistently show a high propensity to propagate fractures. Basal facets remain a concern for human triggering in shallow snowpack alpine areas and for step down fractures in more consolidated snowpack areas.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.