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Avalanche Forecast

Archived

Jan 10th, 2019–Jan 11th, 2019

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

Regions

Purcells.

Warming this weekend will elevate the avalanche danger. Pay particular attention to steep lines off ridges and sun affected slopes.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

THURSDAY NIGHT: Dry, cooling overnight.FRIDAY: Dry with a mix of sun and cloud. Freezing levels rising to around 1400 m. Alpine temperatures around -2C. Light southerly winds.SATURDAY: Dry and sunny. Inverted conditions with an above freezing layer between 1800m and 2500m. Light southerly winds.SUNDAY: Dry and sunny. Inverted conditions with an above freezing layer between 1800m and 2500m. Light southwesterly winds.

Avalanche Summary

On Tuesday, a cornice fall triggered a persistent deep slab avalanche in the north of the region. The avalanche was very large (size 3.5) and released to ground, on a northerly aspect in alpine terrain. A close call (here) also occurred south of the Bugaboos when a group remote-triggered a size 2.5 avalanche from a ridge top. Additionally there were several other reports further south in the region of natural and explosives triggered persistent slab avalanches to size 3.5 on northwest aspects in the alpine.On Monday, a large (size 3) avalanche was triggered by a skier in the north of the region. It is likely that it released on weak faceted grains near the base of the snowpack, as described in the snowpack summary.On Sunday, a small (size 1.5) skier-triggered avalanche was noted in the north of the region. It occurred in steep terrain above a cliff and the avalanche released to the ground, likely within the weak snow described in the snowpack summary.These reports indicate that basal instabilities are still possible to trigger by humans, particularly in the north of the region.

Snowpack Summary

Wind slabs are reported as being widespread in lee and cross-loaded terrain features at treeline and alpine elevations. Wind slabs may be found on all aspects due to variable wind directions.Of concern are the are deeper weaknesses in the snowpack. There is a weak layer around 80 to 120 cm deep, composed of sugary faceted grains, feathery surface hoar, and a sun crust. The base of the snowpack may also still be composed of weak faceted grains. A few large avalanches have recently run on one or other of these layers (see Avalanche Activity Discussion). The possibility of triggering these layers will likely increase with anticipated warm weather. Triggering is also more likely on south-facing slopes and in areas where the snowpack is shallow.

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.

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.