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Avalanche Forecast

Archived

Jan 25th, 2015–Jan 26th, 2015

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

Regions

Purcells.

We are dealing with a complex avalanche scenario. There is uncertainty in how buried weak layers will adjust to the warm temperatures. Conservative decision making is still recommended.

Weather Forecast

Freezing levels are forecast to remain high through Monday (up to 3000m) before gradually falling over Tuesday and returning to valley bottom by Wednesday. Winds will remain moderate from the south west with a possibility of showers and flurries on Tuesday.

Avalanche Summary

We are moving into a complex avalanche scenario where touchy conditions are likely to persist. A snowpack with several critical avalanche layers has seen incremental loading in the form of new snow and more recently rain. Two recent avalanche cycles have produced increasingly large avalanches primarily on the mid-January surface hoar layer. While the region will see little to no precipitation through the coming forecast period, I anticipate that natural avalanches will remain possible and human triggered avalanche likely as the upper snowpack adjusts to the warm temperatures. Avalanche danger will be higher on slopes exposed to the sun. Warming temperatures will also make cornices more likely to collapse, which in turn could be sufficient to trigger a deep slab avalanche. I would be wary of overhead hazard. At lower elevations I suspect there is the potential for loose wet and wet slab avalanches.

Snowpack Summary

Warm temperatures are encouraging the recent snowfall to rapidly settle into a soft slab. Moderate to strong southwest winds have created wind slabs in lee features. A weak layer of surface hoar buried mid-January lies between 35 and 50 cm below the surface. This layer has been responsible for the majority of the recent avalanche activity and I suspect that we will see it continue to produce avalanches as the snowpack adjusts to the recent snowfall and continued warm temperatures. The mid-December surface hoar/crust layer is typically down 60-120cm below the surface. The reactivity of this deeper weak layer appears to be quite variable but snow pack tests indicate that it still has the potential to produce large avalanches with open slopes at treeline areas being the greatest concern. The mid-Nov weak layer of crusts and facets can still be found near the bottom of the snowpack but has generally become inactive.

Problems

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.